As the amount of data in the world is rapidly increasing, so is the time required for machines to process it. Augmented Reality, Virtual Reality, Artificial Intelligence, Robotics, Real-Time Analytics, and Machine Learning algorithms are needing the cloud to be infinitely faster as well as to require unlimited computing power and an endless amount of storage. Interestingly, this is happening on heels of the slow down of Moore’s law. Chip maker Intel has signaled a slowing of Moore’s Law, a technological phenomenon that has played a role in almost every significant advancement in engineering and technology for decades. We are no longer able to cram transistors in the circuits at the velocity we have been doing.
By 2025, the needs for traditional compute functionality in the cloud will be so large that it can never be built.
Quantum computing’s arrival promises to revolutionize the cloud. What quantum computing provides is massively parallel processing, atomic-level storage, and security using the laws of physics rather than external cryptographic methods. If you have not begun looking at it, the time is now. The cloud will soon be powered by quantum computing, and software will be written in another way.
IBM, Microsoft, Google, Intel, D-Wave have made tremendous advances this year. It is now here to push the bounds of computer performance further forward.
What is Quantum Computing?
Quantum computing is about making use of quantum states of subatomic particles to perform memory and processing tasks. Classical computers switch transistors encode information as bits which represent either a ONE or a ZERO. In contrast, quantum computers use the fundamental building blocks of atoms (such as electrons, protons, and photons) themselves. These subatomic particles spin, so if the spin is in one direction — up, for example — that could be the equivalent of the ONE in a conventional computer, while a particle with a down spin could be a ZERO.
As per the laws of quantum physics, it may not be clear whether a particle has an up or a down spin. Or, perhaps something in between. These subatomic particles possess all of those properties all at the same time. This is called superposition. ONE qubit (a new term to refer to a quantum bit unlike classical bit) can exist simultaneously as a ZERO or a ONE. Two qubits can exist simultaneously as the four possible two-bit numbers (00, 01, 10, and 11). These superpositions allow qubits to perform multiple calculations at once rather than in sequence like a traditional machine. For example, you can compute four calculations with two qubits.
What quantum computing gives you is massively parallel processing!
An understandable example is Grover Search Algorithm. Think about a game where an prize is hidden behind one of four doors and you have to find the prize while opening as few doors as possible. A traditional computer will need to do, on average, a little over two operations to find the prize as it has to open each door in succession. The quantum computer, however, can locate the prize with one action because it can open all four doors at once! You can perform eight calculations with the three qubits. The number of such computations double for each additional qubit, leading to an exponential speed-up. A quantum computer comprised of 500 qubits would have a potential to do 2^500 calculations (much larger than the Shannon Number) in one operation.
Top five things you should know about it
- We will write programs differently. New programming paradigms and languages, new algorithms, as well as a new way of writing logic!
- Quantum computer is “thousands of times” faster than a conventional computer. Google announced it has a Quantum computer that is 100 million times faster than any classical computer in its lab.
- Quantum computing revolutionizes the way that we approach machine learning and artificial intelligence. It will accelerate machine learning remarkably. Quantum computers will reduce power consumption anywhere from 100 to 1000 times because quantum computers use quantum tunneling.
- Quantum computing will destroy the internet security as it is known today. It would be able to crack several of today’s encryption techniques such as RSA and ECC within days if not hours. In this regards, Quantum computing is like a deja vu of discovering the use of enormous energy locked in an atom. Nuclear fission was found in 1938, nine months before the beginning of the Second World War, and it changed the world. Quantum computing could be the IT equivalent of an Atomic Bomb. We are now in a race against time to prepare modern cryptographic techniques before they get broken. New security methods that will allow us to secure data using the laws of physics rather than using external cryptographic methods.
- Quantum computing is not for every problem. Classical computers are still better than Quantum computers at some tasks such as spreadsheets or desktop publishing. However, Quantum computing will be incredibly useful for solving notable chemistry issues, self driving cars coordination, financial modeling, weather forecasting, and particle physics, etc.Have you written your first quantum program yet? In the next few articles, I will go over how how to program using Quantum computing, how to determine which problems are best to be addressed between Quantum computing vs. Classical computing, how it impacts Machine Learning, and how you will develop killer apps such as self-driving car coordination as well as the challenges/solutions in the world where cryptography and quantum computing intersect. Quantum computing revolutionizes the way we approach computer science and logic. A lot of algorithms will need to be redesigned/rewritten using quantum computing paradigms – looking forward to it!PS: Isn’t this a remarkable pic? The heading picture is from the October 1927 Fifth Solvay International Conference on Electrons and Photons, where the world’s most notable physicists met to discuss the newly formulated quantum theory. Seventeen of the 29 attendees were or became Nobel Prize winners!


(Source: Ozz Design/Shutterstock.com)
Quantum technologies are an area, once manifested, that could change the face of many technology-based applications. Although quantum technologies are not quite there yet, scientists have already managed to create devices that can transmit data using quantum networks, albeit for a matter of nanoseconds at low temperatures. Nevertheless, gains are being made—with semiconductors currently leading the way as the fundamental building blocks—and if you look at the huge advances made in classical computing technologies over the past few decades, then quantum technologies might not be as far away as many think.
Quantum technology will be valuable for many reasons, especially for anything that uses a computer chip, as it will enable more operations to be performed simultaneously—and at a greater speed than modern-day computers—while providing an extra layer of encryption that is much needed in today’s online world.
Behind any quantum technology is the quantum bit—otherwise known as a qubit—and is similar, yet so very different, to a classic computing bit. Qubits are the building blocks of quantum networks, much like classical bits are in classical networks. Classical computing bits—known to many as binary bits– can take one of two forms. These are a 1 and 0. Qubits can also take the form of a 1 or 0, but there is a third form that is not possible with classical bits, and that is a superimposable form that can take the form of either a 1 or a 0. Because the superimposable form can take either form, operations can be performed in both values simultaneously—something not possible with classical networks. It is one of the fundamental reasons why quantum networks will be able to process multiple operations at much higher speeds than classical networks.
Figure 1: Qubits, the building blocks of quantum networks, can come in three forms and possess infinite value. (Source: Production Perig/Shutterstock.com)
Each qubit can possess an infinite value within each of the three forms. This leads to a continuum of states where each qubit becomes one and indistinguishable from each other. Although the individual qubit uses the spin of electrons and polarization of photons to store data, they can become entangled, which makes them act as a unified system. This means that each quantum network is described and used as a complete system, rather than a series of qubits.
Quantum entanglement is an important phenomenon in quantum networks. Electrons, photons, atoms, and molecules can all become entangled in these networks. The entanglement within a quantum network also extends over long distances. When one part of the quantum network is measured, the properties of the corresponding entangled qubit(s) within that specific network can be deduced as a definitive value. This enables many networks to be built up, all of which have different values and properties, but where all the qubits in a single network share the same information.
Quantum teleportation is another phenomenon that enables quantum technologies to function, and is similar in nature to quantum entanglement. Quantum teleportation is the process where the data and/or information held in the qubit—which is held there by the electrons spinning up or down, and by polarizing the photons in a vertical or horizontal orientation—is transported from one location to another without transporting the qubit itself.
Most qubits become entangled in these networks; however, if doubt exists that they haven’t become entangled, they can be tested using coincidence correlation. Coincidence correlation assumes that an entangled network can only emit one photon at a time. You can use multiple photodetectors to see how many photons are emitted by a single network. If more than one photon is recorded at any one time, then you can assume that the quantum network is not a single-photon system, and therefore not entangled.
The materials that make up the qubits are an essential part of establishing a quantum network. The quantum system is formed by manipulating physical materials, so the properties and characteristics of the materials used to build a quantum network is a major consideration. For any material to be considered as the building block of a quantum technology, it needs to possess long-lived spin states, which it can control, and be able to operate parallel qubit networks.
Many physical parts also go into designing a quantum network. One of the key features the quantum system requires is an arrangement of interconnected communication lines between each network. Just like in classical computing, these communication lines run between end nodes. These nodes are representative of the information held within an individual quantum network, and this becomes more important for larger and/or complex quantum networks where a lot of different types of information are held within the quantum system. These end nodes can take many forms, although the most popular choices at the moment are:
Two other physical components are crucial if a quantum network is to function as it should. These are the communication lines and quantum repeaters. The physical communication lines currently take two main forms, which are fiber-optic networks and free-space networks, and both work differently. Physical communication lines made from fiber-optic cables send a single photon by attenuating a telecommunication laser, and the path of the photon is controlled by a series of interferometers and beam splitters before it is detected and received by a photodetector. Free-space networks, on the other hand, rely on the line of sight between both ends of the communication pathway. As it stands, both can be used over long distances, but free-space networks suffer from less interference, have higher transmission rates, and are faster than fiber-optic networks.
The other important component is the repeater, which ensures that the quantum network does not lose its signal or become compromised because of decoherence—which is the loss of information due to environmental noise. It is a straight-forward process in classical networks, because an amplifier simply boosts the signal. For quantum networks, it is much trickier. Quantum networks need to employ a series of trusted repeaters, quantum repeaters, error correctors, and entanglement purifying mechanisms to test the infrastructure, to keep the qubits entangled, to detect any short-range communication errors, and to minimize the degree of decoherence in the network.
An extra layer of security can be incorporated into quantum networks through quantum key distribution, which utilizes the principles of quantum mechanics to perform cryptographic operations. This will be a particularly useful tool for when two people are communicating via a quantum network, or data is being transmitted from location to another. The encryption process will utilize randomly polarized photons to transmit a random number sequence. These sequences then act as keys in the cryptographic system. The theory behind these cryptographic systems is that they will use two networks—a classical channel and a quantum channel—between two different communication points, where both channels play specific roles. The classical channel is there to perform classical operations and is a way of seeing if anyone is trying to hack into the network. However, the qubits containing the data will be sent over the quantum channel, which means that the classical system can be hacked, but the hackers will not obtain any information—as no information would exist in that channel. The way that these systems will be able to tell if a network has been hacked is down to the correlation of the signal. Classical networks are highly correlated, and if any imperfections occur between the source and the receiver in the channel, then the system will know if a hack has been attempted.
Although the realization of quantum technologies in everyday systems might be a while off yet, the potential is there for these technologies to revolutionize the computing and communication spaces. The ability for quantum networks to become one and be transmitted over long distances has many advantages over classical systems, which include the potential for faster data transmission types, the ability to perform multiple operations simultaneously, and for highly encrypted data communication channels.
Liam Critchley is a writer, journalist and communicator who specializes in chemistry and nanotechnology and how fundamental principles at the molecular level can be applied to many different application areas. Liam is perhaps best known for his informative approach and explaining complex scientific topics to both scientists and non-scientists. Liam has over 350 articles published across various scientific areas and industries that crossover with both chemistry and nanotechnology.
Liam is Senior Science Communications Officer at the Nanotechnology Industries Association (NIA) in Europe and has spent the past few years writing for companies, associations and media websites around the globe. Before becoming a writer, Liam completed master’s degrees in chemistry with nanotechnology and chemical engineering.
Aside from writing, Liam is also an advisory board member for the National Graphene Association (NGA) in the U.S., the global organization Nanotechnology World Network (NWN), and a Board of Trustees member for GlamSci–A UK-based science Charity. Liam is also a member of the British Society for Nanomedicine (BSNM) and the International Association of Advanced Materials (IAAM), as well as a peer-reviewer for multiple academic journals.
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Nobody has built a quantum computer much more powerful than a pocket calculator but that hasn’t stopped people worrying about the implications of the post-quantum computing world. Most worried are the people who rely on cryptographic codes to protect sensitive information. When the first decent-sized quantum computer is switched on, previously secure codes such as the commonly used RSA algorithm will become instantly breakable.
Which is why cryptographers are scurrying about looking for codes that will be secure in the post-quantum world. Today, Hang Dinh at the University of Connecticut and a couple of pals show that cryptographers have been staring at one all along. They say that a little-used code developed by the CalTech mathematician Robert McEliece in 1978 can resist all known attacks by quantum computers.
First, let’s a make a distinction between symmetric and asymmetric codes. Symmetric codes use identical keys for encrypting and decrypting a message. Quantum computers can dramatically speed up an attack against these kinds of codes. However, symmetric codes have some protection. Doubling the size of the key counteracts this speed up. So it is possible for code makers to stay ahead of the breakers, at least in theory. (Although in practice, the safe money would be on the predator in this cat and mouse game. )
Asymmetric codes use different keys for encrypting and decrypting messages. In so-called public key encryption systems such as the popular RSA algorithm, a public key is available to anyone who can use it to encrypt a message. But only those with a private key can decrypt the messages and this, of course, is kept secret.
The security of these systems relies on so-called trap door functions: mathematical steps that are easy to make in one direction but hard to do in the other. The most famous example is multiplication. It is easy to multiply two numbers together to get a third but hard to start with the third number and work out which two generated it, a process called factorisation.
But in 1994, the mathematician Peter Shor dreamt up a quantum algorithm that could factorise much faster than any classical counterpart. Such an algorithm running on a decent quantum computer could break all known public key encryption systems like a 4-year old running amok in Legoland.
Here’s a sense of how it works. The problem of factorisation is to find a number that divides exactly into another. Mathematicians do this using the idea of periodicity: a mathematical object with exactly the right periodicity should divide the number exactly, any others will not.
One way to study periodicity in the classical world is to use fourier analysis, which can break down a signal into its component waves. The quantum analogue to this is the quantum fourier sampling and Shor’s triumph was to find a way to use this idea to find the periodicity of the mathematical object that reveals the factors.
Thanks to Shor, any code that relies on this kind of asymmetry (ie almost all popular public key encryption systems) can be cracked using a quantum fourier attack.
The McEliese cryptosystem is different. It too is asymmetric but its security is based not on factorisation but on a version of a conundrum that mathematicians call the hidden supgroup problem. What Dinh and buddies have shown is that this problem cannot be solved using quantum fourier analysis. In other words it is immune to attack by Shor’s algorithm. In fact, it is immune to any attack based on quantum fourier sampling.
That’s a big deal. It means that anything encoded in this way will be safe when the next generation of quantum computers start chomping away at the more conventional public key cryptosystems. One such system is Entropy, a peer-to-peer communications network designed to resist censorship based on the McEliese cryptosystem.
But Entropy is little used and there are good reasons why others have resisted the McEliese encryption system. The main problem is that both the public and private keys are somewhat unwieldy: a standard public key is a large matrix described by no fewer than 2^19 bits.
That may seem less of a problem now. It’s possible that the McEleise system will suddenly become the focus of much more attention more than 30 years after its invention.
However, it’s worth pointing out that while the new work guanratees safety against all known quantum attacks, it does nothing of the sort for future quantum attacks. It’s perfectly possible that somebody will develop a quantum algorithm that will tear it apart as easily as Shor’s can with the RSA algorithm. “Our results do not rule out other quantum (or classical) attacks,” says Dinh and co.
So s more likely scenario for future research is that crytpographers will renew their efforts in one of the several other directions that are looking fruitful, such as lattice-based algorithms and multivariate cryptography.
Either way, expect to hear a lot more about post quantum cryptography–provided the powers that be allow.
Ref: arxiv.org/abs/1008.2390 : The McEliece Cryptosystem Resists Quantum Fourier Sampling Attacks


Raman scattering or the Raman effect (pronounced: Template:IPA —) is the inelastic scattering of a photon. Discovered By Dr. C.V. Raman in liquids and by Grigory Landsberg and Leonid Mandelstam in crystals.
When light is scattered from an atom or molecule, most photons are elastically scattered (Rayleigh scattering). The scattered photons have the same energy (frequency) and wavelength as the incident photons. However, a small fraction of the scattered light (approximately 1 in 10 million photons) is scattered by an excitation, with the scattered photons having a frequency different from, and usually lower than, the frequency of the incident photons. In a gas, Raman scattering can occur with a change in vibrational, rotational or electronic energy of a molecule (see energy level). Chemists are concerned primarily with the vibrational Raman effect.
In 1922, Indian physicist Chandrasekhara Venkata Raman published his work on the "Molecular Diffraction of Light," the first of a series of investigations with his collaborators which ultimately led to his discovery (on 28 February 1928) of the radiation effect which bears his name. The Raman effect was first reported by C. V. Raman and K. S. Krishnan, and independently by Grigory Landsberg and Leonid Mandelstam, in 1928. Raman received the Nobel Prize in 1930 for his work on the scattering of light. In 1998 the Raman Effect was designated an ACS National Historical Chemical Landmark in recognition of its significance as a tool for analyzing the composition of liquids, gases, and solids.
Raman scattering: Stokes and anti-Stokes Edit
The interaction of light with matter in a linear regime allows the absorption or simultaneous emission of light precisely matching the difference in energy levels of the interacting electrons.
The Raman effect corresponds, in perturbation theory, to the absorption and subsequent emission of a photon via an intermediate electron state, having a virtual energy level (see also: Feynman diagram). There are three possibilities:
- no energy exchange between the incident photons and the molecules (and hence no Raman effect)
- energy exchanges occur between the incident photons and the molecules. The energy differences are equal to the differences of the vibrational and rotational energy-levels of the molecule. In crystals only specific photons are allowed (solutions of the wave equations which do not cancel themselves) by the periodic structure, so Raman scattering can only appear at certain frequencies. In amorphous materials like glasses, more photons are allowed and thereby the discrete spectral lines become broad.
- molecule absorbs energy: Stokes scattering. The resulting photon of lower energy generates a Stokes line on the red side of the incident spectrum.
- molecule loses energy: anti-Stokes scattering. Incident photons are shifted to the blue side of the spectrum, thus generating an anti-Stokes line.
These differences in energy are measured by subtracting the energy of the mono-energetic laser light from the energy of the scattered photons. The absolute value, however, doesn't depend on the process (Stokes or anti-Stokes scattering), because only the energy of the different vibrational levels is of importance. Therefore, the Raman spectrum is symmetric relative to the Rayleigh band. In addition, the intensities of the Raman bands are only dependent on the number of molecules occupying the different vibrational states, when the process began. If the sample is in thermal equilibrium, the relative numbers of molecules in states of different energy will be given by the Boltzmann distribution:
Thus lower energy states will have more molecules in them than will higher (excited) energy states. Therefore, the Stokes spectrum will be more intense than the anti-Stokes spectrum.
Distinction with fluorescenceEdit
The Raman effect differs from the process of fluorescence. For the latter, the incident light is completely absorbed and the system is transferred to an excited state from which it can go to various lower states only after a certain resonance lifetime. The result of both processes is essentially the same: A photon with the frequency different from that of the incident photon is produced and the molecule is brought to a higher or lower energy level. But the major difference is that the Raman effect can take place for any frequency of the incident light. In contrast to the fluorescence effect, the Raman effect is therefore not a resonant effect.
Selection rules Edit
A Raman transition from one state to another, and therefore a Raman shift, can be activated optically only in the presence of non-zero polarizability derivative with respect to the normal coordinate (that is, the vibration or rotation):
Raman-active vibrations/rotations can be identified by using almost any textbook that treats quantum mechanics or group theory for chemistry. Then, Raman-active modes can be found for molecules or crystals that show symmetry by using the appropriate character table for that symmetry group.
Stimulated Raman scattering and Raman amplificationEdit
Raman amplification can be obtained by using Stimulated Raman Scattering (SRS), which actually is a combination between a Raman process with stimulated emission. It is interesting for application in telecommunication fibers to amplify inside the standard material with low noise for the amplification process. However, the process requires significant power and thus imposes more stringent limits on the material. The amplification band can be up to 100 nm broad, depending on the availability of allowed photon states.
Raman spectrum generation Edit
For high intensity CW (continuous wave) lasers, SRS can be used to produce broad bandwidth spectra. This process can also be seen as a special case of four wave mixing, where the frequencies of the two incident photons are equal and the emitted spectra are found in two bands separated from the incident light by the phonon energies. The initial Raman spectrum is built up with spontaneous emission and is amplified later on. At high pumping levels in long fibers, higher order Raman spectra can be generated by using the Raman spectrum as a new starting point, thereby building a chain of new spectra with decreasing amplitude. The disadvantage of intrinsic noise due to the initial spontaneous process can be overcome by seeding a spectrum at the beginning, or even using a feedback loop like in a resonator to stabilize the process. Since this technology easily fits into the fast evolving fiber laser field and there is demand for transversal coherent high intensity light sources (i.e. broadband telecommunication, imaging applications), Raman amplification and spectrum generation might be widely used in the near future.
Raman spectroscopy employs the Raman effect for materials analysis. The frequency of light scattered from a molecule may be changed based on the structural characteristics of the molecular bonds. A monochromatic light source (laser) is required for illumination, and a spectrogram of the scattered light then shows the deviations caused by state changes in the molecule.
Raman spectroscopy is also used in combustion diagnostics. Being a completely non-intrusive technique, it permits the detection of the major species and temperature distribution inside combustors and in flames without any perturbation of the (mainly fluid dynamic and reactive) processes examined.
Stimulated Raman transitions are also widely used for manipulating a trapped ion's energy levels, and thus basis qubit states.
- Brillouin scattering
- Raman spectroscopy
- nonlinear optics
- fiber amplifier
- List of surface analysis methods
- Raman laser
- Surface Enhanced Raman Spectroscopy (SERS)
- "A new radiation", Indian J. Phys., 2 (1928) 387 - http://www.uky.edu/~holler/raman.html
- Herzberg, Spectra of Diatomic Molecules, Litton Educational Publishing, 1950, ISBN 0-442-03385-0, pp. 61ff and 66ff


Ultraclean carbon nanotubes hold promise for advances in optical fiber communications, solar cells and LEDs
Carbon atoms can assemble in numerous structural forms called allotropes, e.g. a diamond, graphite, or graphene. These forms can result in distinct properties for materials that consist of the same element. One such allotrope, a cylindrically structured molecule known as a carbon nanotube, has been the subject of much scientific research for the past twenty years because of its extraordinary tensile strength, unique electrical properties, and efficient heat conduction. It has well-established applications in nanoelectronics and more recently has attracted tremendous interest as a nanomaterial for next-generation optoelectronics (electronic devices that source, detect and control light for optical fiber communications, solar cells and LEDs) and quantum photonic devices that have the potential to revolutionize information processing, telecommunications, sensing and measurement.
Despite the promise of this innovative material, its light emission has generally been dimmer than theorists had expected. The majority of experiments on carbon nanotubes to date reveal low quantum efficiencies as well as dependence on the environment and chemical processing. This is detrimental to their usefulness in devices and other applications. According to Dr. Stefan Strauf, Professor in the Department of Physics and Engineering Physics and Director of the NanoPhotonics Laboratory at Stevens Institute of Technology, “Understanding the intrinsic photophysical properties of carbon nanotubes is very interesting scientifically and also essential to realizing efficient devices.”
To address these inefficiencies, Dr. Strauf and collaborators James Hone and Chee Wei Wong from Columbia University have devised an improved fabrication process for carbon nanotubes, potentially leading to brighter light sources and more effective solar cells based on the material. They were able to increase the spontaneous light emission from an individual carbon nanotube by two orders of magnitude compared to previously reported experiments. They were also able to achieve a fourfold prolonged coherence time of the light emission. The results of their work, titled “Prolonged Spontaneous Emission and Dephasing of Quantum Dot Excitons in Air-Bridged Carbon Nanotubes,” were published in the July 11 edition of Nature Communications (Issue 4, Article Number 2152, doi:10.1038/ncomms3152).
“Dr. Strauf’s groundbreaking advances with carbon nanotubes represent a significant scientific breakthrough that could herald technological innovation in numerous important industries such as quantum computing and solar energy,” says Dr. Michael Bruno, Dean of the Charles V. Schaefer, Jr. School of Engineering and Science.
Previous experiments have reported carbon nanotubes with spontaneous light emission times on the picosecond scale, while theorists had predicted intrinsic optical lifetimes of several nanoseconds. Dr. Strauf and his collaborators surmised that this disparity was due to masking caused by impurities in the material, which are the result of contamination from the substrate (material upon which the experimental processes take place) and surfactant (a chemical that works like a detergent to separate and disperse nanotubes in order to prevent clumping). The researchers therefore used sophisticated techniques to grow and arrange carbon nanotubes in order to mitigate unintentional impurities and reveal the true extent of the material’s optical capabilities. They prepared about 1,000 pairs of pillar posts, each 3 micrometers apart, in a silicon wafer and topped them with a metal catalyst. They then deposited the carbon in the form of an ambient chemical vapor and intensely heated the preparation, creating many carbon nanotubes that bridged the pillars. The growth suspended in air prevents the substrate and surfactant from blending into the nanotubes and diminishing their effectiveness. They also heated the nanotubes for shorter periods (2-10 minutes) than previous experiments. The shorter heating times meant less residual amorphous carbon, resulting in ultraclean nanotubes that emit a much brighter.
Carbon nanotubes have attracted great interest for optoelectronics because of the unique ability of the material to maintain the stability of electron states called excitons even at room temperature, as opposed to the extreme cold usually required. An exciton comes about when a (negatively charged) electron in a carbon nanotube is excited (raised to a higher energy level) but remains bound to a positively charged “hole” in the lower energy level. The exciton thus carries energy but not a net electric charge. Photons are absorbed when the electron enters the exciton state and light is emitted when the electron recombines with the hole. The emission can be used to create devices like LEDs, lasers, and quantum light sources, while the absorption can be used to create solar cells or photodetectors.
While the prolonged radiative emission is promising for device applications, the researchers also were able to maintain a longer coherence time of the emitted light from the exciton recombination in these individual carbon nanotubes, finding four-fold prolonged values compared to previous ensemble measurements. This discovery could spark new discussions about the nature of the underlying mechanism which causes the dephasing that makes it difficult to sustain quantum effects long enough to allow for practical quantum information processing. A breakthrough in preserving coherence could lead to quantum computers with unprecedented power, allowing researchers to approach unwieldy problems and rendering most cryptography obsolete.
According to Dr. Rainer Martini, Director of the Department of Physics and Engineering Physics, “This work constitutes a major advance in carbon-nanotube based photonics and will generate even more interdisciplinary inquiry in this field.”
Find out how to become a part of groundbreaking scientific research and innovative technologies in the Department of Physics and Engineering Physics at Stevens, or apply at Undergraduate Admissions or Graduate Admissions.


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Quantum computing may well be the future of most high-end data centres. This is because, as the demand to intelligently process a growing volume of online data grows, so the limits of silicon chip microprocessors are increasingly going to be reached. Sooner or later it will also become impossible to miniaturize traditional computing components further and hence to continue to achieve year-on-year increases in computer power. Today, Intel's latest microprocessors are based on an industrial process that can produce transistors only 22 nanometres wide. Further advancements in this technology are still possible. But at some point miniaturization will hit a physical limit as transistors only a few atoms in size will simply not be able to function.
Enter quantum computing -- an emerging science that quite literally goes beyond the laws of conventional physics. Over the next few decades, quantum computing could be the next-wave development to deliver computer power well beyond current comprehension. Today, all of us increasingly cast digital data shadows each time we use the Internet, or even when we pass a CCTV or other camera linked into a vision recognition system. At present there is simply no way to process all of the data that every person on the planet produces. But as quantum computers arrive, the opportunity to do this may well arrive. Read on to learn more about quantum computing -- and/or watch my Explaining Quantum Computing video.
Conventional computers are built from silicon chips that contain millions or billions of miniature transistors. Each of these can be turned "on" or "off" to represent a value of either "1" or "0". Conventional computers subsequently store and process data using "binary digits" or "bits". In contrast, quantum computers work with "quantum bits" or "qubits". These are represented in hardware using quantum mechanical states rather than transistors that are turned "on" or "off". For example, quantum computers may use the spin direction of a single atom to represent each qubit, or alternatively the spin direction of a single electron or the polarization orientation of a photon. Yet other quantum computing designs supercool rare metals to allow qubits to be represented by the quantum spin of a tiny magnetic field.
Due to the peculiar laws of quantum mechanics, individual qubits can represent a value of "1", "0" or both numbers simultaneously. This is because the sub-atomic particles used as qubits can exist in more than one state -- or "superposition" -- at exactly the same point in time. By attaching a probability to each of these states, a single qubit can therefore process a wide range of values. In turn, this allows quantum computers to be orders of magnitude more powerful than their conventional, purely digital counterparts.
The fact that qubits are more "smears of probability" than definitive, black-and-white certainties is exceptionally weird. Flip a coin and it cannot come up both heads and tails simultaneously, and yet the quantum state of a qubit can in some senses do just that. It is therefore hardly surprising that renowned nuclear physicist Niels Bohr once stated that "anyone who is not shocked by quantum theory has not understood it!"
Another very bizarre thing is that the process of directly observing a qubit will actually cause its state to "collapse" to one or other of its superpositions. In practice this means that, when data is read from a qubit, the result will be either a "1" or a "0". When used to store potentially infinite amounts of "hidden" quantum data, qubits can therefore never be directly measured. This means that quantum computers need to use some of their qubits as "quantum gates" that will in turn manipulate the information stored and processed in other hidden qubits that are never directly measured or otherwise observed.
Because qubits can be used to store and process not just the digital values of "1" and "0", but also many shades of grey in between, quantum computers have the potential to perform massively parallel processing. This means that quantum computers will be very effective at performing tasks -- like vision recognition, medical diagnosis, and other forms of artificial intelligence processing -- that can depend on very complex pattern matching activities way beyond the capabilities of both traditional computers and most human beings.
OK, so quantum computing may sound all very theoretical (and indeed at present a lot of it actually is!). However, practical quantum computing research is now very much under way. Perhaps most notably, back in 2007 a Canadian company called D-Wave announced what it described as "the world's first commercially viable quantum computer". This was based on a 16 qubit processor -- the Rainer R4.7 -- made from the rare metal niobium supercooled into a superconducting state. Back in 2007, D-Wave demonstrated their quantum computer performing several tasks including playing Sudoku and creating a complex seating plan.
Many people at the time were somewhat sceptical of D-Wave's claims. However, in December 2009, Google revealed that it had been working with D-Wave to develop quantum computing algorithms for image recognition purposes. Experiments had included using a D-Wave quantum computer to recognise cars in photographs faster than possible using any conventional computer in a Google data centre. Around this time, there was also an announcement from IBM that it was rededicating resources to quantum computing research in the "hope that a five-year push [would] produce tangible and profound improvements".
In 2011, D-Wave launched a fully-commercial, 128-qubit quantum computer. Called the D-Wave One, this is described by the company as a "high performance computing system designed for industrial problems encountered by fortune 500 companies, government and academia". The D-Wave One's super-cooled 128 qubit processor is housed inside a cryogenics system within a 10 square meter shielded room. Just look at the picture here and you will see the sheer size of the thing relative to a human being. At launch, the D-Wave One cost $10 million. The first D-Wave One was sold to US aerospace, security and military giant Lockheed Martin in May 2011.
D-Wave aside, other research teams are also making startling quantum computing advances. For example, in September 2010, the Centre for Quantum Photonics in Bristol in the United Kingdom reported that it had created a new photonic quantum chip. This is able to operate at normal temperatures and pressures, rather than under the extreme conditions required by the D-Wave One and most other quantum computing hardware. According to the guy in charge -- Jeremy O’Brien -- his team’s new chip may be used as the basis of a quantum computer capable of outperforming a conventional computer "within five years".
Another significant quantum computing milestone was reported in January 2011 by a team from Oxford University. Here strong magnetic fields and low temperatures were used to link -- or "quantumly entangle" -- the electrons and nuclei of a great many phosphorous atoms inside a highly purified silicon crystal. Each entangled electron and nucleus was then able to function as a qubit. Most startlingly, ten billion quantumly entangled qubits were created simultaneously. If a way an be found to link these together, the foundation will have been laid for an incredibly powerful computing machine. In comparison to the 128 qubit D-Wave One, a future computer with even a fraction of a 10 billion qubit capacity could clearly possess a quite literally incomprehensible level of processing power.
Quantum computing is a highly complex and bewildering field with incredible potential (though so too was microelectronics in the 1970s and we all now take that for granted!). For a far more technical overview of the topic, try reading this overview from Stanford University. You may also want to look at IBM's Quantum Computing pages, visit the Australian Centre of Excellence for Quantum Computation and Communication Technology, or browse-on-over to D-Wave's Technology Overview. Do be aware, however, that delving into any and all of these resources may well make your head hurt!
Ultimately, few companies and individuals will ever own a quantum computer. Nevertheless, within a decade or two most companies and individuals are very likely to be regularly accessing quantum computers from the cloud. Not least this is because one of the first mainstream applications of quantum computing will be in online security and data encryption. Today, all online security systems rely on prime number calculations that quantum computers are potentially very good at indeed. Fairly soon, anybody with a quantum computer will therefore theoretically be able to use it to crack the security on any bank account or cloud computing resource. The only way to prevent this will be to protect and encrypt all online resources with quantum security gateways. The demand for every bank and cloud provider to invest in a quantum computer -- if only for encryption purposes -- is therefore likely to skyrocket once the technology moves beyond its currently rather costly and cumbersome experimental phase. Almost certainly signalling the potential significance of quantum computing in code-making and code-breaking, in March 2012 the National Security Centre in the United States announced that it is spending $2bn on a highly-fortified data centre with a 512 qubit quantum computer.
Another major application area for quantum computing will be in the processing of Big Data. As the volume of digital data produced on Planet Earth continues to grow expotentially, so a significant potential exists to generate business and social value via its insightful interlinkage. While technologies like Hadoop are currently permitting advancements in the processing of vast data sets, it may well be the development of quantum computers that really pushes large-scale Big Data analysis into the mainstream.
For more information on quantum computing, you may like to watch my Quantum Computing Video. Information on a range of other future technologies can also be found on our sister site ExplainingTheFuture.com.


Mar 18, 2012
Into to Quantum Computing
Score: 4.2/5 (189 votes)
This is by no means comprehensive, I was limited to 5 pages when writing this. But hopefully you'll understand a bit about the physics behind quantum computing, and some of the applications of it. At the very least, it'll be a reference point if you want to do further research.
NOTE: There wasn't a good category for this, so it is now a how-to article :D Works cited is in the file attached.
“Classical” computers all follow a similar design. They are based on the von Neumann architecture, and all exhibit what is known as the “von Neumann Bottleneck”. This basically means that current computers, without the use of the parallel programming, can only perform one action at a time. With current processors, this is works fine for most tasks. Processors can currently execute millions of instructions every second, and that number is constantly rising. Why is there a need for an alternate technology then? With Moore's Law stating that the density of integrated chips will double about every eighteen months, there does not seem to be much need to change. Eventually engineers are going to hit a limit as to how much they can put onto these chips. Transistors can only get so small. Not to mention Rock's Law, which states that the cost to build the plants to produce these chips will double every four year. So with the rising price of production and chip density reaching its limit, where do computers go next? There are numerous alternatives that have been theorized, the most promising and interesting of these is quantum computing.
History of Quantum Computation
The theory of quantum mechanics has been around for almost 200 years, but it is only been the last 30 years that these principles have been thought to be applied to computing. Many people credit Peter Shor as being the father of quantum computation. He was the first person to bring quantum computing theory to more of a reality with his algorithm, known as Shor's algorithm, but he was not the one to have the initial idea of quantum computers. The man who is credited with being the first to mention a quantum computer was Richard Feynman. He addressed the issue of classical computers not being well suited at simulating real world physics. His idea on how to fix this issue was to create a computer primarily of quantum mechanical elements which would obey quantum laws. A couple of other key figures in the development of quantum computation were Steve Wiesner and David Deutsch. Wiesner was a leading figure in looking at quantum cryptography and applied the uncertainty principle to this. David Deutsch showed that any physical property could be modeled perfectly in a quantum computer.
Quantum Physics for Computation
The main concept behind quantum computing is the qubit. A qubit is similar to a bit yet very different. A bit is restricted values of 0 and 1 only, and a qubit can represent also 0 and 1, but it can also represent or a superposition of both 0 and 1. The idea of superposition states that a quantum particle can exist partly in all of its possible states at once. This is what makes quantum computation so interesting. Superposition is what gives a quantum computer its parallelism, or ability to work on many computations at a single time. For example, according to Deutch, a 30 qubit computer would theoretically be able to operate at ten teraflops, or ten trillion floating-point operations every second! Classical computers today operate at gigaflop speed, or billions of floating-point operations per second. But this also happens on much more than 30 bits. A problem with this theory is that the moment a qubit is looked at in superposition, it will assume the value of either 1 or 0, essentially making it a fancy bit. It is also possible to accidentally “bump” a qubit when trying to look at it and change its value. The fix to these issues is another important concept in quantum theory known as quantum entanglement. Entanglement states that if some outside force is applied to two atoms, they will become entangled and one atom will assume the properties of the other atom. This allows physicists to look at an atom by looking at its entangled counterpart, removing the risk of “bumping” the atom holding your value. Without entanglement, quantum computers would be nothing but a really expensive and complicated digital computer.
Implications for Computer Scientists
Perhaps the most interesting aspect of quantum computing to computer scientists is how it affects algorithms and algorithm design. Quantum algorithms could solve some problems exponentially faster than any current technology algorithm and could solve any other problem at least as fast as current technology. One example of what quantum computers could solve much faster is number factorization. With current technology, factoring large numbers is computationally infeasible and this is off what RSA encryption is based. The ability of quantum computing to factor numbers much faster than classical computing has been demonstrated with Shor's Algorithm. Shor's Algorithm was demonstrated the first time in 2001 by a group at IBM. They used a quantum computer with seven qubits to factor out 15, which is the smallest number able to be factored by this algorithm. A reason why some calculations are much faster on a quantum computer is parallelism. Currently, parallel computing happens through the use of extra hardware and multiple computers, but with quantum computing it could all be done in a single processor. For example, if one takes one qubit in superposition and performs some calculation with yet another qubit in the same superposition, one would have four results. It would output 0/0, 0/1, 1/0, and 1/1 results. If one takes two qubits and perform an operation on two other qubits, one would get 00/00, 01/00, 10/00, 11/00, 00/01, 00/10, and so on results.
Pros and Cons of Quantum Computing
Quantum computing can have an interesting impact on the technology world. The most intriguing benefit is likely to be the inherit parallelism that quantum computing brings. Being able to perform exponentially more calculations at any given time compared to classical computers is important. The quantum parallelism can be considered both beneficial and consequential. Because of this parallelism, a quantum computer would be able to factor large numbers in a reasonably short amount of time, a task that is currently infeasible. The issue here is that some encryption techniques that keep a lot of important information safe, are based on the fact that factoring large numbers is currently infeasible. A quantum computer could very easily break any encryption protocol that relies on large numbers being extremely difficult to factor. This could, in theory, make all of this information no longer protected. Another benefit that comes from the quantum parallelism is being able to search large databases much faster than today. One other benefit that comes from quantum computing is true randomness. Currently in computers, random numbers are generated through a complex algorithm, so only pseudo-random numbers can be produced. One of the core concepts of quantum mechanics is the inherit randomness. For example, if a single photon is shot at a beam splitter, that photon will go one of two ways at an equal 50/50 chance. There is no way of determining exactly which way it will go, only an educated guess can be made. Aside from the benefits of quantum computing, there are some downsides to it. The obvious con being the sheer cost and complexity of developing them. In 2005, the research team of Rainer Blatt succeeded in creating a computer with a fourteen qubit register. So there is still a lot of time needed to see a practical quantum computer be made. There is just too much that can go wrong in the quantum world.
Quantum computing is very interesting to think about because the possible advantages to it, but currently it is just too complex and error prone to become a practical system, however physicists are making a lot of progress in solving these issues. So what might a future of quantum computing look like? Quantum computers will not become the new PC, at least for quite a long time. But there will likely be large quantum computers that act as a server system. The personal computer world and Internet world have already become one, so having a series of “cloud” quantum computers spread out that people can connect to in order to perform some complex calculations is very believable. It is too early to say how much the average user will gain from advancements in this field, but it will definitely help large corporations and the science world. It would lead to advancements in the understanding of the quantum world in general. A quantum computer acting as a server would be near immune to denial of service attacks due to the amount of traffic a quantum computer with just a few hundred qubits could handle. This would also mean less servers would be needed to handle the world's traffic.
Current technology can only advance so far. Transistors have been made smaller and smaller each year since their inception, but they can only be so small before they reach the atomic size. Once this scale is hit, transistor technology will have hit its maximum potential. There are researchers working on possible solutions to this, but quantum computing has generated most of the attention. The sheer computing power that could be gained from using a relatively small amount of quantum bits is astounding. All this power can also lead to problems. A lot of the world's financial information is encrypted using a technique of generating large numbers that are not plausible to factor back down using current technology. With this new power our encryption system could be broken in a day. There may be some consequences of quantum computing, but the benefits can be seen to outweigh them. The next generation of computing is being made right now.


July 4, 2012
Scientists Make Strides Toward Quantum Computing
Lee Rannals for redOrbit.com - Your Universe Online
Harvard scientists claim that they have solved a problem faced in quantum computing by using diamonds.
One challenge quantum computing has faced is creating quantum bits that exist in a solid-state system at room temperature. Most systems rely on complex and expensive equipment designed to trap an atom or electron in a vacuum, and then cool the entire system to nearly absolute zero, or –459.67° Fahrenheit.
The Harvard team used a pair of impurities in laboratory-grown diamonds to create quantum bits, or qubits, and store information in them for nearly two-seconds.
Although two-seconds doesn't seem like a long time, it is actually an increase of nearly six orders of magnitude over the life span of earlier systems.
The scientists wrote in the journal Science that this is a first step in the eventual construction of a functional quantum computer.
"What we´ve been able to achieve in terms of control is quite unprecedented," Professor of Physics Mikhail Lukin, leader of the research, said. "We have a qubit, at room temperature, that we can measure with very high efficiency and fidelity."
He said the work is limited only by technical issues, so it would be feasible to increase the life span into the range of hours.
"At that point, a host of real-world applications become possible," Lukin said.
He said he envisions the system being used in applications that include "quantum cash," which is a theoretical payment system for bank transactions and credit cards that rely on coding of quantum bits to keep counterfeiters at bay. Another application, according to Lukin, would be for "quantum networks," which is a highly secure communications method that uses quantum bits to transmit data.
"This research is an important step forward in research toward one day building a practical quantum computer,” graduate student Georg Kucskoo, who works in Lukin´s lab and is one of two first authors of the paper, said. "For the first time, we have a system that has a reasonable timescale for memory and simplicity, so this is now something we can pursue."
During the initial experiments, the team used diamonds that contained 99 percent carbon-12 atoms, which have no spin. However, the remainder was made up of carbon-13 atoms, which is a tricky isotope that contains a spin in the atom's nucleus.
“The nuclear spin of the carbon-13 makes an ideal quantum bit, because they are very isolated,” Lukin said. “Because they interact with so few outside forces, they have relatively long coherence times. Of course, the same properties that make them ideal qubits also make them difficult to measure and manipulate.”
The team decided that rather than trying to find a way to measure the spin of the carbon atoms, they would use the nitrogen-vacancy (NV) centers, which are atomic-scale impurities in lab-grown diamonds, to do it for them.
They developed a new technique to create crystals that were even more pure, and then bombarded the crystal with nitrogen to create the NV center.
The interaction resulted in the NV center mirroring the state of the carbon atom, which means the researchers can encode a bit of information into the spin of the atom, then "read" that data by monitoring the NV center.
“The system we´ve developed uses this very local probe, the NV center, to allow us to monitor that spin,” Lukin said. “As a result, for the first time, we can encode a bit of information into that spin, and use this system to read it out.”
However, encoding information into the spin of the carbon-13 atom and reading it using the NV center is only a first step. The team had to determine how to take advantage of the atom's quantum properties as well.
Being able to be in two states at the same time is a key principle in quantum computers. Traditional computers encode bits of information as either zero or one, while quantum computers rely on atomic-scale quantum mechanics to give quantum bits both values at once.
That property allows quantum computers to perform multiple computations in parallel, making them more powerful than traditional computers.
The first step, according to Lukin, is to cut the connection between the NV center and the carbon atom by using massive amounts of laser light.
The second step is that the diamond crystal is bombarded with a specific set of radio frequency pulses, which suppresses the interaction between the carbon-13 atom and nearby atoms.
“By limiting interactions with the carbon-13 atom, we can extend the life of the qubit and hold the data for longer,” Lukin said. “The end result is that we´re able to push the coherence time from a millisecond to nearly two seconds.”


It might seem like something straight from the Star Trek universe, but two new research experiments—one involving a photon and the other involving a super-conducting circuit—have successfully demonstrated the teleportation of quantum bits.
If that sounds like gobbledygook, don't worry. We got in touch with one of the researchers, physicist Andreas Wallraff, of the Quantum Device Lab at the Swiss Federal Institute of Technology Zurich, to explain how his team and a team based at the University of Tokyo were able to reliably teleport quantum states from one place to another.
People have done this before but it hasn't necessarily been reliable. The new complementary research, which comes out in Nature today, is reliable—and therefore may have widespread applications in computing and cryptography.
Before we talk about the nitty-gritty part of teleportation, we need to define a few key words. Let's start with a regular, classical bit of information, which has two possible states: 1 or 0. This binary system is used by basically all computing and computing-based devices. Information can be stored as a 1 or a 0, but not as both simultaneously. (Related: "The Physics Behind Schrodinger's Cat.")
But a quantum bit of information—called a qubit—can have two values at the same time.
"With the qubit, you can store more information because you have information in all of its possible states," Wallraff says. "Whereas in the classical memory system, only one can be stored." (More physics: "The Physics Behind Waterslides.")
Quantum teleportation relies on something called an entangled state. An entangled state, in the words of Wallraff, is a "state of two quantum bits that share correlations." In other words, it's a state that can't be separated.
If you have a classical 1 and a 0, for example, you can separate them into a 1 and a 0. But if you have qubits, the bits can be assigned both a 1 and a 0 at the same time—meaning they can't be separated into their individual components and must be described relative to each other. (If you'd like to know more about this, I recommend delving into "Quantum Entanglement" on the Caltech website.)
Diving Into Teleportation
Now that we have a small working vocabulary, we can delve into what Wallraff and team actually did.
Let's go back to Star Trek.
"People automatically think about Star Trek when they hear teleportation," says Wallraff. "In Star Trek, it's the idea of moving people from point A to B without having the person travel that distance. They disappear and then reappear."
What happens in quantum teleportation is a little bit different. The bits themselves don't disappear, but the information about them does.
"That's where the relation to Star Trek comes in," says Wallraff. "You can make the information disappear and then reappear at another point in space."
So how does this work? Remember, we're talking about quantum bits—which can hold two possible states at the same time.
"You can ask yourself, 'How can I transport the information about this bit from one place to another?'" says Wallace. "If you want to send the information about the qubit from point A to B, the information at point A [contains] 0 and 1 simultaneously."
It's impossible using classical bits to transmit this information because, as we learned earlier, the information can be stored as 1s or 0s but not both. Quantum teleportation gets around this problem. (Related: "Physicists Increasingly Confident They've Found the Higgs Boson.")
This is where those entangled states I mentioned earlier come into play. In quantum teleportation, a pair of quanta in an entangled state is sent to both a sender—which I'll call A—and a receiver—which I'll call B. A and B then share the entangled pair.
"The sender takes one of the bits of the entangled pair, and the receiver takes the other," says Wallraff. "The sender can run a quantum computing program measuring his part of the entangled pair as well as what he wants to transport, which is a qubit in an unknown state."
Let's untangle what he said: The sender—A—makes a measurement between his part of the entangled pair and what he wants to transport.
Back to you, Wallraff.
"So we have this measurement, and that's what is sent to the receiver via a classical bit," he says.
The receiver—B—receives the measurement between A's part of the entangled pair and the unknown qubit that A wants to send. After B receives this measurement, he runs a quantum computing algorithm to manipulate his part of the entangled pair in the same way. In the process, B re-creates the unknown qubit that A sent over—without receiving the qubit itself.
I realize this is confusing.
But Why Is It Useful?
The advances these two research groups have made may improve the way quantum bits are sent, leading to faster processors and larger-scale encryption technologies.
Encryption technology—which is used by everyone from credit card companies to the NSA—is based on the fact that it's really, really hard to find factors of very large prime numbers. And quantum computing is extremely useful for factoring very large prime numbers.
Dividing or multiplying numbers is fairly easy for any computer, but determining the factors of a really large 500- or 600-digit number is next to impossible for classical computers. But quantum computers can process these numbers easily and simultaneously.
Credit card companies, for instance, assign users a public key to encode credit card information. The key is the product of two large prime numbers, which only the website seller knows. Without a quantum computer, it would be impossible to figure out the two prime numbers that are multiplied together to make the key-which protects your information from being shared. (For more info, read this really useful guide about the basics of quantum computing from the University of Waterloo.)
"If you wanted to use classical bits to do this, it wouldn't be efficient," says Wallraff. In other words, classical computers—the ones we use now for most stuff—can't do any of the things quantum computers can do on a large scale.
So while we might not be beaming Scotty up just yet, our computers, it appears, are one step closer to doing so.


A New Era for Atomic Clocks (page 2)
NIST's Atomic Clocks
All clocks must have a regular, constant or repetitive process or action to mark off equal increments of time. Examples include the daily movement of the sun across the sky, a swinging pendulum or vibrating crystal. In the case of atomic clocks, the beat is kept by a transition between two energy levels in an atom.
NIST-F1 and NIST-F2 are microwave clocks, based on a particular vibration in cesium atoms of about 9 billion cycles per second. Optical atomic clocks are based on ions or atoms vibrating at optical frequencies (visible, ultraviolet or infrared light), which are about 100,000 times higher than microwave frequencies. Because optical clocks divide time into smaller units—like a ruler with finer tick marks—they ultimately could be perhaps 100 times more accurate and stable than microwave clocks. Higher frequency is one of the features enabling improved accuracy and stability. One key advance making optical atomic clocks possible was the development of frequency combs at JILA, NIST and elsewhere. Frequency combs link optical frequencies to lower frequencies that can be correlated with microwave standards and counted.
NIST's first all-optical atomic clock, and the best in the world for several years, was based on a single mercury ion. Its performance was then surpassed by NIST's quantum logic clock, based on a single aluminum ion. This clock got its nickname because it borrows techniques from experimental quantum computing. Aluminum is insensitive to changes in magnetic and electric fields and temperature, making it a great ion for atomic clocks, but it wasn't practical until NIST developed new quantum computing technologies.
NIST and JILA are leaders in the development of so-called optical lattice clocks. These clocks trap thousands of heavy metal atoms in an "optical lattice" formed by intersecting laser beams. Research clocks at NIST use ytterbium atoms and JILA research clocks use strontium atoms. Thanks to the presence of so many atoms, these clocks offer the advantages of strong signals and parallel processing. In addition, the atoms are held virtually still in the lattice, reducing errors from atomic motion and collisions that otherwise would need to be corrected.
Optical lattice clocks are rapidly improving, and continue to set new performance records so often that it is difficult to keep track of the latest records. Both the JILA strontium and NIST ytterbium optical lattice clocks are rapidly advancing in stability. And now, for the first time in decades, a single type of atomic clock, an optical lattice clock, simultaneously holds the records for both precision and stability – and it is likely optical lattice clock performance will continue to significantly improve.
This rapid improvement in optical lattice clocks at JILA and NIST results from key scientific breakthroughs. One has been the development of extremely stable lasers, including the world's most stable laser at JILA. Another key breakthrough has been development of new theories about how atoms trapped in the optical lattices interact, and application of these theories to significantly reduce the uncertainties in optical lattice clocks. And much of the improvement results from the hard and creative work of many scientists, students and postdoctoral fellows to continually find new ways to make a series of many small improvements in clock performance.
NIST also has demonstrated a calcium atomic clock that is extremely stable for short time periods. This clock has the potential to be made portable, making it attractive for commercial applications.
Evaluating Atomic Clock Performance
Accuracy refers to a clock's capability to measure the accepted value of the frequency at which the clock atoms vibrate, or resonate. Accuracy is crucial for time measurements that must be traced to primary standards such as NIST-F1 and NIST-F2. Technical terms for accuracy include "systematic uncertainty" or "fractional frequency uncertainty"—that is, how well scientists can define shifts from the true frequency of an atom with confidence.
Cesium standards like NIST-F1 and NIST-F2 are the ultimate "rulers" for time because the definition of the SI second is based on the cesium atom. More specifically, the SI unit of frequency, the Hertz, is defined internationally by the oscillations of a cesium atom. Officially, no atomic clock can be more accurate than the best cesium clock by definition. That is, only a direct measurement of the particular cesium transition can be considered the ultimate measurement of accuracy, and all other (non-cesium) clocks can only be compared to the accuracy of a cesium clock. This is partly a semantic issue. If after further development and testing the definition of the second (or Hertz) were changed to be based on the strontium atom transition, for example, the NIST/JILA strontium atom lattice clock would become the most accurate clock in the world.
To get around this measurement hurdle, NIST scientists evaluate optical atomic clocks by comparing them to each other (to obtain a ratio, or relative frequency, for which there is no official unit), and by measuring all deviations from the true resonant frequency of the atom involved, carefully accounting for all possible perturbations such as magnetic fields in the environment. The optical clock performance is also directly compared to the NIST-F1 standard. For several years both NIST ion clocks have had measured relative uncertainties much smaller than NIST-F1's.
(In general literature, NIST sometimes uses the term "precise" to describe the performance of optical clocks, because it less technical and has a more positive connotation than uncertainty. Precision implies that repeated measurements fall within a particular error spread around a given value. In everyday definitions of precision, this value is not necessarily the "correct" one—you can be precise without necessarily being accurate. However, in the context of optical clocks, NIST uses precision specifically to mean the spread around the true or accepted value for the atom's resonant frequency.)
Stability is another important metric for evaluating atomic clocks. NIST defines stability as how precisely the duration of each clock tick matches every other tick. Because the ticks of any atomic clock must be averaged for some period to provide the best results, a key benefit of high stability is that optimal results can be achieved very quickly. Stability is not traceable to a time standard, but in many applications stability is more important than absolute accuracy. For example, most communications and GPS positioning applications depend on synchronization of different clocks, requiring stability but not necessarily the greatest accuracy. (Other common terms for stability include precision.)
The optical lattice clocks at NIST and JILA are much more stable than NIST-F1. NIST-F1 must be averaged for about 400,000 seconds (about five days) to achieve its best performance of about 1 second in 100 million years. In contrast, the ytterbium and strontium lattice clocks reach that level of performance in a few seconds of averaging, and after a few hours of averaging are about 100 times more stable than NIST-F1.
NIST scientists are also working to improve the portability of next-generation atomic clocks for applications outside the laboratory.


A Nov. 5, 2013 Vienna University of Technology press release (also available on EurekAlert) describes research that may make quantum optical switches possible,
With just a single atom, light can be switched between two fibre optic cables at the Vienna University of Technology. Such a switch enables quantum phenomena to be used for information and communication technology.
The press release goes on to describe a ‘light in a bottle’ technique which leads, the researchers hope, that they may have discovered how to create a quantum light switch,
Professor Arno Rauschenbeutel and his team at the Vienna University of Technology capture light in so-called “bottle resonators”. At the surface of these bulgy glass objects, light runs in circles. If such a resonator is brought into the vicinity of a glass fibre which is carrying light, the two systems couple and light can cross over from the glass fibre into the bottle resonator.
“When the circumference of the resonator matches the wavelength of the light, we can make one hundred percent of the light from the glass fibre go into the bottle resonator – and from there it can move on into a second glass fibre”, explains Arno Rauschenbeutel.
A Rubidium Atom as a Light Switch
This system, consisting of the incoming fibre, the resonator and the outgoing fibre, is extremely sensitive: “When we take a single Rubidium atom and bring it into contact with the resonator, the behaviour of the system can change dramatically”, says Rauschenbeutel. If the light is in resonance with the atom, it is even possible to keep all the light in the original glass fibre, and none of it transfers to the bottle resonator and the outgoing glass fibre. The atom thus acts as a switch which redirects light one or the other fibre.
Both Settings at Once: The Quantum Switch
In the next step, the scientists plan to make use of the fact that the Rubidium atom can occupy different quantum states, only one of which interacts with the resonator. If the atom occupies the non-interacting quantum state, the light behaves as if the atom was not there. Thus, depending on the quantum state of the atom, light is sent into either of the two glass fibres. This opens up the possibility to exploit some of the most remarkable properties of quantum mechanics: “In quantum physics, objects can occupy different states at the same time”, says Arno Rauschenbeutel. The atom can be prepared in such a way that it occupies both switch states at once. As a consequence, the states “light” and “no light” are simultaneously present in each of the two glass fibre cables. [emphasis mine]
For the classical light switch at home, this would be plain impossible, but for a “quantum light switch”, occupying both states at once is not a problem. “It will be exciting to test, whether such superpositions are also possible with stronger light pulses. Somewhere we are bound to encounter a crossover between quantum physics and classical physics”, says Rauschenbeutel.
This light switch is a very powerful new tool for quantum information and quantum communication. “We are planning to deterministically create quantum entanglement between light and matter”, says Arno Rauschenbeutel. “For that, we will no longer need any exotic machinery which is only found in laboratories. Instead, we can now do it with conventional glass fibre cables which are available everywhere.”
Darrick Chang offers a good introduction (i.e., it’s challenging but you don’t need a physics degree to read it) and some analysis of this work in his Nov. 4, 2013 article for Physics (6, 121 (2013) DOI: 10.1103/Physics.6.121) titled: Viewpoint: A Single-Atom Optical Switch.
Quantum scientists over the past two decades have dreamt of realizing powerful new information technologies that exploit the laws of quantum mechanics in their operation. While many approaches are being pursued, a prevailing choice consists of using single atoms and particles of light—single photons—as the fundamental building blocks of these technologies . In this paradigm, one envisions that single atoms naturally act as quantum processors that produce and interface with single photons, while the photons naturally act as wires to carry information between processors. Reporting in Physical Review Letters, researchers at the Vienna University of Technology, Austria, have taken an important step forward in this pursuit, by experimentally demonstrating a microphotonic optical switch that is regulated by just a single atom .
This article is open access.
For those willing to tackle a more challenging paper, here’s a link to and a citation for the Vienna University of Technology researchers’ paper,
Fiber-Optical Switch Controlled by a Single Atom by Danny O’Shea, Christian Junge, Jürgen Volz, and Arno Rauschenbeute. Phys. Rev. Lett. 111, 193601 (2013) [5 pages]
This work is behind a paywall.
Minutes after publishing: here’s an image that illustrates superpositioning in a quantum switch,


It's a machine that could calculate solutions to problems so impossibly time-consuming that even the most powerful supercomputers could never handle them. And it would do so in an instant. This is the quantum computer, made possible by the bizarre nature of quantum mechanics. And though the idea is still in its infancy, it's no fantasy.
Two research teams, at Harvard University and the Max Planck Institute of Quantum Optics in Germany, have just announced that they have independently forged the building blocks for tomorrow's quantum computers. As they published today in the journal Nature (1, 2), the scientists discovered a way to hook up atoms and particles of light to create a new type of switch and logic-gate‚ quantum versions of the connecting structures that link bits of data in modern computers.
When you dive down into the circuits, all modern computers are basically the same: a huge collection of data arranged with simple rules. Each piece of data is called a bit and shows just one fragment of information‚ a 0 or a 1. You can think of a bit as a lightbulb that's either shining or not.
But quantum theory‚ the physics that rules the tiny world of atoms and particles‚ tells us that there are certain circumstances in which a piece of matter can be two things at the same time. It's possible to have an atom that's spinning in two opposite directions at once, or even to have your lightbulb both shining and not shining. Items with this wacky dual state are said to be in "superposition." (Physicist Niels Bohr once said, "Those who are not shocked when they first come across quantum theory cannot possibly have understood it." So don't worry if you're confused‚ Bohr was one of the founders of quantum theory.)
The most important catch (there are plenty) is that this superposition state is fragile and possible only for incredibly tiny bits of matter.
But for computers, this very idea poses an interesting prospect. If you could somehow harness this odd state of matter to put individual bits of information into superposition, then suddenly you've packed more data into the tiniest package possible. Your bits can now show a 0, a 1, or a combo of both. This is called a quantum bit, or a qubit. And if qubits were linked together like normal bits are linked in a computer, then you'd have a machine could calculate at insane speeds.
"At this point, very small-scale quantum computers already exist," says Mikhail Lukin, the head of the Harvard research team. "We're able to link, roughly, up to a dozen qubits together. But a major challenge facing this community is scaling these systems up to include more and more qubits."
The problem of adding more qubits, Lukin explains, is tied to the fragility of the superposition state. Unless the entire quantum computer is kept at extremely cold temperatures and free of any interfering particles or other noise, the superposition state will entirely collapse for all the qubits, ruining the computer. What makes this even harder is that today's qubits must be close to one another to be connected, and it takes a massive apparatus of machinery, lab equipment, and lasers to support the superposition state of just a single fleck of matter. That dumps an increasing amount of grit into the system, increasing the chance that the entire quantum computer will fail.
"It's just very difficult to address one qubit without interfering with all the rest of them; to take a laser beam and shine it one particular qubit and not another," says Gerhard Rempe, the head of the Max Planck Institute of Quantum Optics research team. "And if, for example, you want to use 10,000 qubits, well, that's 10,000 lasers you have to worry about."
The Ol' Gate and Switch
The new quantum logic gate and switch unveiled today promise to ameliorate some of these problems. Both use a new method: They harness trapped atoms (in both cases, rubidium) that can transfer information through photons, the particles that make up light. Photons, which can be directed through fiber-optic cable, are the prime candidate for sending information at great distances and keeping qubits apart.
Here is how it works: The scientists trap a heavy rubidium atom between two mirror-like sheets using a laser technique that keeps the atom relatively immobile. The scientists then send a photon straight at this atom sandwich. Normally, the photon would hit the first mirror and bounce right back where it came from. But if the atom is put in a specific energetic state, the photon will go straight through that first mirror, hang out with the atom for a moment, and then exit where it came from. As a going-away present, the photon also has a slight change in polarization. This is pretty much how any switch in a computer works. If something is "on," then one thing happens. If it's "off," then another thing happens.
But here's the tricky part. The scientists can put the rubidium atom in superposition, so that it is simultaneously in that energetic state and not in the energetic state. It's on and off. Because of this, the photon both does and does not enter the mirror, mingle, and gain its polarization change. And the photon, by virtue of having both changed and not changed, carries that superposition information and can bring it to a different atom-based qubit.
A similar process happens with the quantum logic gate. A normal logic gate is just a series of switches set up in a way that together, they perform a logical operation when given multiple inputs. The German team created a quantum version by having multiple photons repeatedly bounce off the mirror-trapped and superpositioned rubidium atom. Then, using another funky attribute of quantum physics called entanglement swapping, the scientists made it so that the photons share the same information. These entangled photons can become the multiple inputs required for any logic gate.
Even with this new advancement, we're still a long way from building large-scale quantum computers, with thousands of qubits linked together. "We're not going to see quantum computers being built for the average American consumer in ten years, or anything like that," says Jeff Thompson, a physicist with the Harvard research team.
Rempe says that while this technology seems promising for solving the qubit-closeness issue, neither team is actually attempting to link multiple qubits. And that endeavor will probably open up a new world of unknowns.
Nonetheless, "It's exciting to see this [photon-based] technology is coming into its own," says Jacob Taylor, a physicist at the University of Maryland who was not involved with the projects. Whatever future difficulties arise, he says, scientists are learning valuable information about one of the most fundamental aspects of physics. Everything we know about quantum mechanics would lead us to believe that large-scale quantum computers should be theoretically possible. But even if "you couldn't build a large-scale quantum computer," he says, "that's somewhat exciting, too. That tells us that our theory of quantum mechanics might be breaking down somewhere, that we still have much to learn."


Physics student Brian Vlastakis GRD ’15 works in the lab of Yale applied physics professor Robert Schoelkopf, associate director of the Yale Institute for Nanoscience and Quantum Engineering. Vlastakis sat down with the News on Monday to discuss quantum computing.
Q: Can you briefly summarize the importance of quantum computing?
A: The idea for our field of quantum information and quantum computation is trying to manipulate quantum mechanics in order to perform very complicated computation algorithms. A classical computer is made up of very many digital bits that have a 0 or a 1 state. In a quantum computer, the bit is now acting quantum mechanically. A quantum mechanical bit — we call it a qubit — is forced to obey the laws of quantum mechanics, in the sense that it’s not just in one place at once. It can be both 0 and 1 at the same time, and the idea here is that you’re performing multiple calculations at once. A nice analogy that people like to use for quantum computers is that you’re kind of essentially doing the ultimate “parallel processing.” The quantum processor is sort of like having many classical processors all performing a calculation in parallel, doing separate smaller calculations and then putting them together.
Q: How does the lab that you’re working in contribute to quantum information?
A: We’re trying to build quantum computers, but there are many ways you can implement them. One way, what we do, is called superconducting qubits.
In quantum information, you want to be able to create quantum bits, which are essentially a system with ground-state energy, representing 0, and some excited-state energy level, representing 1. You want to be able to address the transition between these states. We’re trying to create these “two-level systems,” which is just another word for a quantum bit, and we’re creating them with superconducting circuits.
There are other crazy ways to make quantum bits, but what’s really nice about the way that we’re making these quantum bits is that we’re able to print them out on a circuit board. This is actually the same technique that big companies use to make regular computers. This makes the field that we’re in very exciting, because a lot of these companies say that if you guys can figure out how to control them and understand them, then we can make them.
Now, we’re slowly trying to put all these components together in order to perform very rudimentary quantum algorithms. What’s exciting is that these really have a great potential to scale up and become powerful quantum computers.
Q: How do you hope to expand to scaling up?
A: When you have only a few quantum bits, it’s okay if they mess up every once in a while, because the probability of only one messing up is pretty slim. But if you had a million of those bits, there’s a very good chance that one of them will mess up when you’re doing your algorithm. This is actually a very difficult thing for quantum algorithms, because quantum bits are extremely sensitive to errors that might occur to them. Unfortunately for these quantum bits, any fluctuation between the 0 and 1 states actually corresponds to a completely different quantum state.
So, we need to know precisely what state our bit is actually in. What this requires is something called quantum error correction. This is what almost everyone in quantum computation is striving to achieve. Being able to do quantum error correction will be the biggest stepping stone is scaling up to these very large scales of quantum bits. We’ll forever be stuck in these few qubit systems until we can sort out quantum error correction. So the big five-year goal in the field is to try to be able to perform rudimentary quantum error correction schemes.
Q: How will the work of your lab contribute to the quantum error correction?
A: What’s really great about using superconducting qubits is that they are circuits, so if we want to have one qubit interact with another qubit, we can just design a system where’s there’s just a wire that attaches them. This has a lot of really big advantages if we want to implement a type of quantum error correction. We can design a system where different qubits will only interact with other certain qubits. That’s one of the things we’re actively exploring right now.
The thing that I’m actually looking into is seeing if we can go beyond just using a quantum bit for these sorts of error correction schemes and regular quantum algorithms. So, something that I’m looking into is using a resonator. In quantum mechanics you have these two-level systems, and then what you call “harmonic oscillators” — or “resonators.” I’m trying to look if we can use cavity resonators as a resource for some sort of quantum memory.
There are many ways you can think of a cavity. Typically when we say “cavity” you think of photons, so a cavity resonator is just a box that’s trapping photons, and they’re forced to bounce back and forth inside this cavity. A typical one that most people think of is just two mirrors facing each other — if you send in light, you just get light that’s stuck bouncing back and forth. We can essentially create the same thing with these superconducting circuits.


pairs power quantum plan
Technology Research News
The shortest route to practical quantum
computers, which promise to be phenomenally powerful, may be through proven
manufacturing processes, namely the semiconductor technology of today's
computer chips. It wouldn't hurt if the machines also used aspects of
quantum physics that are relatively easy to control.
Researchers from Hewlett-Packard Laboratories and Qinetiq plc in England
have mapped out a way to manipulate a pair of very cold electrons that
could eventually lead to practical quantum computers made from quantum
dots, or tiny specks of the type of semiconductor material used in electronics.
The researchers showed that at low temperatures, a pair of trapped electrons
operate relatively simply and can be manipulated using electric and magnetic
fields. "For... two electrons in a square-shaped quantum dot, there are
just two states," John Jefferson, a senior fellow at Qinetiq.
The electrons repel each other to diagonally-opposite corners of the quantum
dot, leaving the two electrons in one of two possible configurations:
upper right corner and lower left corner, or upper left corner and lower
These two states can represent the 1s and 0s of digital information; the
quantum dots, or qubits, that contain them are the quantum computing equivalent
of today's computer transistors, which use the presence or absence of
electricity to represent 1s and 0s.
Quantum computers have the potential to solve very large problems fantastically
fast. The weird rules that quantum particles like atoms and electrons
follow allow them to be in some mix of states at once, so a qubit can
be a mix of both 1 and 0. This means that a single string of qubits can
represent every possible answer to a problem at once.
This allows a quantum computer to use one set of operations to check every
potential answer to a problem. Today's electronic computers are much slower,
in contrast, because they must check answers one at a time.
Key to the researchers method is the square shape of the microscopic quantum
dot -- a speck of the semiconductor gallium arsenide measuring 800 nanometers
a side -- that they used to trap the electrons. A nanometer is one millionth
of a millimeter. "Two electrons in a square quantum dot repel each other
[to the corners] due to the usual Coulomb repulsion force between them,"
The Coulomb force kicks in when particles carry a charge. Particles of
the same charge, like electrons, which are negatively charged, repel each
Due to the weird nature of quantum particles, however, the electron pair
may also jump, or tunnel, from one position, or state, to the other, said
Jefferson. "This happens periodically... and the system can also be in
a strange superposition state where it is partly in one state and partly
in the other," he said. "This is the basis of our two-electron semiconductor
The researchers showed that they could use voltage pulses and magnetic
fields to take this type of qubit through all the necessary operations
needed to compute, said Jefferson.
This was tricky because it is not possible to turn the Coulomb force on
and off, said Jefferson. "A severe potential problem with the Coulomb
interaction is that it is always there," he said. The researchers showed,
however, that it is possible to control the effects of the force, and
thus harness it to do computing.
The researchers scheme differs from many other quantum dot quantum computing
designs because it uses the positions of two electrons rather than their
spin, which is a quality that can be likened to a top spinning clockwise
or counterclockwise. The electrons' positions determine the charge states
of the quantum dot, meaning if an electron is in one corner of the quantum
dot that corner has a charge. "It is often easier to manipulate charge
states compared to spin states," said Jefferson. In addition, "it is...
certainly easier to measure charge states compared to spin states," he
To turn this building block into a practical computing device, however,
the qubits must be stable. This requires "some means of preparing the
qubits in a specific state, after which they have to [be affected only]
according to the basic laws of quantum mechanics," said Jefferson. This
includes isolating them from other interactions, he said.
Practical quantum computers would require hundreds or thousands of connected
qubits. "It should be possible to add more qubits," said Jefferson. There
must also be a way to measure the final results when the computation has
taken place, he said.
The researchers showed that these requirements can theoretically be satisfied
using the two-electron qubits, said Jefferson. "In principle, these criteria
may be met, though to do so in a practical device would be technologically
very challenging," he said.
Researchers generally agree that practical quantum computing of any type
is one to two decades away. "Ten to 20 years is more realistic than 2
to 5," for a practical application of the two-electronic quantum dots,
Rather than using semiconductor quantum dots, the researchers' basic method
could possibly be achieved more quickly and effectively using a series
of individual molecules, said Jefferson. "The energy and temperature scales
[for molecules] are higher and thus less prone to random errors," he added.
This could address one of the main hurdles to using qubits practically,
Jefferson said. "One of the main challenges is to reduce the interaction
of a quantum system with its environment -- the so-called decoherence
problem," he said.
The other main technical challenge to using the system practically would
be to produce quantum dots containing precisely two electrons, and to
coax the electrons to switch states with acceptable error rates, he said.
Jefferson's research colleagues were M. Fearn and D. L. J. Tipton of Qinetiq
and Timothy P. Spiller of Hewlett-Packard Laboratories. They published
the research in the October 30, 2002 issue of the journal Physical Review
A. The research was funded by the British Ministry of Defense, the European
Union, Hewlett-Packard and Qinetiq.
Timeline: 10-20 years
Funding: Corporate, Government
TRN Categories: Physics; Quantum Computing and Communications
Story Type: News
Related Elements: Technical paper, "Two-Electron Quantum
Dots as Scalable Qubits," Physical Review A, October 30, 2002.
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