Their recent report* is a major step towards a capability to capture, cool and manipulate individual atoms of erbium, an element with unique optical properties that promises highly sensitive nanoscale force or magnetic sensors, as well as single-photon sources and amplifiers at telecommunications wavelengths. It also may have applications in quantum computing devices.
The strongly counterintuitive technique of “laser cooling” to slow down atoms to very low speeds—temperatures close to absolute zero—has become a platform technology of atomic physics. Laser cooling combined with specially arranged magnetic fields—a so-called magneto-optical trap (MOT)—has enabled the creation of Bose-Einstein condensates, the capture of neutral atoms for experiments in quantum computing and ultra-precise time-keeping and spectroscopy experiments. The technique originally focused on atoms that were only weakly magnetic and had relatively simple energy structures that could be exploited for cooling, but two years ago a NIST team showed that the far more complex energy structures of erbium, a strongly magnetic element, also could be manipulated for laser cooling.
The typical MOT uses a combination of six tuned laser beams converging on a point that is in a low magnetic field but surrounded by stronger fields. Originally, the lasers were tuned near a strong natural energy oscillation or resonance in the atom, a condition that provides efficient cooling but to only moderately low temperatures. In the new work, the research team instead used much gentler forces applied through a very weak resonance in order to bring erbium atoms to within a few millionths of a degree of absolute zero. Such weak resonances are only available in atoms with complex energy structures, and previously have been used only with a select group of non-magnetic atoms. When a strongly magnetic atom like erbium is used, the combination of strong magnetic forces and weak absorption of laser photons makes a traditional MOT unstable.
To beat this, the NIST/UM team turned classic MOT principles on their heads. Rather than shifting the laser frequency towards the red end of the spectrum—to impact fast, high-temperature atoms more than slow, cold ones—they shifted the laser towards the blue side to take advantage of the effects of the magnetic field on the highly magnetic erbium. Magnetism holds the atoms stably trapped while the lasers gently pushed them against the field, all the while extracting energy and cooling them. The delicate balancing act not only cools and traps the elusive erbium atoms, it does it more efficiently. The team’s modified trap design uses only a single laser and can cool erbium atoms to within two millionths of a degree of absolute zero. By contrast, a conventional MOT only brings rubidium atoms to about one ten-thousandth of a degree.
Erbium commonly is used in optical communications components for its convenient magneto-optical properties. The new trapping technique raises the possibility of using erbium and similar lanthanide elements for unique nanoscale magnetic field detectors, atomic resolution metrology, optical computing systems and quantum computing.
Michael Baum | EurekAlert!
NASA detects solar flare pulses at Sun and Earth
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16.11.2017 | University of California - Santa Cruz
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
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The latest news from academia, regulators
research labs and other things of interest
Posted: Apr 01, 2013
A solid state ultrafast logic gate on a photon
(Nanowerk News) If you could peek at the inner workings of a computer processor you would see billions of transistors switching back and forth between two states. In optical communications, information from the switches can be encoded onto light, which then travels long distances through glass fiber. Researchers at the Joint Quantum Institute and the Department of Electrical and Computer Engineering are working to harness the quantum nature of light and semiconductors to expand the capabilities of computers in remarkable ways.
All computers, even the future quantum versions, use logic operations or “gates,” which are the fundamental building blocks of computational processes. JQI scientists, led by Professor Edo Waks, have performed an ultrafast logic gate on a photon, using a semiconductor quantum dot. This research is described in the March 31 Advance Online Publication of Nature Photonics ("A quantum logic gate between a solid-state quantum bit and a photon").
Illustration of a CNOT gate with a semiconductor quantum dot and a photon.
Photons are a proven transit system for information. In quantum devices, they are the ideal information carriers that relay messages between quantum bits (qubits) such as neutral atoms, ion traps, superconducting circuits, nitrogen vacancy centers, and of course the device used here: quantum dots. A quantum dot (QD) is a semiconductor structure that acts like an atom. This means it has allowed energy levels that can be populated and even shifted around using lasers and magnetic fields. Quantum dots are an attractive platform for quantum processing because they live inside a semiconductor material, thus the technology for integration with modern electronics already exists.
The Waks team has implemented a conditional logic gate called a Controlled-NOT (CNOT). Here’s how a generic CNOT gate works: if a control qubit is in what we will call state 1, then the gate flips the state of a second qubit. If the control qubit is in state 0, nothing happens.
Waks explains the importance of this gate, “Although this logic operation sounds simple, the CNOT gate has the important property that it is universal, which means that all computational algorithms can be performed using only this simple operation. This powerful gate can thus be seen as important step towards implementing any quantum information protocol.”
In this experiment, a quantum dot plays the role of the control qubit. The second qubit is a photon that has two polarization states. Polarization can be thought of as an orientation of the traveling light waves. For instance, polarized sunglasses can shield your eyes from light having certain orientations. Here, photons can be oriented horizontally or vertically with respect to a defined direction. Just like energy levels for a quantum dot constitute a qubit, the two available polarizations make up a photonic qubit.
Light is injected into a photonic crystal cavity (see sidebar in gallery) containing a quantum dot. Quantum dots have been trapped in photonic crystals before, but the difference here is an added large external magnetic field. The magnetic field shifts around the energy levels of the quantum dot enabling it to simultaneously act as both a stable qubit and a highly efficient photon absorber. Due to the unique energy level structure of the system, changing the qubit state of the quantum dot can render it completely invisible to the light.
This property makes the CNOT gate possible (see figure above). Light trapped in a cavity that does not see a QD (QD in qubit state 1) will eventually leak out, with its polarization flipped. However, if the quantum dot is in qubit state 0, the light is strongly modified such that incoming and outgoing polarizations actually remain the same. In this case the photonic qubit is not flipped.
A sensitive camera collects a fraction of the light that leaks back out of the cavity after its polarization is analyzed using special optics. Thus, the team can see if a photon’s polarization was flipped by the QD. The state of the QD qubit is not random: the team controls it. Another key feature of this protocol is that the photons are from an external laser and are not intrinsically connected to the QD through absorption/emission processes.
“Using an external photon source has an advantage that the quantum dot state is not destroyed during the process. Currently, we use a strongly attenuated laser as the photon source, but eventually this can be replaced with true single photon sources,” says lead author Dr. Hyochul Kim.
This quantum dot-photon gate happens in a flash--picosecond or 1/ trillionth of a second. Ultrafast gates are important when increasing the number of qubits and operations so that a calculation completes before the system’s quantum behavior is lost. (This is called decoherence--scientists can shield the qubit from the disruptive environment but every so often something sneaks in and destroys the quantum states.)
The team’s proof-of-principle gate demonstration paves the way for the next generation of devices that will improve light collection and QD qubit coherence times. “To improve coherence time, we need to trap the electron or hole in the quantum dot and use their spin as a qubit. This is more challenging, and we are currently working on this,” Kim says.
Additionally, they will use truly single photons as the light source. “Quantum dots are also excellent single photon sources. We consider such a system where single photons are periodically emitted from the neighbor quantum dot, which are then connected to logic devices on the same semiconductor chip,” adds Kim.


May 12, 2011
A small firm based in Canada that aims to build a commercially viable quantum computer has shown that an important part of its technology works. D-Wave Systems, which was spun-out of the University of British Columbia in 1999, has shown that a technique called quantum annealing can be used to make eight coupled quantum bits – or qubits – find their ground state. According to the firm’s chief technology officer Geordie Rose, the announcement is the first of several scientific results that D-Wave will be unveiling – including one that he claims is "mind blowing".
Based in Vancouver, D-Wave was set up with the aim of creating a quantum computer that uses loops of superconducting wire as qubits. As the electrical current circulating within such a "flux qubit" is quantized, the two lowest states (i.e. electrons travelling clockwise and anticlockwise) can be assigned data values of "0" or "1". The magnetic field associated with the currents is also quantized – pointing up and down for currents moving in opposite directions – and can be flipped using an external magnetic field.
Resisting heat and noise
Quantum computers could outperform a classical computer at some tasks – at least in principle – thanks to two key quantum properties. These are that a qubit can be in a superposition of two or more quantum states and that two or more qubits can be entangled. But the big challenge for D-Wave – and for everyone else trying to build a quantum computer – is how to create qubits and computing processes that are resistant to the destructive effects of heat and noise.
Using flux qubits is attractive in that quest because they are macroscopic structures that can be created using semiconductor-manufacturing processes and can be controlled using applied currents and voltages. A downside is that they have a multitude of quantum states, not just two. The task for D-Wave is how to place each qubit in a well-defined and useful quantum state without it being corrupted by heat or noise – essentially the analogue of writing data to a classical computer.
The method chosen by the firm to do this is called "quantum annealing" – and now D-Wave has shown that it can use this technique to place eight coupled qubits into the appropriate lowest energy state. The researchers began with eight superconducting flux qubits within one of D-Wave’s integrated circuits. These contain 128 flux qubits arranged into 16 units of eight. The system is then cooled to a temperature of 10 mK, which puts each qubit into a superposition of two quantum states with identical energy, i.e. current circulating anticlockwise (spin-up) and clockwise (spin-down).
Raising the barrier
This superposition is not, however, particularly useful and the next step is to manipulate each qubit into a pure spin-up or spin-down state. Each loop is broken by a structure containing two Josephson junctions and a magnetic coil. When a current is applied to the coil, an energy barrier rises between the spin-up and spin-down states. In a classical system, the loop would be forced into either the up or down state and could hop between states by absorbing heat from the surroundings. A qubit however, remains in a superposition of up and down as long as the barrier rises slowly enough.
Each qubit has a second magnetic coil, which is used to "tip" the qubit into the desired pure state. If the field is applied in the up direction, for example, the energy of the spin-up state drops below that of the spin-down state, thereby making it more likely that the qubit will become pure spin-up. The problem facing D-Wave is that this transition occurs both by quantum-mechanical tunnelling and by absorbing heat (thermal excitation). Thermal excitation destroys the quantum nature of the qubit, and so must be avoided during quantum annealing.
The two processes can be distinguished by raising the barrier until both tunnelling and heat-driven transitions stop (the qubit "freezes") – and then repeating this process at different temperatures. The research team found that below about 45 mK, freezing is affected primarily by barrier height and not temperature, which is what is expected if annealing occurs by tunnelling alone.
The team then showed that it could anneal a unit of eight qubits. The researchers did this by adjusting the interactions between the qubits to simulate a 1D chain of magnets in which each qubit wants to point in the same direction as its two neighbours. The qubit at the right-hand end of the chain is set in the up direction and the qubit at the left-hand end in the down direction. The six qubits in the middle are then allowed to orient their spins according to that of their neighbours. The result is a "frustrated" ferromagnetic arrangement in which two neighbours must have opposing spins.
Finally, the qubits are all tilted in the same direction while the barrier is raised. This should result in the system moving towards one specific arrangement of frustrated spins – the ground state. Again, below about 45 mK, the system found its way to the ground state in a manner consistent with the spins flipping because of quantum-mechanical tunnelling, not thermal activation. "We're very excited to see the remarkable agreement between what quantum mechanics predicts and what we see in these circuits," says D-Wave’s Mark Johnson, who was lead scientist on the project.
Finding the ground state of an eight-spin system is a simple quantum calculation and therefore the D-Wave team has shown that its combination of hardware and annealing process is capable of the job.
"Important" first step
"This is the first time that the D-Wave system has been shown to exhibit quantum mechanical behaviour," says William Oliver of the Massachusetts Institute of Technology, who was not involved in the research. Oliver told physicsworld.com that when combined with D-Wave’s ability to control precisely important parameters of the qubits, this latest work is "a technical achievement and an important first step".
Looking beyond quantum computing, David Feder of the University of Calgary also sees the system as an effective quantum simulation of how electron spins interact in magnetic materials. "This work describes a nice approach to simulating the (ferromagnetic or antiferromagnetic) quantum Ising model, and this is interesting in its own right," explains Feder. "I think that there is a lot of promise in the D-Wave architecture for simulating frustrated magnetic systems, and maybe more general strongly correlated systems, and this will benefit everyone. So, to me, it is a good step in the right direction."
D-Wave currently employs about 60 scientists and engineers, of whom about 20 work on developing algorithms and 40 work on building hardware, according to Rose. This latest research was carried out by 25 of D-Wave’s employees along with researchers at the University of Agder in Norway and Simon Fraser University in Canada.
"This is the first time we’ve been able to open up the black box and show how [D-Wave’s devices] are harnessing quantum mechanics in solving problems," says Rose. He told physicsworld.com that the firm now plans to do similar quantum-annealing experiments involving much larger numbers of qubits. He also says that the researchers will apply the process to "real problems" such as machine learning and artificial technology. Rose is adamant that D-Wave’s systems could be used in commercial settings as well as for doing basic research in quantum computing. "Our sales team is out selling at the moment," he says.
According to Rose, the company will soon publish a number of journal papers about its research. However, he was unable to provide more details because the work is currently being peer-reviewed.


lasers made easy
Technology Research News
Tight control of photons in the form of
laser beams is a key ingredient in technologies ranging from the Internet
and long-distance telephone lines to CD and DVD players. Tightly controlling
atoms in similar ways could also have far-reaching impact.
For several years researchers have been able to make groups of atoms behave
like one atomic entity by chilling certain gases to just above absolute
zero, and they have been able to produce beams of atoms by shining lasers
at these Bose-Einstein Condensates.
But the process requires a complicated combination of laser beams, magnetic
fields and radio waves, and the cumbersome laboratory equipment involved
makes it difficult to study coherent matter, let alone make useful devices
out of it.
A team of researchers at the Georgia Institute of Technology, however,
has sidestepped the problem by finding a way to make condensed gas using
Atom lasers could be used to deposit material atom by atom on a surface
to, for instance, produce extremely fine lines on a computer chip. They
could also make extremely sensitive measuring devices because atom waves,
like light waves, can interfere with each other and the interference patterns
are affected by tiny changes in forces like acceleration and gravity.
Condensed atoms could also open the way for quantum mechanically linking
thousands of atoms, which could yield extraordinarily powerful quantum
"Researchers have been trying to achieve atomic Bose-Einstein Condensates
using all-optical techniques for about 15 years," said Michael Chapman,
an assistant professor of physics at Georgia Tech. "What we showed is
that not only is it possible, it's downright easy. Better yet, the technique
is faster than the magnetic trapping techniques," he said.
The researchers trapped 30 million rubidium atoms in three intersecting
low-power laser beams, then transferred the atoms to a trap made of two
intersecting high-power laser beams. The transfer left 2 million atoms
in the second laser trap. The researchers allowed many of those atoms
to evaporate out of the trap, leaving 660,000 much colder atoms, then
decreased the power of the lasers, which caused a second round of evaporative
The researchers were able to make this last step happen in about 2 1/2
seconds, which was fast enough for the remaining 3,500 atoms to form a
"This is a marvelous piece of work. It is significant because it highlights
an efficient and robust route to the production of Bose-Einstein condensed
atoms, or atom lasers," said Mark Kasevich, an associate professor of
applied physics at Yale University.
Previous Bose-Einstein Condensate experiments trapped atoms with large
magnets and cooled them by generating a radio frequency electric field,
said Michael G. Moore, a physicist at the Harvard-Smithsonian Center for
The Georgia Tech experiment replaced both with a commercial carbon dioxide
laser. "The increase in simplicity is therefore enormous. The decrease
in cost is probably quite significant as well," he said. The all-optical
techniques for producing Bose-Einstein Condensates is a significant step
toward using condensed matter in practical devices, said Moore.
The Georgia Tech researchers plan to experiment with using the laser-produced
Bose-Einstein Condensates for quantum computing, said Chapman.
One problem in quantum computing is information transfer. Atoms are useful
for storing and manipulating quantum information but are difficult to
transport, while photons are hard to store but could be used to transfer
quantum information within and between quantum computers. "A particularly
intriguing possibility is to combine the condensates with optical cavities,
which are two facing mirrors that trap photons, to exchange quantum information
between the photons and atomic condensates," Chapman said.
It it is likely to be more than 10 years before Bose-Einstein Condensates
are used in practical applications, said Chapman.
Chapman's research colleagues were Murray B. Barrett and Jacob A. Sauer
of Georgia Tech. They published the research in the July 2, 2001 issue
of the journal Physical Review Letters. The research was funded by the
National Security Agency and the Advanced Research and Development Activity,
which is a joint NSA-Department of Defense funding organization.
Timeline: >10 years
TRN Categories: Optical Computing, Optoelectronics and
Photonics; Quantum Computing
Story Type: News
Related Elements: Technical paper, "All-Optical Formation
of an Atomic Bose-Einstein Condensate," Physical Review Letters, July
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Molecule makes mini memory
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Credit: Courtesy of F. Brandão
The Power of Entanglement: A Conversation with Fernando Brandão
Computers are a ubiquitous part of modern technology, utilized in smartphones, cars, kitchen appliances, and more. But there are limits to their power. New faculty member Fernando Brandão, the Bren Professor of Theoretical Physics, studies how quantum computers may someday revolutionize computing and change the world's cryptographic systems.
What do you do?
My research is in quantum information science, a field which seeks to merge two of the biggest discoveries of the last century: quantum mechanics and computer science. Particularly, I am interested in studying quantum entanglement. Entanglement is a special kind of correlations only found in quantum mechanics. We are all familiar with the concept of correlations. For example, the weather in Southern California is pretty well-correlated from one day to the next—if it is sunny today, it will likely be sunny tomorrow. Quantum systems can be correlated in an even stronger way. Entanglement was first seen as a weird feature of quantum mechanics—Einstein famously referred to it as a "spooky action at a distance." But with the advancement of quantum information science, entanglement is now seen as a physical resource that can be used in information processing, such as in quantum cryptography and quantum computing. One part of my research is to develop methods to characterize and quantify entanglement. Another is to find new applications of entanglement, both in quantum information science and in other areas of physics.
What is a quantum computer?
At the most basic level, computers are made up of millions of simple switches called transistors. Transistors have two states—on or off—which can be represented as the zeroes or ones that make up binary code. With a quantum computer, its basic building blocks (called qubits) can be either a one or a zero, or they can simultaneously exist as a one and a zero. This property is called the superposition principle and, together with entanglement and quantum interference, it is what allows quantum computers to, theoretically, solve certain problems much faster than normal, or "classical," computers could. It will take a long time until we actually have quantum computers, but we are already trying to figure out what they can do.
What is an example of a problem only solvable by a quantum computer?
It is a mathematical fact that any integer number can be factored into the product of prime numbers. For example, 21 can be written as 3 x 7, which are both prime numbers. Factoring a number is pretty straightforward when it is a small number, but factoring a number with a thousand digits would actually take a classical computer billions and billions of years—more time than the age of the universe! However, in 1994 Peter Shor showed that quantum computers would be so powerful that they would be able to factor numbers very quickly. This is important because many current cryptographic systems—the algorithms that protect your credit card information when you make a purchase online, for example—are based on factoring large numbers with the assumption that some codes cannot be cracked for billions of years. Quantum computing would change the way we do cryptography.
What got you interested in quantum information?
During my undergraduate education, I was looking online for interesting things to read, and found some lecture notes about quantum computation which turned out to be by Caltech's John Preskill [Richard P. Feynman Professor of Theoretical Physics]. They are a beautiful set of lecture notes and they were really my first contact with quantum information and, in fact, with quantum mechanics. I have been working in quantum information science ever since. And now that I'm on the Caltech faculty, I have an office right down the hall from Preskill!
What is your background?
I am originally from Brazil. I did my bachelors and masters degrees there in physics, and my PhD at Imperial College London. After that, I moved among London, Brazil, and Switzerland for various postdocs. Then I became faculty at University College London. Last year I was working with the research group at Microsoft, and now I am here at Caltech. The types of problems I have worked on have varied with time, but they are all within quantum information theory. It is stimulating to see how the field has progressed in the past 10 years since I started working on it.
What are you particularly excited about now that you are at Caltech?
I can't think of a better place than Caltech to do quantum information. There are many people working on it from different angles, for example, in the intersection of quantum information and condensed-matter physics, or high-energy physics. I am very excited that I get to collaborate with them.
What do you like to do in your free time?
I used to go traveling a lot, but six months ago my wife and I had a baby, so he is keeping us busy. Along with work and exercise, that basically takes up all my time.


Quantum computers promise to revolutionise the digital world, but how do you tell if a computer really is harnessing the power quantum mechanics? It’s a question that has plagued the only computer manufacturer claiming to produce quantum-powered machines – D-Wave Systems of Burnaby in British Columbia, Canada – since they went on sale.
Today, the publication of further inconclusive tests of the machines is a reminder of just how difficult it is to get an answer. We explain why it’s so hard to test a quantum computer – and whether we’ll ever get an answer to the D-Wave conundrum.
What is quantum computing and why should I care?
Quantum objects can be in multiple states at once, a property known as superposition. This means a quantum bit (qubit), the basic unit of information in computing, can be both a 0 and a 1 at the same time. Theoretically a computer with a large number of these qubits should be able to complete certain tasks, such as factoring numbers or searching large databases, much faster than their ordinary equivalent.
Has anyone built a quantum computer?
Labs around the world have built devices with a handful of working qubits, but they wouldn’t even put a pocket calculator out of business: one of the most impressive results to date is factoring 21 into 3 and 7. Meanwhile, several years ago, D-Wave burst on to the scene, offering up its machines for sale. But despite high-profile customers – including US defence firm Lockheed Martin and Google, which operates its D-Wave machine in partnership with NASA – there are still questions about whether the machines really count as quantum computers. They rely on an alternative theory called adiabatic quantum computing and no one knows whether the theoretical quantum speed-up this provides can be translated to real-world machines.
So is it quantum or not?
D-Wave has demonstrated that its machine behaves in a quantum way and that it can compute things, but the jury is still out on whether it is actually using quantum mechanics to hasten its calculations. “Nobody knows whether it works. It is a totally high-risk, speculative project,” says Matthias Troyer of ETH Zurich in Switzerland. “If it pays off, it is a huge breakthrough.” Earlier this year, Troyer’s team released results from tests of a D-Wave Two machine that suggested there was no quantum speed-up. Today, these results are published in Science (DOI: 10.1126/science.1252319).
Wait, why would anyone buy a computer if they don’t know that it works as claimed?
D-Wave does not publically list the cost of its computers, but they are thought to be $10 to $15 million – a drop in the bucket for a multibillion dollar company like Google. Essentially D-Wave’s customers and investors are hoping to get in on the ground floor of a computing revolution.
Can’t you just test whether it runs faster than a regular computer?
Ye-es, but first you have to figure out what kind of test to run. It has to be a fair fight – one D-Wave-sponsored test that showed apparent gains was later criticised for pitting a specialised quantum algorithm against unoptimised software on an ordinary PC.
What other aspects are necessary for a useful comparison?
The test also has to involve a problem where being quantum actually gives you an advantage. D-Wave computers solve problems in a process similar to exploring a hilly landscape where the lowest points corresponds to the best solution. While an ordinary computer is forced to climb up and over the hills to find the low points, a quantum machine can simply tunnel its way through.
The trouble is that many test problems aren’t challenging enough, leading some to suggest that the reason D-Wave didn’t show a quantum speed-up in some tests – such as Troyer’s – isn’t because it is not able to deliver a better performance, but rather because the test didn’t force it too. “The D-Wave machine would rather use classical resources instead of quantum,” suggests Vadim Smelyanskiy of NASA’s Quantum Artificial Intelligence Laboratory in Mountain View, California, which hosts the Google-purchased computer. D-Wave claims that is the case with Troyer’s test. “Those problems are simply too easy,” says Colin Williams of D-Wave.
Will this one ever be resolved?
Smelyanskiy is currently working with others at NASA and Google to develop tests he hopes will put the machine through its paces, which he presented at the Adiabatic Quantum Computing conference in Los Angeles last week. “You want to construct those tall mountains and absolutely be sure that there is no way around,” he says. “For those problems, we will be able to see if the machine really is forced to do something quantum.”
What happens if the D-Wave machines do strut their quantum stuff?
Even if they do eventually demonstrate a quantum speed-up, they won’t be as good as fully quantum computers, which are still at least 15 to 25 years away, says Smelyanskiy. He says the comparison is similar to the way Charles Babbage’s 19th century analogue difference engine, the precursor to today’s computers, measures up with your current PC. At the moment, D-Wave’s machine is more like a rusty difference engine that doesn’t seem to work properly, but if D-Wave can clean it up, the results could be impressive. “It will probably have the same impact on mankind as the real difference engine had,” he says.
When can I have my own personal quantum computer?
Whatever the future of quantum computers, don’t expect to own one yourself. “This will be a special-purpose device that can solve a limited set of problems much better than a classical one, but it will never be a general purposes machine like your laptop or your iPhone,” says Troyer. “It’s not what we’ll have at home in the future.”
More on these topics:


Scientists Achieve Breakthrough in Polariton Laser Technology
An international scientific team has modeled and conducted an experiment in the course of which they have managed to produce an electrically pumped spin-polarized polariton laser. This allows for a reduction in the laser’s energy consumption levels and control over the output polarization. This is achieved thanks to the use of magnetic materials in the device’s contacts: the electrons that come into contact with the laser have a preferred spin direction, which allows for effective spin pumping. Polariton lasers are very promising for the very reason that they do not require high amounts of energy. In addition, they work at room temperatures. Due to this, they can be used in portable electronics, optical computers and communication devices. Results of the experiment have been published in Physical Review Letters.
The primary advantage of polariton lasers is their low energy consumption. A regular laser is based on the induced radiation effect: if a high-energy excited electron is hit by a photon, the electron “falls” into a low-energy state, producing two photons that are identical to the original one. A cascade of such processes results in the formation of a large number of identical, coherent photons that form the laser emission.
To generate a laser beam, the population inversion condition has to be met: the electron density on the high-energy level must be higher than on the low-energy level. In this way, it is important to “pump into” the system an amount of additional energy that is required to transfer enough electrons onto the high-energy level. The minimum amount of energy required for the formation of laser radiation is referred to as the lasing-action threshold: this value, among other things, determines a laser’s minimum energy requirement.
There is also another process which concerns the type of emission that is called spontaneous: in that case, an electron on the high-energy level can, at a random time, emit a photon and fall into a low-energy state. The issue with spontaneous emission is that the exiting photons tend to be incoherent, with a random phase. This issue can be avoided if all the electrons are put into the same quantum-mechanical state, which would also cause all exiting photons to be identical. Unfortunately, this cannot be done with electrons, as they cannot assume the same quantum-mechanical state according to the so-called Pauli Exclusion Principle, which states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously.
A polariton laser setup. Credit: bibo.kz
In polariton lasers, this limitation is overcome in the following manner: electrons in such systems, by interacting with each other and the light, form composite particles – exciton polaritons. These particles have a full spin, and are thus left unaffected by the Pauli Principle; at low temperatures, they can assume the same quantum-mechanical state. Such a state of matter in which a large fraction of particles occupy the same quantum state is referred to as the Bose-Einstein condensate. If polaritons can disappear from the condensate while spontaneously emitting photons that exit through the cavity face of a laser, the laser output will be coherent just like in a regular laser. Except that the lasing-action threshold does not need be reached any longer! In real life, of course, some amount of energy will still be required, but it will be substantially (by several magnitudes) less than for what is needed for regular, semiconductor-based lasers.
The first polariton lasers have been built in early 00’s; they worked at ultra-low temperatures of several Kelvin and had to be pumped by another laser. In the recent years, both of these issues have been solved: in 2013 an electrically pumped polariton laser that could operate at room temperature was demonstrated. The last remaining issue is that of controlling the polarization of the emission.
“In a polariton laser, two Bose-Einstein condensates tend to form: one with upward-directed spin polaritons, and another with downward-directed ones. Both are emitting independently: as a result, the emitted light’s polarization is linear, and its direction is random. If we could manage to mostly pump one of the condensates, it would allow us to receive a stable, circularly-polarized emission and to also lower the lasing-action threshold, further reducing the laser’s energy consumption. Such spin-selective pumping is quite easy to implement when dealing with optics, but electric spin-polarized pumping has not yet been done,” – comments Ivan Iorsh, one of the article’s authors and an associate professor at ITMO University’s Department of Nanophotonics and Metamaterials.
This is exactly what was accomplished by the international team that also included physicists from the University of Michigan, Nanyang Technological University, University of Southhampton and St. Petersburg State University. The researches have used a ferromagnetic material as a contact in their laser setup, which was used to create a magnetic field. Electrons that entered this system had their spin polarization defined by the ferromagnetic material, which they passed on to the polaritons that formed a condensate. This led to a stable, elliptical polarization of the resulting emission and the lowering of the threshold.
By controlling the spin using a magnetic field, it is also possible to manipulate the light’s polarization. This means that optical signals can be coded through electrical ones. In that case, the direction of polarization would substitute the ones and zeroes – such a setup can be implemented on a microchip with low power consumption that will work at room temperature.
The results of this research were showcased in an experiment at the University of Michigan. The team from ITMO University and St. Petersburg State University modeled the system.
“The experiment has fully confirmed the behavior predicted by our modeling. It’s always amazing to see an experiment confirm a theoretical prediction. The discovered effect is very important for spintronics – the science of coding information not through electrical charges, but through the spin. The main issue there is the inevitable spin relaxation – the loss of spin polarization by electrons due to their interactions with the crystal grating. We have demonstrated the opposite effect – the increase and amplification of spin polarization, which could open up completely new opportunities for application in devices,” – comments Alexey Kavokin, head of the Spin Optics Laboratory at St.Petersburg State University.
He added that another promising area of development in science that is related to polariton lasers is that of quantum simulators based on polariton condensates. Researchers are currently racing to create the first quantum processor. Google’s artificial intelligence laboratory has collected 49 qubits, Mikhail Lukin’s teams at Harvard – 51. The hundred-qubit threshold will likely be crossed in the coming months. Still, the practical application of such systems is highly limited: Google’s superconductor-based processor only works at ultra-low temperatures (less than one degree Kelvin), while Mikhail Lukin’s qubits are based on cold atoms, which can only be kept together in lab conditions.
“In this context, polaritons offer an alternative platform for quantum computations. It is a semiconductor platform, and those are relatively cheap and are easy to integrate into the existing processors. And the main thing that our work with our colleagues from Michigan has shown is that polariton condensates are fine with room temperatures. I’m sure that a semiconductor platform for quantum technology can be created in Russia in a short time. We might even come out ahead of Google!” – adds Kavokin.
The scientist notes that, per his opinion, in the next two or three years polariton lasers will likely see practical application. This is mostly related to their use in the creation of macroscopic multiparticle wave functions at room temperatures. The use of polariton lasers in quantum computing is also a promising venture.
Reference: Room Temperature Spin Polariton Diode Laser, Aniruddha Bhattacharya, Md Zunaid Baten, Ivan Iorsh, Thomas Frost, Alexey Kavokin, Pallab Bhattacharya, 2017, Physical Review Letters.


Often in physics, new discoveries are made by improving the sensitivities of measurements, such as the recent example of the gravitational wave detector. One way to improve the sensitivities for the measurement and transduction of physical forces is cavity optomechanics. Cavity-optomechanics is an interdisciplinary area of mechanical engineering, electrical engineering, optics and quantum physics.It emerged as an independent field of its own only very recently, and utilizes the interaction between mechanical motion and light. Recently featured as the ‘milestone of photon history’ in nature photonics, cavity optomechanics is also one of the chosen fields of interest for Dr. Vibhor Singh, Assistant Professor at the Department of Physics, Indian Institute of Science, Bangalore. Dr. Vibhor has worked extensively in nanomechanical systems during his graduate as well as post doctoral career and has recently joined IISc. He is currently setting up an experimental laboratory to explore various nanomechanical and optomechanical systems.
Cavity optomechanics is about utilizing the interactions between light and motion to control and manipulate their quantum states. Light carries momentum and hence can produce radiation pressure force. Each photon, a particle of light, bouncing off a mirror, for example, imparts some momentum to the mirror. Yet, in our everyday experience, we do not observe mirrors moving when reflecting light. This is because the transferred momentum is small compared to the size of the mirror. However, by increasing the light intensity and using lighter mirrors, the effects of the light radiation can be magnified.
Arrangement of mirrors in a particular way can be used to amplify light by letting the photons from the light source bounce back and forth between the mirrors. In such a system, if one of the mirrors is made extremely light (micrometer thickness or lower) and movable, we obtain an “optomechanical resonator” where the radiation forces of the reflected photons cause mechanical movement of the mirror. A feedback mechanism kicks into action since a change in the mirror position affects the length of the cavity which in turn changes the intensity of light inside it. Thus, the radiation pressure force on the mirror is dependent on its position, leading to a coupling between the optical and mechanical modes. There are several different implementations of such interaction with variations in the size and material of the movable mirror, its placement and the frequency of light used.
So, what are these optomechanical systems good for? As it turns out, there are quite a variety of tricks to be played with this system.
First off is the one involving the infamous Schrödinger’s cat, the popular face of quantum theory. The Schrödinger’s cat refers to the postulate of quantum theory that quantum states can exist in a superposition of various states at the same time. But, such quantum superpositions are observable only in microscopic systems isolated from outside interference since interactions with the environment destroy the superposition. For example, in real life, we do not see a cat being simultaneously dead and alive, like the hypothetical Schrodinger’s cat is capable of. Objects seem to lose their ‘quantumness’ once we are in the macroscopic realm. The mechanism of this decay of quantum states into normal classical states, termed decoherence, is of interest from a fundamental physics point of view. This is where optomechanical resonators step in by presenting us with quantum control over the motion of macroscopic objects (the mirror) via the optical field, thus enabling researchers to prepare superpositions of macroscopic mechanical states. Dr. Vibhor’s lab aims to take advantage of this capability to carry out fundamental tests of quantum theory. These experiments will be carried out at very low temperatures to remove thermal as well as Brownian motion of mechanical systems thus enabling the study of purely quantum mechanical effects.
Dr. Vibhor is also interested in pursuing the potential applications of optomechanical resonators in quantum information technology. Optomechanical resonators act as efficient transducers – devices effecting interconversion between different types of signals – because of the versatility of both the light field and the nanomechanical oscillations to couple to a variety of systems. Such transducers are required in today’s ‘hybrid circuits’ which aim to integrate physical systems such as light and sound along with electronic components in circuits, and specifically find applications in quantum computing.
Quantum computing refers to computing carried out by exploiting quantum mechanical effects.In the hunt for physical systems that can be used as qubits or quantum bits (which are the building blocks of quantum computing just as the two state bits are the basis of classical computing), superconducting circuits have emerged as a worthy competitor. Due to inherent mechanical compliance, optomechanical systems have the potential to act as a transducer to convert quantum information from a superconducting qubit to the optical photons which are good information careers over long distances. Just as optical cables connect the nodes of today’s networks, such interfaces are necessary in connecting the quantum nodes of a future quantum internet.
In charting the future course for his laboratory, Dr. Singh envisions a lab exploring the field of cavity optomechanics from both a fundamental physics as well as an application point of view, especially looking at various implementations in quantum information technology.
About the scientist:
Dr. Vibhor Singh is currently an assistant professor at the Department of Physics, Indian Institute of Science, Bangalore.


In a quantum computer, information is stored not as a string of ones and zeroes, but as a series of quantum-mechanical states: spin directions of electrons, for instance, or polarization orientations of a photon. In 1985 David Deutsch of the University of Oxford pointed out that quantum physical law allows particles to be in more than one state at a time, making it possible for each particle in a quantum computer to hold more than one bit of information. (In this field, the term "bit" is replaced by "qubit," meaning quantum bit.) A computer containing, say, a hundred particles could execute a computation on 2100 numbers at once. The ability to crunch many numbers at the same time--known as massive parallelism--would make quantum computers ideal for some basic computing tasks, such as factoring large numbers. Two years ago, Peter W. Shor of AT&T Bell Labs presented an algorithm showing exactly how a quantum computer would carry out such task.
But there is much more to quantum computers than breaking down large numbers. At last May's ACM Symposium on Theory of Computing, Lov K. Grover, also at Bell Labs, announced a more down-to-earth application: a crafty algorithm that, building on Shor's ideas, would allow a quantum computer to make lightning-fast searches through a database. In this scheme, each item in the database would be represented by a quantum state of a particle in the computer. Relying on the inherently fuzzy laws governing those particles, Grover's algorithm would enhance the state in the system corresponding to the desired item and suppress the others. Rather than slogging dumbly through a list, the algorithm operates on all of the particles at once, so it could far exceed the speed and efficiency of a classical computer.
Such list-searching ability could have applications in many other tasks that require finding the optimal member of a set. And a combined talent for factoring and searching may make quantum computers ideal tools for cracking codes (including the Data Encryption Standard, the official U.S. government cryptographic standard).
Another exciting role for quantum computers involves turning them back on their own world and using them to simulate other quantum-mechanical systems--the behavior of quarks in an atomic nucleus, for instance, or electrons in a superconductor. Seth Lloyd of the Massachusetts Institute of Technology is one of the leading researchers working on concrete ways to realize this exotic idea. In essence, the quantum behavior of one set of particles would act as a proxy for that of a different system, bypassing the extraordinarily complex rules of simulation that normally would need to be programmed into a computer.
While nobody is denying the vast potential of quantum computers, even the most ardent enthusiasts are sobered by the obstacles that must be overcome before usable devices can be built. The greatest of these is that the slightest outside disruption--heat or light, for instance--can destroy the balance of quantum states that stores information and makes the computing possible. In technical terms, the system loses its quantum coherence. The very process of reading the state of a qubit can upset the coherence, so retrieving the result of a calculation poses a tough challenge. Even if the system does not fall apart, quantum computers will naturally tend to accumulate errors; the kinds of error-correction schemes developed for classical computers do not translate to the subatomic realm.
Here too, however, there has been substantial recent progress. Shor is working on a method whereby each piece of information is spread, or entangled, over several qubits. In this way, the erroneous decay of one of the quantum states will not lose the information. Of course, using additional qubits trades off some efficiency. Shor's original scheme involved using nine qubits. More recently, Raymond Laflamme and his colleagues at Los Alamos National Laboratory have derived an error-correction technique that requires only five qubits. Shor is also studying how much error is allowable before it taints the results from quantum computers; in essence, proponents of quantum computing are trying to reinvent from the ground up all of the basic logic problems that other computer scientists have developed since the days of ENIAC, the ancestor of the modern electronic computer.
And the programmers working on ENIAC had a significant advantage over Shor and his ilk: they at least had a physical device to work with. Researchers at the National Institute of Standards and Technology, led by David J. Wineland, and a team headed by H. Jeff Kimble at the California Institute of Technology have made some headway in constructing real quantum systems that function as crude logic gates--sort of nano-transistors. These are only the first baby steps toward a full, workable quantum computer. (Click here to view a schematic of CIT's experimental setup.)
Nevertheless, many people are betting the technical hurdles are manageable. Researchers at M.I.T., Caltech and the University of Southern California have banded together to form the Quantum Information and Computing institute. The Defense Department's Advanced Research Projects Agency (ARPA) is providing a five-year, $5-million grant--a skinny slice of the total defense R&D pie, but a sign of faith that quantum computing will eventually find a place in our macroscopic lives.


Quantum physics—the laws that govern the behavior of smallest components of our universe, such as fundamental particles, atoms and molecules—is admittedly a tough subject, a complicated path of intricate mathematics and scientific theory. Those outside the field who brave the journey often find themselves in a confusing place where the classical principles they learned in school no longer apply and the new rules seem…well…a bit unbelievable. In the quantum world, things can be in two places at once? Better yet, they can be two things at once? What???
If this has been your experience, don’t worry—you’re in very good company. Respected scientists, including Albert Einstein, felt the same way, and made many attempts to prove that these strange new theories couldn’t be correct. Each attempt, however, failed, and instead reinforced the reality of quantum physics in contrast to our conventional intuition. But this is good news—the properties buried in quantum theory hold great promise for exciting, real-world applications.
So how do we make sense of these bizarre new rules? What really makes quantum physics so different, so strange, and so promising? To start, let’s take a look back to 1900 and the work of physicist Max Planck, who first drew back the curtain on the mysterious quantum world.
That year, Planck was embroiled in a nagging physics problem—how to explain the radiation of light emanating from hot objects. At the time, there were two conflicting laws, neither of which was quite right. Sandwiching visible light on the electromagnetic spectrum are infrared waves, which have longer wavelengths and a lower frequency, and ultraviolet waves, which have shorter wavelengths and a higher frequency. One law—Wien’s law—could accurately predict the experimental results of ultraviolet waves, but fell apart when it came to infrared waves. Conversely, the Rayleigh-Jeans law covered infrared waves, but didn’t work for ultraviolet. What Planck needed, then, was one law that would correctly apply to both ends of the spectrum.
For the birth of quantum physics, the details of Planck’s solution to this problem were far less important than the trick he used to arrive at it. This trick, which Planck later on called “happy guesswork,” was simple but unsettling: the radiation energy had to be chopped up into tiny packages, or particles of light. Based on everything physicists knew at the time, this claim was outrageous: light was understood as a wave, which left little space for particles of light, nowadays known as photons. So now light could be…both? While it was not his intent, Planck’s trick was the first step in a chain reaction that turned the physics world upside-down.
We now understand that it’s not just light, but all of the fundamental components of our universe that embrace this dual nature and the other properties of the quantum world. To explain, let’s take another step back, this time to our early science education, and picture electrons—the negatively charged fundamental particles that, together with the positively charged protons and neutral neutrons, make up atoms. Are you picturing them as miniature billiard balls? What about a light wave? Do you imagine it as a tiny version of what comes crashing against the shoreline?
These are convenient pictures, because they are easy to imagine. But what is your evidence that these mental pictures really describe the nature of an electron, and the nature of light? With your sensory perception, you cannot see a single electron, nor observe a light wave oscillate. And, as it turns out, neither light, nor electrons, nor atoms, nor even molecules are simply waves, or just particles.
When it comes to strange quantum properties, this dual wave-particle nature is just the tip of the iceberg. One of the most striking concepts is that of quantum entanglement. It can be illustrated like this: imagine being the proud parent of two children, Susy and Sam, who have just hit the age of disagreeing with each other all the time. They both like mac & cheese as well as pizza. Sadly, this is no longer sufficient to guarantee a drama-free dinner. As a counter strategy, you and your partner team up and question Sam and Susy simultaneously in different rooms. This way, they cannot coordinate their dissent, and you have a 50 percent chance of random agreement on the dinner choice.
Believe it or not, in the quantum world you would be doomed. In an experiment, the two parties could be photons, and the dinner question could be a measurement of their polarization. Polarization corresponds to the direction of oscillation—moving up and down or from side to side—when light behaves as a wave. Even if you separate the two parties, eliminating all communication, quantum physics allows for an invisible link between them known as entanglement. Quantum-Susy might change her answer from day to day (even pizza gets boring after a while), but every single time there is perfect anti-correlation with quantum-Sam’s answer: if one wants pizza, the other opts for mac & cheese—all the time!
This is just one example of the many bizarre properties we know to be true based on careful calculation and experimentation. But if we’re so sure, why do we witness so little of the quantum world?
Much of quantum physics happens at length scales so small that they remain hidden to us, even when using the most powerful microscopes. In addition, witnessing quantum physics at work turns out to be radically different from what you might call an “observation.” Seeing that an object is the color red is a fairly straightforward, unobtrusive process. Probing a quantum object like an electron or photon is an entirely different matter. True quantum behavior tends to be fragile, and attempting to measure it often constitutes a major but unavoidable disruption that usually prevents quantum weirdness from becoming directly visible.
However, just because we cannot see quantum physics in action doesn’t mean that is hasn’t affected our lives in a tangible, positive way. The impact of quantum physics has been enormous: not only is it the prime common factor in nearly all physics Nobel Prizes awarded in the past one-hundred years, but it has also been a crucial driving force in technological advances ranging from lasers and superconductors to medical imaging like MRIs. Indeed, imagining a world in which quantum physics had never been discovered would amount to eliminating a lot of the technology we take for granted each and every day.
The grandest vision, perhaps, is that of harnessing the power of quantum physics for a completely new kind of supercomputer. Such a quantum computer could solve tasks in a heartbeat that would currently require centuries of computation time on the fastest computers available today. Sounds intriguing? Many physicists around the world working on the hardware of such a machine would agree. (To learn more about what would make a quantum computer so powerful, check out the slideshow above.)
They would also explain, however, how daunting the challenges are in this endeavor. Overcoming the fragile nature of quantum behavior is not an easy task—one that rivals the quantum leap of faith taken by Planck and his colleagues to bring us into this new and exciting world.


Two research teams working in the same laboratories at UNSW Australia have found distinct solutions to a critical challenge that has held back the realisation of super powerful quantum computers.
The teams created two types of quantum bits, or "qubits" – the building blocks for quantum computers – that each process quantum data with an accuracy above 99%. The two findings have been published simultaneously today in the journal Nature Nanotechnology.
"For quantum computing to become a reality we need to operate the bits with very low error rates," says Scientia Professor Andrew Dzurak, who is Director of the Australian National Fabrication Facility at UNSW, where the devices were made.
"We've now come up with two parallel pathways for building a quantum computer in silicon, each of which shows this super accuracy," adds Associate Professor Andrea Morello from UNSW's School of Electrical Engineering and Telecommunications.
The UNSW teams, which are also affiliated with the ARC Centre of Excellence for Quantum Computation & Communication Technology, were first in the world to demonstrate single-atom spin qubits in silicon, reported in Nature in 2012 and 2013.
Now the team led by Dzurak has discovered a way to create an "artificial atom" qubit with a device remarkably similar to the silicon transistors used in consumer electronics, known as MOSFETs. Post-doctoral researcher Menno Veldhorst, lead author on the paper reporting the artificial atom qubit, says, "It is really amazing that we can make such an accurate qubit using pretty much the same devices as we have in our laptops and phones".
Meanwhile, Morello's team has been pushing the "natural" phosphorus atom qubit to the extremes of performance. Dr Juha Muhonen, a post-doctoral researcher and lead author on the natural atom qubit paper, notes: "The phosphorus atom contains in fact two qubits: the electron, and the nucleus. With the nucleus in particular, we have achieved accuracy close to 99.99%. That means only one error for every 10,000 quantum operations."
Dzurak explains that, "even though methods to correct errors do exist, their effectiveness is only guaranteed if the errors occur less than 1% of the time. Our experiments are among the first in solid-state, and the first-ever in silicon, to fulfill this requirement."
The high-accuracy operations for both natural and artificial atom qubits is achieved by placing each inside a thin layer of specially purified silicon, containing only the silicon-28 isotope. This isotope is perfectly non-magnetic and, unlike those in naturally occurring silicon, does not disturb the quantum bit. The purified silicon was provided through collaboration with Professor Kohei Itoh from Keio University in Japan.
The next step for the researchers is to build pairs of highly accurate quantum bits. Large quantum computers are expected to consist of many thousands or millions of qubits and may integrate both natural and artificial atoms.
Morello's research team also established a world-record "coherence time" for a single quantum bit held in solid state. "Coherence time is a measure of how long you can preserve quantum information before it's lost," Morello says. The longer the coherence time, the easier it becomes to perform long sequences of operations, and therefore more complex calculations.
The team was able to store quantum information in a phosphorus nucleus for more than 30 seconds. "Half a minute is an eternity in the quantum world. Preserving a 'quantum superposition' for such a long time, and inside what is basically a modified version of a normal transistor, is something that almost nobody believed possible until today," Morello says.
"For our two groups to simultaneously obtain these dramatic results with two quite different systems is very special, in particular because we are really great mates," adds Dzurak.
Associate Professor Morello and Scientia Professor Dzurak are at the School of Electrical Engineering & Telecommunications, UNSW Australia. They are team leaders at the ARC Centre of Excellence for Quantum Computation and Communication Technology, headquartered at UNSW. The quantum bit devices were constructed at UNSW at the Australian National Fabrication Facility, with support from researchers at the University of Melbourne and the Australian National University. The research was funded by: the Australian Research Council, the US Army Research Office, the NSW Government, UNSW Australia and the University of Melbourne.
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Researchers at the University of Michigan's Center for Optical Coherent and Ultrafast Science (FOCUS) and Department of Physics have reported the first demonstration of laser-cooling of individual trapped atoms of different species.
This may be an important step in the construction of a future "quantum computer," in which quantum superpositions of inputs are processed simultaneously in a single device. Trapped atoms offer one of the only realistic approaches to precisely controlling the complex quantum systems underlying a quantum computer.
The demonstration is described in the April 2002 issue of Physical Review in an article, "Sympathetic Cooling of Trapped Cd+ Isotopes," by Boris B. Blinov, Louis Deslauriers, Patricia Lee, Martin J. Madsen, Russ Miller, and Christopher Monroe.
Partially based on these results, Monroe has proposed a new "Architecture for a Large-Scale Ion-Trap Quantum Computer," with co-authors David Kielpinski (MIT) and David Wineland (National Institute of Standards and Technology), in the June 13 issue of the journal Nature.
Interest in quantum computing has mushroomed in the last decade as its potential for efficiently solving difficult computing tasks, like factoring large numbers and searching large databases, has become evident. Encryption and its obverse, codebreaking, are just two of the applications envisioned for quantum computing if and when it becomes a practical technology.
Quantum computation has captured the imagination of the scientific community, recasting some of the most puzzling aspects of quantum physics---once pondered by Einstein, Schroedinger and others---in the context of advancing computer science. "Right now, there's a lot of black magic involved in understanding what makes a quantum computer tick and how to actually build one," Monroe said.
"Many physicists doubt we'll ever be able to do it, but I'm an optimist. We may not get there for decades, but given enough time and resources---and failing unexpected roadblocks like the failure of quantum mechanics---we should be able to design and build a useable quantum computer. It's a risky business, but the potential payoff is huge."
In their experiment, the Michigan researchers used electric fields to confine a crystal of exactly two Cd+ atoms of different isotopes. They were able to cool the single 112Cd+ atom to a chilly 0.001 degree Celsius above absolute zero through direct laser cooling of the neighboring 114Cd+ atom. Laser cooling of this "refrigerator atom" removes unwanted motion in the atom crystal without affecting the internal state of the other atom.
This is an important step toward scaling a trapped atom computer, where "qubits" of information are stored in the quantum states within the individual atoms.
The architecture proposed in the Nature article describes a "quantum charge-coupled device" (QCCD) consisting of a large number of interconnected atom traps. A combination of radiofrequency (RF) and quasistatic electric fields can be used to change the operating voltages of these traps, confining a few charged atoms in each trap or shuttling them from trap to trap, and the traps can be combined to form complex structures. The cooling of multiple species demonstrated at Michigan is a key component of this broader proposal.
"This is a realistic architecture for quantum computation that is scalable to large numbers of qubits," the authors conclude. "In contrast to other proposals, all quantum state manipulations necessary for our scheme have already been experimentally tested with small numbers of atoms, and the scaling up to large numbers of qubits looks straightforward."
Frontiers in Optical Coherent and Ultrafast Science
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Bell Labs Scientists Usher in New Era of Molecular-Scale Electronics
Murray Hills - Oct 17, 2001
Scientists from Lucent Technologies' Bell Labs have created organic transistors with a single-molecule channel length, setting the stage for a new class of high-speed, inexpensive carbon-based electronics.
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There are many different schemes for making quantum computers work (most of them evil). But they pretty much all fall into two categories. In most labs, researchers work on what could be called a digital quantum computer, which has the quantum equivalent of logic gates, and qubits are based on well-defined and well-understood quantum states. The other camp works on analog devices called adiabatic quantum computers. In these devices, qubits do not perform discrete operations, but continuously evolve from some easily understood initial state to a final state that provides the answer to some problem. In general, the analog and digital camps don't really mix. Until now, that is.
The adiabatic computer is simpler than a quantum computer in many ways, and it is easier to scale. But an adiabatic computer can only be generalized to any type of problem if every qubit is connected to every other qubit. This kind of connectivity is usually impractical, so most people build quantum annealers with reduced connectivity. These are not universal and cannot, even in principle, compute solutions to all problems that might be thrown at it.
The issues with adiabatic quantum computers don't end there. Adiabatic quantum computers are inherently analog devices: each qubit is driven by how strongly it is coupled to every other qubit. Computation is performed by continuously adjusting these couplings between some starting and final value. Tiny errors in the coupling—due to environmental effects, for instance—tend to build up and throw off the final value.
For annealers with limited connectivity—each qubit is only connected to a few other qubits, rather than all other qubits—this is not such an issue. The coupling between these qubits tends to be strong, so the noise is small compared to the coupling. For a fully interconnected adiabatic quantum computer, however, the weak connections between distant qubits are very sensitive to environmental noise. Thus, errors accumulate—if you are unlucky, pi ends up equal to three.
Digital quantum computing, which uses logic operations and quantum gates, offers the possibility of error correction. By encoding information in multiple qubits, you can detect and correct errors. Unfortunately, digital qubits are delicate things compared to those used in adiabatic quantum computers, and the ability to program and run complex problems with them is out of reach at the moment.
What if the computation was performed by qubits that were operating as an adiabatic quantum computer, but with connections between the qubits controlled via a digital network of qubits?
What about a hybrid approach? That's the question asked by a international group of researchers in a recently-published paper in Nature. They’ve tested a system where the computation is performed by qubits that were operating as an adiabatic quantum computer, but with connections between the adiabatic qubits is controlled via a digital network of qubits. This allows the benefits of scale and flexibility that you get from adiabatic quantum computing, while also making the connections less susceptible to noise.
Digital vs. analog
Let me make an analogy here. Imagine that I have an instrument that measures the hot air concentration in Congress (dangerously high when in session). The instrument produces an analog voltage that is displayed on an analog meter right at the instrument, and the results are relayed to a second analog meter in my home in the Netherlands. The meter in Washington shows a reasonably accurate value with a strong correlation between the reading of hot air displayed in the Capitol Building and speeches by members of Congress. But the distance to my house is so great that my needle only shows an awful lot of noise.
So, instead of transporting the signal directly, I digitize it, encode it, and send it via a network to my home, where it is re-converted to an analog signal and read by my meter. Now, my meter is almost as accurate as the local meter. The only differences between the two are the errors due to the two conversions between digital and analog domains.
In other words, as long as the process that converts between digital and analog domains generates less noise than the transport of the analog signal, you win. And that is exactly the determining factor for a hybrid adiabatic quantum computer as well. The difference is that, instead of measuring methane concentrations, we are varying the coupling between qubits. Instead of a continuous, slow change, the coupling is stepped from value to value in jumps that are determined by the number of qubits in the digital part of the circuit.
Now, as you might have guessed, this is very expensive in terms of quantum gates. With the new hardware, the researches have an adiabatic quantum computer with up to nine computational qubits. In the interests of reproducibility, I can say that the digital connection between two qubits involves... wait for it... hmm, well, the researchers don't say how they are connected to each other.
In fact, the whole paper in Nature seems to lack details on how this quantum computer is laid out. All we get is one tiny electron microscope picture of nine qubits in a row, with none of the coupling network shown. But, we get some idea of how the hardware works from various things that the researchers say when describing it.
For a four qubit case, the link between each qubit seems to require a cluster of 48 qubits for control. The link itself is made up of five entangled qubits, coming to a grand total of 159 qubits. The authors also mention that for nine computation qubits, they need about 1,000 auxiliary qubits for control purposes. Yet despite all of the supporting digital architecture, there are still only 5 steps between the start and end of the computation.
The big question is, of course, does it work? And you know that it must have, because otherwise it, and the researchers that worked on it, would be gathering dust in a cupboard somewhere. The researchers were able to compare their implementation to a model of an ideal version and to a noise-free analog model. Now, since the digitization was very coarse, the answers to the toy problems that they got the computer to solve are not terribly accurate compared to the analog case. But they do show that their real digital version performs about as well as can be expected. That is, the model of the digitized adiabatic quantum computer and the real digitized adiabatic quantum computer performed about the same.
That is faint praise, though. My impression is that this is a huge engineering feat. The researchers have implemented not just a multi-qubit adiabatic quantum computer, but also a complex quantum digital network between the qubits. To give you an idea of the complexity: each qubit in the network is, even when you don't want it to, able to talk to the rest of the network. So, setting the coupling between any two qubits varies the coupling of adjacent qubits too.
To prevent this, the researchers developed an impressive set of decoupling sequences. Instead of actually stating what this means, let me use an analogy. Imagine that you and some friends are in a row of rooms that are joined by a set of vertical windows. If two of you are standing up, you can communicate using hand signs; if you are both lying down, you can communicate with hand signs. But, if one of you is lying down and the other is standing up, you cannot see each other's hands and no communication is possible. And, if people are in the rooms in between, they might block your view anyway.
So, for you to communicate with one of your friends, you have to do two things: you have to make sure you and your friend have the same orientation. And, since the rooms are all in a row, you have to make sure that all the people in between you are in the opposite orientation.
When I started writing about quantum computing, it was lab stuff... Now, things are starting to get scary.
This is pretty much what decoupling sequences do: they change the state of a qubit so that the coupling between it and the qubit you want to manipulate is at a minimum (ideally, zero, but in practice it is never quite zero). After you've performed the desired operation on the target qubit, you reverse the decoupling operation to return the qubit to its original state. This requires exquisite control and timing to get right. And, in this paper, that sort of control was impressively demonstrated on a large scale.
When I started writing about quantum computing, it was lab stuff of mostly academic interest. We celebrated every qubit and every time there was evidence of quantum goodness in our computing. Now, things are starting to get scary. Computations involving many qubits are common. And companies—not just startups, but serious companies that do serious things like setting milestones—are getting involved.
There is still a long way to go before a useful quantum computer emerges. But in the past there were also an awful lot of "if" statements associated with every "when" statement. Those qualifiers are being worked through very quickly, and the "when" is looking a good deal more certain.
Nature, 2016: DOI: 10.1038/nature17658


Over 400 million transistors are packed on dual-core chips manufactured using Intel's 45nm process. That'll double soon, per Moore's Law. And it'll still be like computing with pebbles compared to quantum computing.
Quantum computing is a pretty complicated subject—uh, hello, quantum mechanics plus computers. I'm gonna keep it kinda basic, but recent breakthroughs like this one prove that you should definitely start paying attention to it. Some day, in the future, quantum computing will be cracking codes, powering web searches, and maybe, just maybe, lighting up our Star Trek-style holodecks.
Before we get to the quantum part, let's start with just "computing." It's about bits. They're the basic building block of computing information. They've got two states—0 or 1, on or off, true or false, you get the idea. But two defined states is key. When you add a bunch of bits together, usually 8 of 'em, you get a byte. As in kilobytes, megabytes, gigabytes and so on. Your digital photos, music, documents, they're all just long strings of 1s and 0s, segmented into 8-digit strands. Because of that binary setup, a classical computer operates by a certain kind of logic that makes it good at some kinds of computing—the general stuff you do everyday—but not so great at others, like finding ginormous prime factors (those things from math class), which are a big part of cracking codes.
Quantum computing operates by a different kind of logic—it actually uses the rules of quantum mechanics to compute. Quantum bits, called qubits, are different from regular bits, because they don't just have two states. They can have multiple states, superpositions—they can be 0 or 1 or 0-1 or 0+1 or 0 and 1, all at the same time. It's a lot deeper than a regular old bit. A qubit's ability to exist in multiple states—the combo of all those being a superposition—opens up a big freakin' door of possibility for computational powah, because it can factor numbers at much more insanely fast speeds than standard computers.
Entanglement—a quantum state that's all about tight correlations between systems—is the key to that. It's a pretty hard thing to describe, so I asked for some help from Boris Blinov, a professor at the University of Washington's Trapped Ion Quantum Computing Group. He turned to a take on Schrödinger's cat to explain it: Basically, if you have a cat in a closed box, and poisonous gas is released. The cat is either dead, 0, or alive, 1. Until I open the box to find out, it exists in both states—a superposition. That superposition is destroyed when I measure it. But suppose I have two cats in two boxes that are correlated, and you go through the same thing. If I open one box and the cat's alive, it means the other cat is too, even if I never open the box. It's a quantum phenomenon that's a stronger correlation than you can get in classical physics, and because of that you can do something like this with quantum algorithms—change one part of the system, and the rest of it will respond accordingly, without changing the rest of the operation. That's part of the reason it's faster at certain kinds of calculations.
The other, explains Blinov, is that you can achieve true parallelism in computing—actually process a lot of information in parallel, "not like Windows" or even other types of classic computers that profess parallelism.
So what's that good for? For example, a password that might take years to crack via brute force using today's computers could take mere seconds with a quantum computer, so there's plenty of crazy stuff that Uncle Sam might want to put it to use for in cryptography. And it might be useful to search engineers at Google, Microsoft and other companies, since you can search and index databases much, much faster. And let's not forget scientific applications—no surprise, classic computers really suck at modeling quantum mechanics. The National Institute of Science and Technology's Jonathan Home suggests that given the way cloud computing is going, if you need an insane calculation performed, you might rent time and farm it out to a quantum mainframe in Google's backyard.
The reason we're not all blasting on quantum computers now is that this quantum mojo is, at the moment, extremely fragile. And it always will be, since quantum states aren't exactly robust. We're talking about working with ions here—rather than electrons—and if you think heat is a problem with processors today, you've got no idea. In the breakthrough by Home's team at NIST—completing a full set of quantum "transport" operations, moving information from one area of the "computer" to another—they worked with a single pair of atoms, using lasers to manipulate the states of beryllium ions, storing the data and performing an operation, before transferring that information to a different location in the processor. What allowed it to work, without busting up the party and losing all the data through heat, were magnesium ions cooling the beryllium ions as they were being manipulated. And those lasers can only do so much. If you want to manipulate more ions, you have to add more lasers.
Hell, quantum computing is so fragile and unwieldy that when we talked to Home, he said much of the effort goes into methods of correcting errors. In five years, he says, we'll likely be working with a mere tens of qubits. The stage it's at right now, says Blinov, is "the equivalent of building a reliable transistor" back in the day. But that's not to say those of tens of qubits won't be useful. While they won't be cracking stuff for the NSA—you'll need about 10,000 qubits for cracking high-level cryptography—that's still enough quantum computing power to calculate properties for new materials that are hard to model with a classic computer. In other words, materials scientists could be developing the case for the iPhone 10G or the building blocks for your next run-of-the-mill Intel processor using quantum computers in the next decade. Just don't expect a quantum computer on your desk in the next 10 years.
Special thanks to National Institute of Standards and Technology's Jonathan Home and the University of Washington Professor Boris Blinov!
Still something you wanna know? Send questions about quantum computing, quantum leaps or undead cats to email@example.com, with "Giz Explains" in the subject line.


Quantum internet and hybrid quantum computers, built out of subsystems that operate by means of various physical phenomena, are now becoming more than just the stuff of imagination. In an article just published in the journal Nature Photonics, physicists from the University of Warsaw’s Faculty of Physics (FUW) and the University of Oxford have unveiled a key element of such systems: an electro-optical device that enables the properties of individual photons to be modified. Unlike existing laboratory constructions, this new device works with previously unattainable efficiency and is at the same time stable, reliable, and compact.
Building an efficient device for modifying the quantum state of individual photons was an exceptionally challenging task, given the fundamental differences between classical and quantum computing.
Contemporary computing systems are based on the processing of groups of bits, each of which is in a specific, well-known state: either 0 or 1. Groups of such bits are continually being transferred both between different subcomponents within a single computer, and between different computers on the network. We can illustrate this figuratively by imagining a situation in which trays of coins are being moved from place to place, with each coin laying either with the heads side or the tails side facing upwards.
Things are more complicated in quantum computing, which relies on the phenomenon of superposition of states. A quantum bit, known as a qubit, can be both in the 1 state and the 0 state at the same time. To continue the analogy described above, this would be like a situation in which each coin is spinning on its edge. Information processing can be described as “quantum” processing as long as this superposition of states can be retained during all operations — in other words, as long as none of the coins gets tipped out of the spinning state while the tray is being moved.
“In recent years, physicists have figured out how to generate light pulses with a specific wavelength or polarization, consisting of a single quantum — or excitation — of the electromagnetic field. And so today we know how to generate precisely whatever kind of quantum ‘spinning coins’ we want,” says Dr. Michal Karpinski from the Institute of Experimental Physics (FUW), one of the authors of the publication. “But achieving one thing always leaves you wanting more! If we now have individual light quanta with specific properties, it would be useful to modify those properties. The task is therefore more or less this: take a spinning silver coin and move it from one place to another, but along the way quickly and precisely turn it into a gold coin, naturally without tipping it over. You can easily see that the problem is nontrivial.”
Existing methods of modifying individual photons have utilized nonlinear optical techniques, in practice attempting to force an individual photon to interact with a very strong optical pump beam. Whether the photon so subjected actually gets modified is a matter of pure chance. Moreover, the scattering of the pump beam may contaminate the stream of individual photons. In constructing the new device, the group from the University of Warsaw and the University of Oxford decided to make use of a different physical phenomenon: the electro-optic effect occurring in certain crystals. It provides a way to alter the index of refraction for light in the crystal — by varying the intensity of an external magnetic force that is applied to it (in other words, without introducing any additional photons!).
“It is quite astounding that in order to modify the quantum properties of individual photons, we can successfully apply techniques very similar to those used in standard fiber-optic telecommunications,” Dr. Karpinski says.
Using the new device, the researchers managed — without disrupting the quantum superposition! — to achieve a six-fold lengthening of the duration of a single-photon pulse, which automatically means a narrowing of its spectrum. What is particularly important is that the whole operation was carried out while preserving very high conversion efficiency. Existing converters have operated only under laboratory conditions and were only able to modify one in several tens of photons. The new device works with efficiency in excess of 30%, up to even 200 times better than certain existing solutions, while retaining a low level of noise.
“In essence we process every photon entering the crystal. The efficiency is less than 100% not because of the physics of the phenomenon, but on account of hard-to-avoid losses of a purely technical nature, appearing for instance when light enters of exits optical fibers,” explains PhD student Michal Jachura (FUW).
The new converter is not only efficient and low-noise, but also stable and compact: the device can be contained in a box with dimension not much larger than 10 cm (4 in.), easy to install in an optical fiber system channeling individual photons. Such a device enables us to think realistically about building, for instance, a hybrid quantum computer, the individual subcomponents of which would process information a quantum way using different physical platforms and phenomena. At present, attempts are being made to build quantum computers using, among others, trapped ions, electron spins in diamond, quantum dots, superconducting electric circuits, and atomic clouds. Each such system interacts with light of different properties, which in practice rules out optical transmission of quantum information between different systems. The new converter, on the other hand, can efficiently transform single-photon pulses of light compatible with one system into pulses compatible with another. Scientists are therefore gaining at a real pathway to building quantum networks, both small ones within a single quantum computer (or subcomponent thereof), and global ones providing a way to send data completely securely between quantum computers situated in different parts of the world.