Prototype device enables photon-photon interactions at room temperature for quantum computing
Ordinarily, light particles—photons—don't interact. If two photons collide in a vacuum, they simply pass through each other.
An efficient way to make photons interact could open new prospects for both classical optics and quantum computing, an experimental technology that promises large speedups on some types of calculations.
In recent years, physicists have enabled photon-photon interactions using atoms of rare elements cooled to very low temperatures.
But in the latest issue of Physical Review Letters, MIT researchers describe a new technique for enabling photon-photon interactions at room temperature, using a silicon crystal with distinctive patterns etched into it. In physics jargon, the crystal introduces "nonlinearities" into the transmission of an optical signal.
"All of these approaches that had atoms or atom-like particles require low temperatures and work over a narrow frequency band," says Dirk Englund, an associate professor of electrical engineering and computer science at MIT and senior author on the new paper. "It's been a holy grail to come up with methods to realize single-photon-level nonlinearities at room temperature under ambient conditions."
Joining Englund on the paper are Hyeongrak Choi, a graduate student in electrical engineering and computer science, and Mikkel Heuck, who was a postdoc in Englund's lab when the work was done and is now at the Technical University of Denmark.
Quantum computers harness a strange physical property called "superposition," in which a quantum particle can be said to inhabit two contradictory states at the same time. The spin, or magnetic orientation, of an electron, for instance, could be both up and down at the same time; the polarization of a photon could be both vertical and horizontal.
If a string of quantum bits—or qubits, the quantum analog of the bits in a classical computer—is in superposition, it can, in some sense, canvass multiple solutions to the same problem simultaneously, which is why quantum computers promise speedups.
Most experimental qubits use ions trapped in oscillating magnetic fields, superconducting circuits, or—like Englund's own research—defects in the crystal structure of diamonds. With all these technologies, however, superpositions are difficult to maintain.
Because photons aren't very susceptible to interactions with the environment, they're great at maintaining superposition; but for the same reason, they're difficult to control. And quantum computing depends on the ability to send control signals to the qubits.
That's where the MIT researchers' new work comes in. If a single photon enters their device, it will pass through unimpeded. But if two photons—in the right quantum states—try to enter the device, they'll be reflected back.
The quantum state of one of the photons can thus be thought of as controlling the quantum state of the other. And quantum information theory has established that simple quantum "gates" of this type are all that is necessary to build a universal quantum computer.
The researchers' device consists of a long, narrow, rectangular silicon crystal with regularly spaced holes etched into it. The holes are widest at the ends of the rectangle, and they narrow toward its center. Connecting the two middle holes is an even narrower channel, and at its center, on opposite sides, are two sharp concentric tips. The pattern of holes temporarily traps light in the device, and the concentric tips concentrate the electric field of the trapped light.
The researchers prototyped the device and showed that it both confined light and concentrated the light's electric field to the degree predicted by their theoretical models. But turning the device into a quantum gate would require another component, a dielectric sandwiched between the tips. (A dielectric is a material that is ordinarily electrically insulating but will become polarized—all its positive and negative charges will align in the same direction—when exposed to an electric field.)
When a light wave passes close to a dielectric, its electric field will slightly displace the electrons of the dielectric's atoms. When the electrons spring back, they wobble, like a child's swing when it's pushed too hard. This is the nonlinearity that the researchers' system exploits.
The size and spacing of the holes in the device are tailored to a specific light frequency—the device's "resonance frequency." But the nonlinear wobbling of the dielectric's electrons should shift that frequency.
Ordinarily, that shift is mild enough to be negligible. But because the sharp tips in the researchers' device concentrate the electric fields of entering photons, they also exaggerate the shift. A single photon could still get through the device. But if two photons attempted to enter it, the shift would be so dramatic that they'd be repulsed.
The device can be configured so that the dramatic shift in resonance frequency occurs only if the photons attempting to enter it have particular quantum properties—specific combinations of polarization or phase, for instance. The quantum state of one photon could thus determine the way in which the other photon is handled, the basic requirement for a quantum gate.
Englund emphasizes that the new research will not yield a working quantum computer in the immediate future. Too often, light entering the prototype is still either scattered or absorbed, and the quantum states of the photons can become slightly distorted. But other applications may be more feasible in the near term. For instance, a version of the device could provide a reliable source of single photons, which would greatly abet a range of research in quantum information science and communications.
"This work is quite remarkable and unique because it shows strong light-matter interaction, localization of light, and relatively long-time storage of photons at such a tiny scale in a semiconductor," says Mohammad Soltani, a nanophotonics researcher in Raytheon BBN Technologies' Quantum Information Processing Group. "It can enable things that were questionable before, like nonlinear single-photon gates for quantum information. It works at room temperature, it's solid-state, and it's compatible with semiconductor manufacturing. This work is among the most promising to date for practical devices, such as quantum information devices."
This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.


Complex oxides are compounds that contain oxygen and at least two other elements. These materials exhibit the unusual electric and magnetic properties needed for next-generation electronic devices. Because silicon is the dominant electronic material, any promising complex oxide should be capable of interfacing with it. However, achieving this interface is challenging. For instance, lead zirconium titanate (PZT) is a well-known complex oxide that is strongly ferroelectric, but it fails to properly “grow” on silicon. One solution is to form thin-film PZT on a compatible substrate and then transfer it to silicon. While conceptually straightforward, the effects of such transfers on thin films are largely unknown. In order to resolve this mystery a research team investigated the properties of a transferred thin film using several techniques, including scanning probe microscopy and charge-voltage relationship measurement performed at Argonne National Laboratory's Material Science Division (MSD), and x-ray nanodiffraction experimentation carried out at the U.S. Department of Energy’s Advanced Photon Source (APS) and Center for Nanoscale Materials (CNM), also at Argonne. The researchers found that the static ferroelectric surface charge and structural properties of the transferred PZT film were more-or-less preserved. However, the ferroelectric’s dynamic electromechanical response changed substantially. Taken together, these findings, published in the journal Advanced Materials, demonstrate the feasibility of transferring thin-film PZT and other complex oxides to silicon, thereby promoting their use for applications including non-volatile computer memory and quantum computing.
PZT was developed in the 1950s as a piezoelectric compound, meaning it produces electricity when deformed, and changes shape in response to an electric field. Due to its excellent piezoelectric properties, PZT is widely used in ultrasound transducers and actuators. This widely-used material is also ferroelectric, meaning that positive and negative charge separation spontaneously arises. Interest in ferroelectrics has increased due to their potential use in computational, switching, and sensor applications. But the advantages offered by ferroelectrics depend upon integration with silicon. Due to their mismatched crystalline structures, PZT will not correctly form on silicon. Fortunately, the lead author of this work previously (while doing postdoctoral research at UC Berkeley) developed an alternative approach known as layer transfer technique (LTT). Using LTT allows scientists to form a thin-film complex oxide on a highly-compatible substrate and then transfer the film to another substrate.
For this study, the researchers from Argonne, the Korea Advanced Institute of Science and Technology (KAIST), and the University of California, Berkeley used pulsed laser deposition to form a crystalline layer of PZT on one substrate and then moved it to another substrate. The researchers were interested in resolving several issues, including whether LTT could transfer a PZT film without destroying it; to provide the first-ever look at the underside of a complex oxide thin-film; and to determine how the transfer affected the film's properties.
Figure 1 illustrates the experimental concept. Thin-film PZT (Fig. 1a) is extracted from the substrate (Fig. 1b) and placed upside-down on a similar substrate (Fig. 1c). This LTT procedure, performed in the CNM cleanroom facility, releases the molecular bonds between the PZT and its original substrate, resulting in a freestanding film resting on the second substrate. Scanning probe microscopy experiments and charge-voltage relationship measurement, performed at MSD, revealed drastically reduced dynamic ferroelectric properties in freestanding film. X-ray nanoprobe data, gathered at the joint CNM/X-ray Science Division 26-ID beamline at the APS, confirmed that the transferred film's crystalline structure remained intact.
Polarized regions are created using scanning probe microscope in ferroelectric films. The nanoscale spaces between two oppositely-polarized areas are called domain walls. Upon applying an electric field, the intervening domain walls can rapidly shift. Taking snapshots of the position of a particular domain wall after applying pulsed electric fields revealed that domain wall movement was 100 to 1000 times slower in the freestanding film versus the originally-deposited form (Fig. 2a). The reduction of domain wall speed was unexpected since theory indicated this speed should actually increase in a strain-free, freestanding film. The researchers attributed the dramatic reduction in wall speed to the induced flexoelectric fields within the film that altered its polarization landscape. The presence of such flexoelectric fields was confirmed by capacitance measurements and numerical simulations. The induced flexoelectric field arose from the pronounced crystallographic tilts caused by thin-film separation, as revealed by the contact mode scanning probe microscopy and x-ray data.
Although wall speed was lowered in the freestanding film, its polarization strength was little changed. The fact that the crystallographic structure and important ferroelectric properties (polarization strength, etc.) were largely preserved in the freestanding PZT film indicates that integrating thin films of complex oxides with silicon is entirely feasible using LTT. However, the researchers note that effects arising from the flexoelectric fields will require additional investigation. ― Philip Koth
See: Saidur R. Bakaul1*, Jaegyu Kim2, Seungbum Hong2, Mathew J. Cherukara1, Tao Zhou1, Liliana Stan1, Claudy R. Serrao3, Sayeef Salahuddin3, Amanda K. Petford-Long1, Dillon D. Fong1, and Martin V. Holt1, “Ferroelectric Domain Wall Motion in Freestanding Single-Crystal Complex Oxide Thin Film,” Adv. Mater. 32, 1907036 (2020). DOI: 10.1002/adma.201907036
Author affiliations: 1Argonne National Laboratory, 2Korea Advanced Institute of Science and Technology (KAIST), 3University of California, Berkeley
Scanning probe microscopy, electronic transport, and sample fabrication carried out at Argonne National Laboratory were supported by the U.S. Department of Energy (DOE) Office of Science-Basic Energy Sciences, Materials Sciences and Engineering Division. Use of the Center for Nanoscale Materials was supported by the U.S. DOE Office of Science-Basic Energy Sciences, under contract No. DE-AC02- 06CH11357. Materials growth carried out at the University of California Berkeley was supported by Office of Naval Research Contract No: N00014-14-1-0654. J.K. and S.H. acknowledge support from Brain Korea 21 Plus and KAIST. This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
The U.S. Department of Energy's (DOE) APS is one of the world’s most productive x-ray light source facilities. Each year, the APS provides high-brightness x-ray beams to a diverse community of more than 5,000 researchers in materials science, chemistry, condensed matter physics, the life and environmental sciences, and applied research. Researchers using the APS produce over 2,000 publications each year detailing impactful discoveries, and solve more vital biological protein structures than users of any other x-ray light source research facility. APS x-rays are ideally suited for explorations of materials and biological structures; elemental distribution; chemical, magnetic, electronic states; and a wide range of technologically important engineering systems from batteries to fuel injector sprays, all of which are the foundations of our nation’s economic, technological, and physical well-being.
The Center for Nanoscale Materials is one of the five DOE Nanoscale Science Research Centers, premier national user facilities for interdisciplinary research at the nanoscale supported by the DOE Office of Science. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia and Los Alamos National Laboratories. For more information about the DOE NSRCs, please visit https://science.osti.gov/User-Facilities/User-Facilities-at-a-Glance.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC, for the U.S. DOE Office of Science.
The U.S. Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit the Office of Science website.


Try a quick experiment: Take two flashlights into a dark room and shine them so that their light beams cross. Notice anything peculiar? The rather anticlimactic answer is, probably not. That’s because the individual photons that make up light do not interact. Instead, they simply pass each other by, like indifferent spirits in the night.
But what if light particles could be made to interact, attracting and repelling each other like atoms in ordinary matter? One tantalizing, albeit sci-fi possibility: light sabers – beams of light that can pull and push on each other, making for dazzling, epic confrontations. Or, in a more likely scenario, two beams of light could meet and merge into one single, luminous stream.
It may seem like such optical behavior would require bending the rules of physics, but in fact, scientists at MIT, Harvard University, and elsewhere have now demonstrated that photons can indeed be made to interact – an accomplishment that could open a path toward using photons in quantum computing, if not in light sabers.
In a paper published today in the journal Science, the team, led by Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, and Professor Mikhail Lukin from Harvard University, reports that it has observed groups of three photons interacting and, in effect, sticking together to form a completely new kind of photonic matter.
In controlled experiments, the researchers found that when they shone a very weak laser beam through a dense cloud of ultracold rubidium atoms, rather than exiting the cloud as single, randomly spaced photons, the photons bound together in pairs or triplets, suggesting some kind of interaction – in this case, attraction – taking place among them.
While photons normally have no mass and travel at 300,000 kilometers per second (the speed of light), the researchers found that the bound photons actually acquired a fraction of an electron’s mass. These newly weighed-down light particles were also relatively sluggish, traveling about 100,000 times slower than normal noninteracting photons.
Vuletic says the results demonstrate that photons can indeed attract, or entangle each other. If they can be made to interact in other ways, photons may be harnessed to perform extremely fast, incredibly complex quantum computations.
“The interaction of individual photons has been a very long dream for decades,” Vuletic says.
Vuletic’s co-authors include Qi-Yung Liang, Sergio Cantu, and Travis Nicholson from MIT, Lukin and Aditya Venkatramani of Harvard, Michael Gullans and Alexey Gorshkov of the University of Maryland, Jeff Thompson from Princeton University, and Cheng Ching of the University of Chicago.
Biggering and biggering
Vuletic and Lukin lead the MIT-Harvard Center for Ultracold Atoms, and together they have been looking for ways, both theoretical and experimental, to encourage interactions between photons. In 2013, the effort paid off, as the team observed pairs of photons interacting and binding together for the first time, creating an entirely new state of matter.
In their new work, the researchers wondered whether interactions could take place between not only two photons, but more.
“For example, you can combine oxygen molecules to form O2 and O3 (ozone), but not O4, and for some molecules you can’t form even a three-particle molecule,” Vuletic says. “So it was an open question: Can you add more photons to a molecule to make bigger and bigger things?”
To find out, the team used the same experimental approach they used to observe two-photon interactions. The process begins with cooling a cloud of rubidium atoms to ultracold temperatures, just a millionth of a degree above absolute zero. Cooling the atoms slows them to a near standstill. Through this cloud of immobilized atoms, the researchers then shine a very weak laser beam – so weak, in fact, that only a handful of photons travel through the cloud at any one time.
The researchers then measure the photons as they come out the other side of the atom cloud. In the new experiment, they found that the photons streamed out as pairs and triplets, rather than exiting the cloud at random intervals, as single photons having nothing to do with each other.
In addition to tracking the number and rate of photons, the team measured the phase of photons, before and after traveling through the atom cloud. A photon’s phase indicates its frequency of oscillation.
“The phase tells you how strongly they’re interacting, and the larger the phase, the stronger they are bound together,” Venkatramani explains. The team observed that as three-photon particles exited the atom cloud simultaneously, their phase was shifted compared to what it was when the photons didn’t interact at all, and was three times larger than the phase shift of two-photon molecules. “This means these photons are not just each of them independently interacting, but they’re all together interacting strongly.”
The researchers then developed a hypothesis to explain what might have caused the photons to interact in the first place. Their model, based on physical principles, puts forth the following scenario: As a single photon moves through the cloud of rubidium atoms, it briefly lands on a nearby atom before skipping to another atom, like a bee flitting between flowers, until it reaches the other end.
If another photon is simultaneously traveling through the cloud, it can also spend some time on a rubidium atom, forming a polariton – a hybrid that is part photon, part atom. Then two polaritons can interact with each other via their atomic component. At the edge of the cloud, the atoms remain where they are, while the photons exit, still bound together. The researchers found that this same phenomenon can occur with three photons, forming an even stronger bond than the interactions between two photons.
“What was interesting was that these triplets formed at all,” Vuletic says. “It was also not known whether they would be equally, less, or more strongly bound compared with photon pairs.”
The entire interaction within the atom cloud occurs over a millionth of a second. And it is this interaction that triggers photons to remain bound together, even after they’ve left the cloud.
“What’s neat about this is, when photons go through the medium, anything that happens in the medium, they ‘remember’ when they get out,” Cantu says.
This means that photons that have interacted with each other, in this case through an attraction between them, can be thought of as strongly correlated, or entangled – a key property for any quantum computing bit.
“Photons can travel very fast over long distances, and people have been using light to transmit information, such as in optical fibers,” Vuletic says. “If photons can influence one another, then if you can entangle these photons, and we’ve done that, you can use them to distribute quantum information in an interesting and useful way.”
Going forward, the team will look for ways to coerce other interactions such as repulsion, where photons may scatter off each other like billiard balls.
“It’s completely novel in the sense that we don’t even know sometimes qualitatively what to expect,” Vuletic says. “With repulsion of photons, can they be such that they form a regular pattern, like a crystal of light? Or will something else happen? It’s very uncharted territory.”
Massachusetts Institute of Technology
Observation of three-photon bound states in a quantum nonlinear medium, Science (2018). science.sciencemag.org/cgi/doi … 1126/science.aao7293
Credit: Science (2018). 10.1126/science.aao7293


Microwave photonics circuit elements will need to be similar to their RF analogs to provide the desired functionality.
One of these analogous circuit elements is a terahertz microwave cavity resonator, which can be integrated onto an IC with standard CMOS processes.
This is one of many circuit elements that can be placed on an IC and used to enable unique applications.
These fibers will soon be integrated into semiconductor wafers as microwave lines to communicate with unique circuit elements like terahertz microcavity resonators.
Microwave components have a lot more going on than what ends up in your microwave oven. Terahertz wave sources, detectors, and components have yet to be miniaturized, and the terahertz portion of the microwave spectrum is still largely unexplored. So far, the best we can do is get into the high GHz (low THz) region for oscillation, detection, and wave manipulation. This region is critical for many applications, including quantum computing, imaging, sensing, and ultra-fast communication.
One fundamental set of components is terahertz microcavity resonators. These components are part of a larger photonics platform and they play analogous roles to RF resonators on a PCB. The simple geometry of these resonators also allows them to be placed on a chip alongside other photonic structures. If you’re a budding photonics engineer, keep reading to learn more about these resonator structures and how they might play a role in current and upcoming photonics systems.
What Are Terahertz Microcavity Resonators?
Much like any other resonator, terahertz microcavity resonators have a fundamental frequency that lies in the terahertz region. In terms of wavelength, a 1 THz wave in air has a wavelength of only 300 microns, which is quite large compared to today’s transistors. These structures provide the same function as well; they allow a wave matching the fundamental frequency or one of its harmonics to excite a high-Q resonance, whereby a standing wave can form in the cavity.
Much like a wave on a string or in a waveguide, this standing wave at one of the eigenfrequencies will have very high intensity due to constructive interference inside the cavity. The very strong, very coherent electromagnetic wave in this structure can then be used for some other application. The challenges in working with these structures are wave generation and detection, both of which need to be solved for terahertz microcavity resonators to be useful at the chip level.
Geometry and Eigenfrequencies
The image below shows a simple rectangular terahertz microcavity resonator and its discrete eigenfrequency spectrum. The eigenfrequencies can be tuned to desired values by adjusting the geometry, just like any other resonator. The equation below applies to a closed rectangular cavity and provides a good first approximation for a slightly lossy cavity (i.e., with high dielectric constant contrast at the edge).
Rectangular terahertz microcavity resonator geometry and eigenfrequencies.
Although a rectangular geometry is shown above, more complex structures may be used for different applications. In a different structure (e.g., circular, hemispherical, or cylindrical) with an open edge, the eigenfrequencies may not obey such a simple equation. Instead, they may be determined from a dispersion relation that is a transcendental equation, which requires a numerical technique to extract specific frequencies. This is a well-known procedure for solving Sturm-Liouville problems in waveguides and resonators.
If you have a much more complex structure that can’t be approximated as a simple shape, the various eigenfrequencies and the spatial distribution of the electromagnetic field can be determined using a 3D field solver (FDFD technique). A field solver you would normally use for IC packages can also be used for modeling terahertz microcavity resonators.
Applications for terahertz microcavity resonators are still being researched, as are the device architectures required for different applications. Some proposed applications of terahertz microcavity resonators include:
Sensing and imaging: High-Q terahertz microcavity resonators can be used for highly coherent imaging and sensing, with applications in molecular detection and biological imaging.
Silicon photonics: While this application area is normally discussed in terms of SMF or MMF wavelengths, devices in this area can also operate at THz frequencies and will need terahertz microcavity resonators to act as filters and amplifiers.
Communication: Currently, the world record for the highest data rate transmission belongs to an experimental wireless system operating at THz frequencies. Miniaturizing these systems at the chip level will require microcavity structures, including terahertz microcavity resonators.
The important advancement provided by these structures is that they can occur on an integrated circuit. Today, these applications still involve large optical systems where an infrared mode comb in a femtosecond soliton laser is used to generate a terahertz wave through interference. Similarly, large systems are also used for the detection and manipulation of terahertz waves. Terahertz microcavity resonators are one class of components that can provide high-Q or low-Q reception of THz frequencies, which can then be passed to a detector element or other photonic circuit.
The range of useful materials for building terahertz microcavity resonators, or for building coupling structures, is also an open research question. Some material platforms used for terahertz microcavity resonators include:
Silicon: This material is the most promising for the fabrication of terahertz devices and their integration alongside other electronic circuits.
GaAs, other III-V’s, and II-VI’s: This promising set of photonic materials has already shown interesting results at ~3 THz frequencies, particularly for the generation of laser light. This material platform is promising for photonics in general.
Photonic crystals: Periodic nanostructures that are fabricated through chemical deposition methods provide a tunable platform for fabricating a range of terahertz devices, including terahertz microcavity resonators.
Dielectrics: This broad range of materials includes oxides, salts, polymers, and other materials that can support transmission or absorption in various THz frequency ranges. For integration, the best set of materials should bond to the industry’s current range of semiconductors.
Microcavity resonator materials should be chosen to integrate into existing semiconductor materials platforms and manufacturing processes.
As your technology and designs push into more advanced spaces with the years to come, more advanced software that can navigate the nuances and challenges of THz components will be necessary. Be sure to prepare adequately as you stay ahead of the frequency curve.
About the AuthorFollow on Linkedin Visit Website More Content by Cadence PCB Solutions


Coursing through the fiber-optic veins of the Internet are photons of light that carry the fundamental bits of information. Depending on their intensity, these photons represent bits as 1s and 0s. This on-and-off representation of information is part of what physicists call “classical” phenomena.
But photons of light have “quantum” properties as well, which, when exploited, provide more than simply a 1 or 0; these properties allow photons to represent 1s and 0s simultaneously. When information is approached from a quantum perspective, say scientists, encryption can be perfectly secure and enormous amounts of information can be processed at once.
This field of quantum information –- the transmission and processing of data governed by quantum mechanics –- is rapidly moving beyond the lab and into the real world. Increasingly, researchers are conducting experiments within the same commercial fiber that transmits information in the classical way. For the most part, though, the two types of information have not intermingled: quantum information has been sent only over dedicated fiber.
Now researchers at Northwestern University have shown that quantum information, in the form of “entangled photons,” can travel over the same fiber as classical signals. Additionally, the researchers have sent the combination signal through 100 kilometers of fiber – a record distance for entangled photons even without the classical signal.
This marriage of quantum and classical optics shows that traditional optical tools can be used to send quantum encryption keys, based on entangled photons (some other schemes rely on single photons). In the future, this new technique might also enable long-distance networking between quantum computers, says Carl Williams, coordinator of the Quantum Information Program at the National Institute of Standards and Technology in Gaithersburg, MD.
At the heart of the Northwestern experiment are the entangled photons: pairs of photons with interconnected properties. That is, looking at one photon in an entangled pair will reveal what the result of looking at the other photon would be – no matter how far apart the photons are. Entangled photons can be used in encryption by encoding information about a key in the photons. Then if an eavesdropper intercepts one photon of the entangled pair, the entire transmission is altered, alerting the code makers.
Furthermore, entangled photons used for quantum computing could be split up and shared across a network of many quantum computers. Such photon pairs are “important whether the application is cryptography or anything else,” says Prem Kumar, professor of electrical and computer engineering and physics at Northwestern and lead scientist on the project.
The first step in the experiment, then, was for the researchers to create entangled photons. Traditionally, shining laser light into a type of crystal has produced entangled photons. But it’s been difficult to use entangled photons made from crystals, because in transferring them into a fiber, you “lose the quality of the entanglement,” says Williams.
Instead, Kumar’s team created their photon pairs by exploiting a similar, recently developed process that can occur within long lengths of standard fiber. The photons start in fiber and remain in it for the duration of the experiment, retaining their entanglement properties.
The researchers pulsed polarized laser light through 300 meters of coiled fiber. It is this property of polarization (the orientation of the photons) that allows it to become entangled when the pairs of photons are created: if the polarization of one photon is measured, the polarization of the other photon is instantly known. Within the fiber, about one pair of polarization-entangled photons is created every microsecond, Kumar says, and the rate can be increased 100-fold by pulsing the light faster, he adds.
Next, the entangled photons are split apart and each is directed into 50 kilometers of fiber (for a total of 100 kilometers), where they join a classical signal. At the opposite ends of the fibers, the photons are separated from the communication signals, and shoot towards two different photon detectors, built to see one photon at a time. Kumar says he knows he’s successfully sent entangled photons when both detectors see certain types of polarized photons at the same time.
There are still challenges to using traditional fiber-optic cable and sending entangled photons 100 kilometers. Even the best quality commercial fiber has very small geometric inconsistencies, Kumar says, which can alter the polarization of the photon pairs slightly, decreasing the quality of entanglement – and rendering the quantum information useless.
These slight changes in polarization can usually be adjusted for by sending the photons through special polarization devices right before they hit the detector, but it is difficult to know exactly how to adjust these devices to best compensate for the change in polarization. Interestingly, Kumar adds, the classical signal traveling with the quantum signal, as in the experiment, can help. It can track imperfections in the fiber encountered by the entangled photon, and relay this information so the polarization control device can be set to compensate appropriately.
Right now, Kumar’s team is working on testing the distance limits of entangled photon transport and determining how many more classical signals they can add to the line and still retrieve the quantum information stored in the entangled photons. Because in real-world fiber optics, multiple signals pass through at once, it would be useful to know how many classical signals can share the fiber with a quantum signal.
According to other scientists working in the field of quantum information, the fact that Kumar’s team has combined fiber-generated entangled photons with classical information, and sent the total signal over a record distance in a traditional fiber line is an exciting advance. “Pieces have been shown, but this puts it all together,” says Williams, who calls it “a remarkable demonstration.”
Jeffrey Shapiro, professor of electrical engineering at MIT, says it is “great work…Prem [Kumar] works both on classical and quantum communication, and is one of the people who’s well suited to address both sides.”
Ultimately, as quantum information matures, it will become more integrated into traditional fiber technology, says Kumar. “My goal is to make quantum optics applicable,” he notes. “Fiber-based quantum optics can piggyback on billions of dollars in optical communications technology. We want to ride that wave.”


Atoms are tricky to control. They can zip around, or even tunnel out of their containment. In order for new precision measurement tools and quantum devices to work—and work well—scientists need to be able to control and manipulate atoms as precisely as possible.
That’s especially true for optical atomic clocks. In these clocks, a cold, excited atom’s electrons swing back and forth in what’s called a dipole, vibrating like a plucked string. Scientists rapidly count those swings with a laser, dividing a second into quadrillionths of a second.
However, even the best optical atomic clocks face decoherence—the atom falls back to its ground state, the laser loses the signal, and the clock winds down. This means optical atomic clocks can only take measurements for a few seconds before the atoms need to be “reset.”
Scientists are continually exploring ways to increase those coherence times. Using optical tweezers, Aaron Young, along with other members of the Kaufman and Ye groups at JILA, have reached record-setting coherence times of more than half a minute. Their findings were recently published in Nature.
“The trick is to use separate sets of tweezers to prepare and measure the atoms, and to hang on to the atoms while they ring down. This makes it possible to optimize the second set of tweezers to preserve coherence for as long as possible, without having to worry about competing requirements associated with other phases of the experiment,” Young said.
Optical atomic clock technology
Optical atomic clocks are incredibly varied, but there are two popular means for controlling the atoms: ion traps, and optical lattices for trapping neutral atoms. Each approach has its strengths and weaknesses.
Trapped ion clocks measure the oscillations of a single charged atom, or ion. That atom is pristine, well-characterized, and well-controlled, however, due to the fundamental noise associated with quantum measurements, scientists need to run the trapped ion clock many times to obtain a precise measurement.
Lattice clocks, on the other hand, use standing waves of reflected lasers to form an egg carton-shaped lattice that can hold many atoms. This way, they can interrogate many thousands of atoms in parallel to obtain precise measurements in a short amount of time. But it’s difficult to control any of those thousands of atoms individually, and interactions between these atoms must be well-characterized — a rich and complicated endeavor in its own right.
Controlling and preventing these interactions is where optical tweezers come in. Optical tweezers are highly-focused laser beams capable of grabbing and moving individual atoms—something the Kaufman Group has a lot of experience doing.
“With the tweezers, our traps are more or less independent,” Young said. “It gives you a lot of control over what kind of traps you can make.”
The group uses this extra control to preserve quantum coherence, and minimize many of the effects that can limit clocks.
A hybrid clock of cigar pancakes
Young and the team used lasers to create a vertical lattice of traps, like stacked pancakes. The optical tweezers pierce these pancakes, looking like little cigar-shaped tubes. This creates a two-dimensional array composed of hundreds of spherical traps that each contain a single atom.
This pancake-cigar architecture allows for very quick cooling and trapping of the atoms, at which point they are easily transferred to a second set of tweezers designed specifically for clock physics.
Because the atoms are well-chilled, the second set of tweezers can make very shallow traps for the clock. Shallow traps minimize the number of photons that could interfere with the atoms, and they reduce the power required for the laser, making it possible to make more traps, and trap more atoms. They can also space these traps far enough apart so the atoms cannot move around or crash into their neighbors.
All of this results in record coherence times—48 seconds.
To put that in perspective, if every oscillation took about a full second—like the pendulum on a grandfather clock—you would only have to wind this clock once every few billion years.
“This long lifetime is related to what people call a ‘quality factor’ – it’s the number of times an oscillator swings before it rings down. The quality factor of our experiment is the highest we know of in pretty much any physical system, including, depending on how you compare them, various astronomical systems like spinning neutron stars or planetary orbits,” Young said.
More than a clock
“What we’ve effectively done is put 150 very coherent qubits in the same place, which serves as a really good starting point for engineering interactions,” Young said.
A clock with controllable interactions could be used to engineer quantum states that allow for even more precise measurements of time.
But the Kaufman and Ye Groups see potential to use this technique for another quantum device: quantum computers. With exquisite control of each high-coherence atom, the atoms can act as a qubit for the computer to perform calculations.
Young and Kaufman also see this as a “zeroth order step” in physics research. Physicists are continually seeking better control over atoms to manipulate interactions between them, and study the results—and this hybrid tweezer clock is a promising means of achieving that control for long periods of time. By studying and controlling those interactions, physicists can better understand how the quantum world works, and those discoveries could lead to new advances in quantum-based technologies.
Their study was published in Nature on December 17th, 2020 and was supported by a National Science Foundation Physics Frontier Center grant and a grant from the National Research Council.


Our connected devices are hiding a big secret. They use energy—a lot of it. Every time you use your phone, your computer, or your smart TV to access the internet, you’re sending data requests to warehouse-sized buildings around the world, full of hundreds of thousands of servers. These data centers are among the most energy-intensive systems on the planet, representing approximately 10% of global electricity generation (though more conservative estimates put it at 3%).
Yet we’re still blindly making classic computers—and they’re getting bigger and even more energy dense. China is home to the most energy-intensive supercomputer in the world, the Tianhe-2 in Guangzhou. This machine uses about 18 megawatts of power, and is expected to be succeeded by the exascale Tianhe-3, which will only further increase this extraordinary level of energy consumption. For reference, the average hydroelectric dam in the US produces approximately 36 megawatts of power.
This is just one reason why quantum computing is key to the future. In addition to holding the potential to solve some of the world’s most computationally challenging problems, quantum computers use significantly less energy, which could lead to lower costs and decreased fossil-fuel dependency as adoption grows. (Disclosure: I’m also the CEO of a quantum-computing company.)
Unlike classical computers, which use binary bits to encode information as 1s or 0s, quantum computers work using qubits. Thanks to the “weirdness” of quantum mechanical properties, qubits can represent both 1s and 0s at the same time, allowing quantum computers to find optimal solutions that classical systems cannot, all while using less energy.
Here’s why: For a quantum processor to exhibit quantum mechanical effects, you have to isolate it from its surroundings. This is done by shielding it from outside noise and operating it at extremely low temperatures. Most quantum processors use cryogenic refrigerators to operate, and can reach about 15 millikelvin–that’s colder than interstellar space. At this low temperature, the processor is superconducting, which means that it can conduct electricity with virtually no resistance. As a result, this processor uses almost no power and generates almost no heat, so the power draw of a quantum computer—or the amount of energy it consumes—is just a fraction of a classical computer’s.
And then there’s the price. Most modern classical supercomputers use between 1 to 10 megawatts of power on average, which is enough electricity to meet the instantaneous demand of almost 10,000 homes. As a year’s worth of electricity at 1 megawatt costs about $1 million in the US, this leads to multimillion-dollar price tags for operating these classical supercomputers. In contrast, each comparable quantum computer using 25 kilowatts of power costs about $25,000 per unit per year to run.
Businesses are constantly looking for a competitive advantage, especially in an era of shrinking margins and fierce competition. In the case of computing, they’re looking for better, faster, or more efficient ways to solve problems than a classical computer. In the future, most quantum applications will utilize hybrid computing, which is a combination of classical and quantum computing that will provide a workable alternative to this unsustainable status quo—one that unlocks new commercial applications while dramatically curbing energy usage and costs.
With hybrid, the hard parts of commercial computing that aren’t suitable for existing classical systems can be sent to a quantum processing unit and returned to a classical computer. High-energy portions of hybrid applications will be run on quantum computers—often through the cloud—while the low-energy pieces are reserved for classical. Hybrid computing means utilizing the best of both the quantum and classical worlds, and lowering the barriers for companies of all sizes to get started using quantum computers.
Thanks in part to hybrid computing, early quantum applications are already being used in industries including automotive, manufacturing, and finance. Volkswagen is using quantum computers to build early applications that will be able to optimize public transportation routing in cities around the world. DENSO, a leading auto-parts manufacturer based in Japan, has reported that it can reduce gridlock and improve efficiency of autonomous robots on its factory floors with the help of an application built with a quantum computer.
Quantum computing is showing signs of early benefits today, but there’s more to do before we see fully practical deployment of quantum computing in production. We need continued buy-in and investment from both governments and businesses to achieve widespread adoption. We also need to train and develop the next generation of expertise and talent in the quantum workforce. Finally, we need to continue breaking down barriers to using quantum computers with affordable, flexible cloud access and developer-friendly software and tools.
Quantum computers hold the promise to solve today’s toughest business problems and impact the bottom line for companies in virtually every industry. They’re also a key tool we can use to combat the looming threat of ever-growing energy use of classical computing. Businesses are already starting to feel the pressure to get their heads in the quantum-computing game, but the impetus goes beyond innovation and technological competition for a single company. It extends to a collective goal: ensuring our world’s computing power doesn’t outstrip our planet’s ability to support it.
Correction: The previous headline for this piece “We’ll run out of energy in 20 years if we don’t switch to quantum computing” overstated the threat to global energy production. The headline has been updated to better reflect the article text. In addition, the article has been updated to more accurately explain the costs of electricity generation and use.


If you are looking for some great science websites for interactive learning, then these eleven plus sites should, at the very least, scratch and itch. Most of these are aimed at younger learners but some will be as, if not more, entertaining for adults.
1. Khan Academy is great for people of all ages
Khan Academy is one of the best resources for STEM learning on the web. And, guess what? It is free. This interactive website is filled to the brim with fantastic content led by professionals and teachers who are experts on the content, with the occasional STEM celebrity appearances.
There is not that much gamification on this website. Most of the learning is done through fun interactive quizzes. The site is perfect if you need to build on the current topics you are learning from at school or are an adult. Khan Academy has courses for every level, from elementary school to college.
2. Curiosity Machine will teach you about AI
Curiosity Machine helps children build, share, and receive feedback from experts. Its main focus is on teaching children, and their parents, about the power of Artificial Intelligence.
Its main focus to bring family members together to learn and build their own AI.
It has a specific "Family Challenge" which is a "free, hands-on AI education program that brings families, schools, communities, and technology know-it-alls together to give everyone the chance to learn, play and create with AI."
Families will be guided through the basics of AI and are then encouraged to look around their local communities for potential problems to solve using their new skills. Proposals can then be submitted to win the competition.
3. Teachers TryScience is full of online experiments
Teachers TryScience is a website specifically designed to spark any young mind's interest in science, technology, engineering, and math. At its very core, it aims to bring design-based learning to children at home or at school.
According to the website, it helps children "to solve a problem in environmental science, students might need to employ physics, chemistry, and earth science concepts and skills."
To this end, it has a large collection of interactive experiments, field trips, and other adventures. It also includes lesson plans, strategies, and tutorials for teachers to better help them deliver awe-inspiring science lessons for their ever-curious students.
4. The Exploratorium is the go-to site for interactive learning
The Exploratorium is the website arm of the San Francisco Exploratorium. This site offers hands-on experiences that will help teach children about basic, and more complex, scientific principles.
It covers subjects from many disciplines of science from biology and earth science to astronomy. The site also has a parent and teacher section that will provide free resources to help you plan and incorporate its interactive material to boost your child's learning.
5. Science Kids will engage your kid's mind
Science Kids is another interactive learning website that focuses on teaching children the wonders of science. The site has a great variety of interactive science games covering subjects from living things to physical processes and everything in between.
The great thing about this site's content is that it not only educates young minds but helps them put that knowledge to practical use to cement it in their memory. One particularly useful game will have your child design and build a virtual electrical circuit.
Each subject comes in modules that are then subdivided into subcategories. Living things, by way of example, is divided into food chains, microbes, and the human body, etc.
6. BrainPOP will do just that
BrainPOP is the place for science learning and it's very well designed to boot. It is a very active site for young students with a myriad of animations, movies, and short interactive quizzes.
It covers topics like cellular life and genetics, ecology and behavior, forces of nature, our fragile environment, scientific inquiry, and paleontology and anthropology. So young aspiring scientist is bound to find something that will spark their interest.
It also has some interactive coding lessons which are always fantastic ways to learn something they might not normally be exposed to. The site will have them hacking government websites in no time - only joking of course.
7. HHMI Biointeractive - it's in the name
HHMI's website is full of great 3-D interactive, virtual labs, and printable activities for you to use. Its material is both engaging and interesting for science-buffs of all ages.
These guys are famed for their award-winning virtual labs and high-quality informative videos so you know you are in good hands. Their site includes "Click & Learn" activities that include embedded video clips and animations, videos all of which have stop points and assessments to help check you've been paying attention.
8. Annenberg Learner Interactives is a great resource for Earth Science students
Annenberg Learner Interactives' Earth Science-related topics are full of great and easy-to-understand graphics and other interactive content. It has a good collection of interactive lessons cover the big things like the Earth's structure to plate tectonics.
The site also covers many other subjects within Earth Sciences, such as the Rock Cycle and Volcanoes, which really makes this subject come alive to any young student. It also has other resources for other scientific subjects with interactive games and other lessons.
9. National Geographic Kids is fun and educational
Being created by National Geographic you know you can trust this site to be top quality. And it doesn't disappoint.
This site includes a large collection of videos, interactive activities, and fun games that will keep children of all ages engaged for hours on end.
National Geographic Kids' site is broken down into helpful subcategories for ease of navigating your child's learning. Each section contains extensive and informative write-ups on different animals from lions to whales supported with world-class National Geographic footage.
Each section also includes memory games, quizzes, and other different activities to reinforce their learning by applying their new-found knowledge.
10. PhET Interactive Simulations is all about Physics simulations
PhET Interactive Simulations is a real gem of an interactive and fun science-related website. Built and run by the University of Boulder, Colorado it has a vast collection of simulators covering most topics with physics from circuits to waves to quantum mechanics.
Be warned, however, you might find yourself aimlessly playing around with variables without noticing hours of your precious time have passed by. Do not, we repeat do not, try the spring simulation it is too much fun.
It also has some materials covering Earth Science, chemistry, and life sciences but these are far less extensive.
11. Wonderville is great for all ages
Wonderville is another great science-related website that is packed with interactive activities for children.
According to the website Wonderville "makes learning science fun for kids. We help teachers teach and students learn. Used in 170 countries, our awarding-winning STEM content helps create lifelong learners."
Other than fun and entertaining games it also has a very good blog for the more curious children who want to go deeper into a subject.
Adults love using Brilliant.org. The interactive games on this website do not try to teach you through memorization. The Brilliant team is dedicated to teaching you how to think critically about STEM topics. From Geometry to Quantum Computing, this website is an excellent way to spend your free time, if you are a dedicated life-long learner. Scientific Thinking is one of our favorite courses on Brilliant.Org.
13. The Raspberry Pi Foundation
Raspberry Pi is a powerful but tiny affordable computer that can be used to do everything from creating your own DIY projects at home to learning programming. The mini-computer is great for both kids and adults interested in getting into the science of computing and programming.


Scientists at Cambridge University are working on combining two fields of solid state physics research, spintronics and superconductors, in order to develop what they hope could become the foundation for the next generation of datacenter technology — perhaps within the next decade.
Data centers are the engines of the digital economy. But they are also very energy intensive in their own right — with the researchers citing estimates that some three per cent of the power generated in Europe is already being used by data centers.
One impetus for the research is therefore to apply ‘superspin’ technology to substantially reduce the power consumption of high performance computing and data storage. Superconductors allow for the propagation of electrical charge without electronic resistance, and therefore hold out the tantalizing promise — in computing kit terms — of carrying electronic charge with zero energy loss.
Albeit, at this stage in the research, there is still a question mark over whether the cooling requirements of utilizing superconductors will result in less energy consumption overall or not. Hence the need for further research.
“Superconductivity necessarily requires low temperature,” explains Dr Jason Robinson, one of the project leads. “No one has discovered room temperature superconductivity.
“The crunch question is: is the energy required to cool going to be smaller than current energy loss due to the energy efficiency of spintronics. If it costs more to cool than it currently does in terms of what we lose, currently, then it’s not worth it. That’s what we’re exploring.”
“Our basic calculations suggest that superconducting spintronics will be massively more energy efficient than current spintronics,” he adds.
Another driver for the research is to use superspin as a possible alternative to semiconductor technology — as a new route to sustain Moore’s Law of shrinking electronics, just as the ability of engineers to pack more transistors onto integrated circuits is starting to look like it’s coming to the end of the road. Spintronics proposes utilizing the spin alignment of electrons as a medium to store (the 0 or 1 of) digital data.
“Information technology now is based on such small objects you just can’t use conventional superconductors,” notes Robinson. “By combining superconductivity with spintronics it’s not only that you can create circuits without [energy] dissipation, but it’s that you create new physics. So that means there’s a lot of new opportunities created through this combination.
“There’s a lot of undiscovered physics to be explored.”
The Cambridge-led project has received a £2.7 million grant from the UK’s Engineering and Physical Sciences Research Council, with a focus on developing a superconducting spintronics prototype device over the next five years to prove out their theoretical modeling that the combined tech is indeed more energy efficient than just using spintronics.
“It’s important to understand that this is the first ever superconductivity and spintronics funded program,” adds Robinson. “The way the grant has been set up in the first three years there’s a series of parallel projects. Some are more applications biased than others but the application stuff has to develop alongside the science… Everything we do is moving us towards the prototype.”
“It’s a fundamental program with the aim of triggering applications in spintronics. There’s a lot of science we don’t currently understand and we need to understand in order to be able to make the best possible prototype. We have enough science to know that we can make a prototype. The question is can we make the best prototype,” he adds. “[And] what do we need to do in order to be able to make a device that’s switchable — that you can not only store information on, but you can process information with as well.”
The project draws on prior research conducted at Cambridge, and elsewhere, to combine spintronics and superconductors — a feat previously thought to be impossible, thanks to superconductivity canceling out electronic spin.
However the same research group at Cambridge found a workaround for that, involving magnets. Initially utilizing a layer of a rare earth magnetic material — although the group has since proved that various magnetic materials can be used, according to Robinson.
“A few years ago our group discovered that actually if you combine supercomputers with magnets you can create a new kind of Cooper Pair [paired electrons], which instead of having two electrons with anti-parallel spins you can create pairs which have parallel line spins. So now you have both the benefits of superconductivity and the ability to carry spin in the superconducting state.”
Another area he is excited about from the combination of superconductivity and spintronics is the potential for using the technique to further quantum computing.
“It introduces lots of new ideas that were not possible previously. So that’s exciting, and indeed a large part of our grant is to develop the science of those other areas as well,” he adds.


Where would we be without computers? Whether giving us the chance to work remotely, work on files with colleagues in real time, or for recreational activities like streaming – there can be no doubt that computing devices have changed the way we go about our day-to-day lives.
However, while more ‘traditional’ computers are great for completing run-of-the-mill tasks, there are many more complex problems in the world that these machines will struggle to solve. For problems above a certain size and complexity, traditional machines simply don’t have enough computational power to tackle them. To put this in perspective, Fugaku, the world’s fastest supercomputer is over 1,000 times faster than a regular computer, and, in 2019 Google claimed its Sycamore quantum processor was more than a billion times faster at solving problems than a supercomputer.
Given their processing superiority, if we want to have a chance at solving some of the world’s most complex issues, we must look to quantum computers.
Understanding Quantum Computing
In case you are unfamiliar with the concept, quantum computing leverages the substantial mechanics principles of superposition and entanglement in order to create states that scale exponentially with the number of quantum bits – or ‘qubits’. Rather than just being on or off, qubits can also be in what’s called ‘superposition’ – where they’re both on and off at the same time, or somewhere on a spectrum between the two.
Put more simply, for scientists to properly simulate scientific situations, the calculations they make on a computer must be able to handle uncertainty in the way that traditional, and even supercomputers can’t. This is the key characteristic of quantum computing.
Today, real quantum processors are used by researchers from all over the world to test out algorithms for applications in a variety of fields. Indeed, these computers may soon be able to spur the development of new breakthroughs in science, medication for currently incurable diseases, discovering materials to make more efficient devices and structures like more powerful solar panels as well as creating algorithms to quickly direct resources to where they are needed, such as ambulances.
Quantum Computing and Cybersecurity
However, not only do these machines have to be protected from hackers, they themselves could also pose a threat to digital life as we know it.
Right now, for example, cyberattacks can be carried out with relative ease, due to the fact many organisations do not have protections in place for their confidential information. As such, placing a much greater emphasis on improving the security of communications and data storage is crucial for guaranteeing the protection of sensitive information for states, private entities and individuals, than say 20 years ago. However, if quantum computers can launch attacks that break asymmetric cryptography, they then render the entire PKI-based encryption method we currently use to protect our sensitive information, obsolete. Which begs the question: Then what?
To take advantage of the time quantum computers will be able to break such systems, some countries are already beginning to collect encrypted foreign communications, with the expectation that they will be able to extract valuable secrets from that data in the future. Indeed, countries need to be aware that when quantum cryptanalysis does become available, it will significantly affect international relations by making any broadcast communications in the state open to decryption. For countries that extensively rely on encryption to secure military operations, diplomatic correspondence or other sensitive data, this could be a watershed event.
As quantum computers continue to improve, businesses and the general public will become increasingly aware of the threat cryptographic systems pose to all digital security globally. The ability to update cryptographic algorithms, keys and certificates quickly in response to advances in cracking techniques and processing speed will therefore be key.
To prepare for these inevitable cryptographic updates, more enterprises than ever will need to explore automation as a critical component for ensuring future-proofed security. Quantum resistant communication technology will soon be an inevitable part of cybersecurity mitigation.
Business and technology strategists must monitor progress on the evolution and potential implications of quantum computing starting now. Confidential data, over-the-air software updates, identity management systems, connected devices, and anything else with long-term security obligations must be made quantum safe before large quantum computers are developed and are reliable, meaning their error rates are low.
We have announced collaborations with ISARA Corporation and ID Quantique to make quantum-safe crypto more widely available for data protection in the cloud, applications and networks. Innovations like these can help combat the future security threats of quantum computing. With governments and organisations, such as NIST, racing to become cryptographically quantum resilient, readying enterprises for this change has never been more important.
*** This is a Security Bloggers Network syndicated blog from Enterprise Security – Thales blog authored by Aline Gouget. Read the original post at: https://dis-blog.thalesgroup.com/security/2020/08/05/quantum-computing-and-the-evolving-cybersecurity-threat/


Quantum computing is inevitable; cryptography prepares for the future
Quantum computing began in the early 1980s. It operates on principles of quantum physics rather than the limitations of circuits and electricity, which is why it is capable of processing highly complex mathematical problems so efficiently. Quantum computing could one day achieve things that classical computing simply cannot.
The evolution of quantum computers has been slow. Still, work is accelerating, thanks to the efforts of academic institutions such as Oxford, MIT, and the University of Waterloo, as well as companies like IBM, Microsoft, Google, and Honeywell. IBM has held a leadership role in this innovation push and has named optimization the most likely application for consumers and organizations alike. Honeywell expects to release what it calls the “world’s most powerful quantum computer” for applications like fraud detection, optimization for trading strategies, security, machine learning, and chemistry and materials science.
In 2019, the Google Quantum Artificial Intelligence (AI) team announced that their 53-qubit (analogous to bits in classical computing) machine had achieved “quantum supremacy.” This was the first time a quantum computer was able to solve a problem faster than any classical computer in existence. This was considered a significant milestone.
Quantum computing will change the face of Internet security forever — particularly in the realm of cryptography, which is the way communications and information are secured across channels like the Internet. Cryptography is critical to almost every aspect of modern life, from banking to cellular communications to connected refrigerators and systems that keep subways running on time. This ultra-powerful, highly sophisticated new generation of computing has the potential to unravel decades of work that have been put into developing the cryptographic algorithms and standards we use today.
Quantum computers will crack modern cryptographic algorithms
Quantum computers can take a very large integer and find out its prime factor extremely rapidly by using Shor’s algorithm. Why is this so important in the context of cryptographic security?
Most cryptography today is based on algorithms that incorporate difficult problems from number theory, like factoring. The forerunner of nearly all modern cryptographic schemes is RSA (Rivest-Shamir-Adleman), which was devised back in 1976. Basically, every participant of a public key cryptography system like RSA has both a public key and a private key. To send a secure message, data is encoded as a large number and scrambled using the public key of the person you want to send it to. The person on the receiving end can decrypt it with their private key. In RSA, the public key is a large number, and the private key is its prime factors. With Shor’s algorithm, a quantum computer with enough qubits could factor large numbers. For RSA, someone with a quantum computer can take a public key and factor it to get the private key, which allows them to read any message encrypted with that public key. This ability to factor numbers breaks nearly all modern cryptography. Since cryptography is what provides pervasive security for how we communicate and share information online, this has significant implications.
Theoretically, if an adversary were to gain control of a quantum computer, they could create total chaos. They could create cryptographic certificates and impersonate banks to steal funds, disrupt Bitcoin, break into digital wallets, and access and decrypt confidential communications. Some liken this to Y2K. But, unlike Y2K, there’s no fixed date as to when existing cryptography will be rendered insecure. Researchers have been preparing and working hard to get ahead of the curve by building quantum-resistant cryptography solutions.
When will a quantum computer be built that is powerful enough to break all modern cryptography? By some estimates, it may take 10 to 15 years. Companies and universities have made a commitment to innovation in the field of quantum computing, and progress is certainly being made. Unlike classical computers, quantum computers rely on quantum effects, which only happen at the atomic scale. To instantiate a qubit, you need a particle that exhibits quantum effects like an electron or a photon. These particles are extremely small and hard to manage, so one of the biggest hurdles to the realization of quantum computers is how to keep the qubits stable long enough to do the expensive calculations involved in cryptographic algorithms.
Both quantum computing and quantum-resistant cryptography are works in progress
It takes a long time for hardware technology to develop and mature. Similarly, new cryptographic techniques take a long time to discover and refine. To protect today’s data from tomorrow’s quantum adversaries, we need new cryptographic techniques that are not vulnerable to Shor’s algorithm.
The National Institute of Standards and Technology (NIST) is leading the charge in defining post-quantum cryptography algorithms to replace RSA and ECC. There is a project currently underway to test and select a set of post-quantum computing-resistant algorithms that go beyond existing public-key cryptography. NIST plans to make a recommendation sometime between 2022 and 2024 for two to three algorithms for both encryption and digital signatures. As Dustin Moody, NIST mathematician points out, the organization wants to cover as many bases as possible: “If some new attack is found that breaks all lattices, we’ll still have something to fall back on.”
We’re following closely. The participants of NIST have developed high-speed implementations of post-quantum algorithms on different computer architectures. We’ve taken some of these algorithms and tested them in Cloudflare’s systems in various capacities. Last year, Cloudflare and Google performed the TLS Post-Quantum Experiment, which involved implementing and supporting new key exchange mechanisms based on post-quantum cryptography for all Cloudflare customers for a period of a few months. As an edge provider, Cloudflare was well positioned to turn on post-quantum algorithms for millions of websites to measure performance and use these algorithms to provide confidentiality in TLS connections. This experiment led us to some useful insights around which algorithms we should focus on for TLS and which we should not (sorry, SIDH!).
More recently, we have been working with researchers from the University of Waterloo and Radboud University on a new protocol called KEMTLS, which will be presented at Real World Crypto 2021. In our last TLS experiment, we replaced the key negotiation part of TLS with quantum-safe alternatives but continued to rely on digital signatures. KEMTLS is designed to be fully post-quantum and relies only on public-key encryption.
On the implementation side, Cloudflare team members including Armando Faz Hernandez and visiting researcher Bas Westerbaan have developed high-speed assembly versions of several of the NIST finalists (Kyber, Dilithium), as well as other relevant post-quantum algorithms (CSIDH, SIDH) in our CIRCL cryptography library written in Go.
Post-quantum security, coming soon?
Everything that is encrypted with today’s public key cryptography can be decrypted with tomorrow’s quantum computers. Imagine waking up one day, and everyone’s diary from 2020 is suddenly public. Although it’s impossible to find enough storage to record keep all the ciphertext sent over the Internet, there are current and active efforts to collect a lot of it. This makes deploying post-quantum cryptography as soon as possible a pressing privacy concern.
Cloudflare is taking steps to accelerate this transition. First, we endeavor to use post-quantum cryptography for most internal services by the end of 2021. Second, we plan to be among the first services to offer post-quantum cipher suites to customers as standards emerge. We’re optimistic that collaborative efforts among NIST, Microsoft, Cloudflare, and other computing companies will yield a robust, standards-based solution. Although powerful quantum computers are likely in our future, Cloudflare is helping to make sure the Internet is ready for when they arrive.


Physicists from MIPT and the Russian Quantum Center have developed an easier method to create a universal quantum computer using multilevel quantum systems (qudits), each one of which is able to work with multiple "conventional" quantum elements – qubits.
Professor Vladimir Man'ko, Aleksey Fedorov and Evgeny Kiktenko have published the results of their studies of multilevel quantum systems in a series of papers in Physical Review A, Physics Letters A, and also Quantum Measurements and Quantum Metrology.
"In our studies, we demonstrated that correlations similar to those used for quantum information technologies in composite quantum systems also occur in non-composite systems – systems which we suppose may be easier to work with in certain cases. In our latest paper we proposed a method of using entanglement between internal degrees of freedom of a single eight-level system to implement the protocol of quantum teleportation, which was previously implemented experimentally for a system of three two-level systems," says Vladimir Man'ko.
Quantum computers, which promise to bring about a revolution in computer technology, could be built from elementary processing elements called quantum bits – qubits. While elements of classical computers (bits) can only be in two states (logic zero and logic one), qubits are based on quantum objects that can be in a coherent superposition of two states, which means that they can encode the intermediate states between logic zero and one. When a qubit is measured, the outcome is either a zero or a one with a certain probability (determined by the laws of quantum mechanics).
In a quantum computer, the initial condition of a particular problem is written in the initial state of the qubit system, then the qubits enter into a special interaction (determined by the specific problem). Finally, the user reads the answer to the problem by measuring the final states of the quantum bits.
Quantum computers will be able to solve certain problems that are currently far beyond the reach of even the most powerful classical supercomputers. In cryptography, for example, the time required for a conventional computer to break the RSA algorithm, which is based on the prime factorization of large numbers, would be comparable to the age of the universe. A quantum computer, on the other hand, could solve the problem in a matter of minutes.
However, there is a significant obstacle standing in the way of a quantum revolution – the instability of quantum states. Quantum objects that are used to create qubits – ions, electrons, Josephson junctions etc. can only maintain a certain quantum state for a very short time. However, calculations not only require that qubits maintain their state, but also that they interact with one another. Physicists all over the world are trying to extend the lifespan of qubits. Superconducting qubits used to "survive" only for a few nanoseconds, but now they can be kept for milliseconds before decoherence – which is closer to the time required for calculations.
In a system with dozens or hundreds of qubits, however, the problem is fundamentally more complex.
Man'ko, Fedorov, and Kiktenko began to look at the problem from the other way around – rather than try to maintain the stability of a large qubit system, they tried to increase the dimensions of the systems required for calculations. They are investigating the possibility of using qudits rather than qubits for calculations. Qudits are quantum objects in which the number of possible states (levels) is greater than two (their number is denoted by the letter D). There are qutrits, which have three states; ququarts, which have four states, etc. Algorithms are now actively being studied in which the use of qudits could prove to be more beneficial than using qubits.
"A qudit with four or five levels is able to function as a system of two "ordinary" qubits, and eight levels is enough to imitate a three-qubit system. At first, we saw this as a mathematical equivalence allowing us to obtain new entropic correlations. For example, we obtained the value of mutual information (the measure of correlation) between virtual qubits isolated in a state space of a single four-level system," says Fedorov.
He and his colleagues demonstrated that on one qudit with five levels, created using an artificial atom, it is possible to perform full quantum computations—in particular, the realization of the Deutsch algorithm. This algorithm is designed to test the values of a large number of binary variables.
It can be called the fake coin algorithm: imagine that you have a number of coins, some of which are fake – they have the same image on the obverse and reverse sides. To find these coins using the "classical method", you have to look at both sides. With the Deutsch algorithm, you "merge" the obverse and reverse sides of the coin and you can then see a fake coin by only looking at one side.
The idea of using multilevel systems to emulate multi-qubit processors was proposed earlier in the work of Russian physicists from the Kazan Physical-Technical Institute. To run a two-qubit Deutsch algorithm, for example, they proposed using a nuclear spin of 3/2 with four different states. In recent years, however, experimental progress in creating qudits in superconducting circuits has shown that they have a number of advantages.
However, superconducting circuits require five levels: the last level performs an ancillary role to allow for a complete set of all possible quantum operations.
"We are making significant progress, because in certain physical implementations, it is easier to control multilevel qudits than a system of the corresponding number of qubits, and this means that we are one step closer to creating a full-fledged quantum computer. Multilevel elements offer advantages in other quantum technologies too, such as quantum cryptography," says Fedorov.
More information: E.O. Kiktenko, A.K. Fedorov, O.V. Man'ko, and V.I. Man'ko. Multilevel superconducting circuits as two-qubit systems: Operations, state preparation, and entropic inequalities // Physical Review A arxiv.org/abs/1411.0157
E.O. Kiktenko, A.K. Fedorov, A.A. Strakhov, and V.I. Man'ko. Single qudit realization of the Deutsch algorithm using superconducting many-level quantum circuits // Physics Letters A 379, 1409–1413 (2015), arxiv.org/abs/1503.01583
E.O. Kiktenko, A.K. Fedorov, and V.I. Man'ko. Teleportation in an indivisible quantum system // Quantum Measurements and Quantum Metrology 3, 13–19 (2016), arxiv.org/abs/1512.05168
Provided by Moscow Institute of Physics and Technology


Post-quantum cryptography, also called quantum encryption, is the development of cryptographic systems for classical computers that are able to prevent attacks launched by quantum computers.
During the 1980s, scientists speculated that if computers could take advantage of the unique properties of quantum mechanics, they could perform complicated computations much faster than classical, binary computers. It quickly became clear that a quantum computer, taking advantage of quantum properties such as superposition and entanglement, could complete certain types of complex calculations in a matter of hours -- even though it would take a classical computer several years to complete the same calculation.
During the 1990s, after mathematician Peter Shor successfully demonstrated that a theoretical quantum computer could easily break the algorithm used for public key encryption (PKE), cryptographers around the world began to explore what a post-quantum cryptography system would look like. As of this writing, standards for how to implement post-quantum encryption are still emerging.
Pre-quantum vs. quantum vs. post-quantum cryptography
Quantum computers use the laws of quantum mechanics to process information in quantum bits (qubits). Because each qubit can be a combination of 0s and 1s, a quantum computer can process variables exponentially faster than a classical, binary computer.
Pre-quantum cryptography uses a specific type of cipher called an algorithm to transform human-readable data into secret code. The challenge of pre-quantum cryptography is to make encryption ciphers easy to understand but difficult to reverse engineer.
In contrast, quantum cryptography relies on the physical properties of atoms and uses geometric ciphers to transform human-readable data into unbreakable secret code. A major challenge of post-quantum cryptography is that quantum physics is still an emerging scientific field of study, and prototypes for quantum computers are very expensive to build and operate.
The quest for quantum-resistant algorithms
In 2016, researchers from MIT and the University of Innsbruck built a small quantum computer that was able to successfully implement Shor's algorithm and find the factors for the number 15. Once researchers were able to demonstrate that Shor's quantum algorithm could be used to return the correct factors with a confidence level that exceeded 99%, it quickly became clear that the world's most widely used cryptographic methods could be broken by a quantum computer.
In 2016, the National Institute of Standards and Technology (NIST) began to seek out submissions for algorithms that could potentially replace public key encryption, key encapsulation mechanisms (KEMs) and digital signatures.
In response, mathematicians and programmers began experimenting with a wide variety of strategies to replace integer factorization as well as the discrete logarithmic problems used in the Rivest-Shamir-Adleman (RSA) algorithm, Elliptic Curve Digital Signature Algorithm (ECDSA), Elliptic Curve Diffie–Hellman Key Exchange (ECDH) and Digital Signature Algorithm (DSA) cryptosystems.
Google's experiments in post-quantum cryptography, for example, involve coupling a classical elliptic curve algorithm with a post-quantum algorithm. The idea is that even if the quantum cryptography turns out to be breakable, the addition of an elliptic curve algorithm will still provide a measure of security.
Other popular strategies for creating quantum-resistant algorithms include the use of lattice, code-based and multivariate schemes. As of this writing, lattice schemes seem to be the most promising, perhaps because it's extremely difficult to calculate the shortest vector of a large lattice when the shortest vector is quantum and can exist in more than one dimension.
The future of post-quantum cryptography
The algorithms that support encryption today, including public key cryptography, are still considered to be safe for e-commerce because while quantum computing is real, the technology is expensive and use cases have their roots in scientific and government research. The race is on, however, among researchers who are trying to find a post-quantum encryption that works and researchers who are trying to break RSA and similar cryptosystems with quantum algorithms.
Many experts believe that we will reach quantum supremacy within nine or 10 years, at which time RSA and similar asymmetrical algorithms will no longer be able to protect sensitive data. This is why NIST is moving so aggressively to create a standard for post-quantum encryption.
Experts recommend that while NIST is busy evaluating the effectiveness of proposed standards for post-quantum cryptography, organizations use the next couple years to create a reference index for those applications that use encryption. Organizations should also keep track of the public and third-party encryption libraries. Once the strategies for implementing post-quantum cryptography have matured and a standard has been approved, the index can be used to develop a plan for how the organization will either replace or upgrade those applications that require cryptography.
Post-quantum cryptography vs. quantum key distribution
Post-quantum cryptography should not be confused with quantum key distribution (QKD). QKD simply allows a secret cryptographic key to be shared between two remote parties in such a way that key interception can be easily detected.


It seems that diamonds grown in a lab will have many roles to play in the electronics and engineering of the future. This could be because these precious stones contain (necessary) defects, often worked into the diamonds to order.
The defects are created when a non-carbon atom takes the place of a carbon atom in the orderly molecular lattice that normally makes a diamond. Nitrogen vacancies (NVs), for example, have drawn some attention due to their potential in diagnostics, and their ability to emit red light when green light hits them, which has potential analytical value.
NVs have recently demonstrated the ability to assess the flow of electrons across tiny strips of graphene with great accuracy and sensitivity. This may be important, particularly if graphene realizes its promise as the superconductor of the future.
Diamonds in Quantum Computing
Diamonds with vacancies could be used to transmit or store data at the quantum level. In other words, they could be used as repeaters across networks between computers, all of which would be…quantum in nature.
Unfortunately, NVs have relatively poor optical qualities, meaning that their applications may be limited. For example, nitrogen vacancies may degrade the quality or integrity of quantum data over distance. This is a shame, as NVs also have long lifespans.
Therefore, a team of scientists at Princeton (in collaboration with others from the Gemological Institute of America in New York and the UK company, Element Six) decided to investigate the potential of alternative vacancy types in the transfer and storage of quantum bits (or qubits).
Previous work indicated that silicon vacancies (SiVs) significantly improved optical properties compared to NVs. However, SiVs also have a charge (namely 2+), which may impact their interactions with protons and electrons that are necessary for quantum data-transmission. More specifically, the charged vacancies, from past research, showed that SiVs did not hold coherence among the phonons (represent ‘noise’ in a quantum data system) for the required lengths of time.
This quantum-capable wafer may be only so useful without the ability to network with other quantum processors. (Source: Steve Jurvetson @ flickr)
Neutral Silicon Vacancies: Production and Testing
The team hypothesized that SiVs without a charge or neutral SiVs (SiV0s) could solve these problems.
Therefore, they commissioned the company, Element Six, to synthesize diamonds, which the investigators then treated with heat to implant silicon ions into the material.
This process required repeated tweaking and tuning before the successful production of diamonds with SiV0s. These vacancies exhibited a coherence time of nearly 1 second, and spin-lattice relaxation within approximately 1 minute.
These favorable properties were accompanied by desirable optical linewidths and excellent light-emission specifications. The team also reported that these attributes allowed for successful quantum entanglement; in other words, super-secure data transmission between two quantum sources.
The group was confident that their SIV0s would be capable of repeating qubits (which are often encoded into photons) across a network.
The researchers have also proposed further studies, in which a system will be designed to test this concept out. The project would likely include a simple quantum computer or computer with SiV0s as the data interface.
On the other hand, the successful production of SiV0s, which may be able to transfer quantum data, is a considerable achievement.
This study may be the first step towards the establishment of quantum networks that depend on diamonds with silicon vacancies. In addition, the solid medium may have advantages over others (e.g., in conventional fiber-optic cables) in terms of quantum data integrity. Furthermore, this SiV0s may also be useful for quantum data storage.
On the other hand, SiV0s do not have the lifespan associated with NVs. This may be a problem for the future of quantum computing.
Vacancies cause the light within diamonds to act slightly differently compared to that of flawless stones. (Source: de Leon lab, Princeton)
Vacancies within diamonds have been vilified for centuries, as merchants and jewelers were aware of their flaws due to the colored light they caused gems to reflect.
However, scientists have found much to value in these so-called defects. They can be exploited to produce cutting-edge optical and nanoscopic diagnostic tools.
In addition, as demonstrated in a recent issue of the journal Science, certain vacancies can confer the data-repeating abilities necessary for true, networked quantum computing. Therefore, this study may help unlock the potential of quantum processing, which is the next step towards greater complexity and flexibility in computing.
On the other hand, scientists will have to find a way to make the silicon vacancies in question last as long as their nitrogen counterparts previously did.
Top Image: A perfect diamond. (Source: http://pngimg.com)
Implanting diamonds with flaws to provide key technology for quantum communications, 2018, Princeton News, https://www.princeton.edu/news/2018/07/05/implanting-diamonds-flaws-provide-key-technology-quantum-communications , (accessed 10 Jul. 18)
B. C. Rose, et al. (2018) Observation of an environmentally insensitive solid-state spin defect in diamond. Science. 361:(6397). pp.60-63.
Graphene is the New Silicon? – A Closer Look at the Most Likely Next-Generation Superconductor, 2017, Evolving Science, https://www.evolving-science.com/information-communication-computer-science-technology/graphene-new-silicon-closer-look-most-likely-next-generation-superconductor-00415 , (accessed on 10 Jul. 18)


Binary refers to any system that uses two alternative states, components, conditions or conclusions. The binary, or base 2, numbering system uses combinations of just two unique numbers, i.e., zero and one, to represent all values, in contrast with the decimal system (base 10), which uses combinations of ten unique numbers, i.e., zero through nine.
Virtually all electronic computers are designed to operate internally with all information encoded in binary numbers. This is because it is relatively simple to construct electronic circuits that generate two distinct voltage levels (i.e., off and on or low and high) to represent zero and one. The reason is that transistors and capacitors, which are the fundamental components of processors (the logic units of computers) and memory, generally have only two distinct states: off and on.
The values of bits are stored in various ways, depending on the medium. For example, the value of each bit is stored as an electrical charge in a single capacitor within a RAM (random access memory) chip. It is stored as the magnetization of a microscopic area of magnetic material on a platter in a hard disk drive (HDD) or on a floppy disk. It is stored along the spiral track on an optical disk as a change from a pit to the surface or from the surface to a pit (representing a one) and as no change (representing a zero).
Computers are almost always designed to store data and execute instructions in larger and more meaningful units called bytes, although they usually also provide ways to test and manipulate single bits. Bytes are abbreviated with an upper case B, and bits are abbreviated with a lower case b. The number of bits in a byte varied according to the manufacturer and model of computer in the early days of computing, but today virtually all computers use bytes that consist of eight bits.
Whereas a bit can have only one of two values, an eight-bit byte can have any of 256 possible values, because there are 256 possible permutations (i.e., combinations of zero and one) for eight consecutive bits (i.e., 28). Thus, an eight-bit byte can represent any unsigned integer from zero through 255 or any signed integer from -128 to 127. It can also represent any character (i.e., letter, number, punctuation mark or symbol) in a seven-bit or eight-bit character encoding system (such as ASCII, the default character encoding used on most computers).
The number of bits is often used to classify generations of computers and their components, particularly CPUs (central processing units) and busses and to provide an indication of their capabilities. However, such terminology can be confusing or misleading when used in an imprecise manner, which it frequently is.
For example, classifying a computer as a 32-bit machine might mean that its data registers are 32 bits wide, that it uses 32 bits to identify each address in memory or that its address buses or data buses of that size. A register is a very small amount of very fast memory that is built into the CPU in order to speed up its operations by providing quick access to commonly used values. Whereas using more bits for registers makes computers faster, using more bits for addresses enables them to support larger programs.
A bus is a set of wires that connects components within a computer, such as the CPU and the memory. A 32-bit bus transmits 32 bits in parallel (i.e., simultaneously rather than sequentially).
Although CPUs that treat data in 32-bit chunks (i.e., processors with 32-bit registers and 32-bit memory addresses) still constitute the personal computer mainstream, 64-bit processors are common in high-performance servers and are now being used in an increasing number of personal computers as well.
The rate of data transfer in computer networks and telecommunications systems is referred to as the bit rate or bandwidth, and it is usually measured in terms of some multiple of bits per second, abbreviated bps, such as kilobits, megabits or gigabits (i.e., billions of bits) per second.
A bitmap is a method of storing graphics (i.e., images) in which each pixel (i.e., dot that is used to form an image on a display screen) is stored as one or several bits. Graphics are also often described in terms of bit depth, which is the number of bits used to represent each pixel. A single-bit pixel is monochrome (i.e., either black or white), a two-bit pixel can represent any of four colors (or black and white and two shades of gray), an eight bit pixel can represent 256 colors and 24-bit and 32-bit pixels support highly realistic color which is referred to as true color.
The word bit was invented in the latter half of the 1940s by John W. Tukey (1915-2000), an eminent statistician, while working at Bell Labs (the research arm of AT&T, the former U.S. telecommunications monopoly). He coined it as a contraction of the term binary digit and as a handier alternative to bigit or binit. Tukey also coined the word software.
The term bit was first used in an influential publication by Claude E. Shannon (1916-2001), also while at Bell Labs, in his seminal 1948 paper A Mathematical Theory of Communication. Shannon, widely regarded as the father of information theory, developed a theory that for the first time treated communication as a rigorously stated mathematical problem and provided communications engineers with a technique for determining the capacities of communications channels in terms of of bits.
Although the bit has been the smallest unit of storage used in computing so far, much research is being conducted on qubits, the basic unit of information in quantum computing (which is based on phenomena that occur at the atomic and subatomic levels). Qubits hold an exponentially greater amount of information than conventional bits.
Created March 4, 2005. Updated April 5, 2006.