Sunday, March 30, 2014

Quantum chaos in ultracold gas discovered

Quantum chaos in ultracold gas discovered


The team of Francesca Ferlaino, Institute for Experimental Physics of the University of Innsbruck, Austria, has experimentally shown chaotic behavior of particles in a quantum gas. "For the first time we have been able to observe quantum chaos in the scattering behavior of ultracold atoms," says an excited Ferlaino. The physicists used random matrix theory to confirm their results, thus asserting the universal character of this statistical theory. Nobel laureate Eugene Wigner formulated random matrix theory to describe complex systems in the 1950s. Although interactions between neutrons with atomic nuclei were not well-known then, Wigner was able to reliably predict properties of complex spectra by using random matrices. Today random matrix theory is applied broadly not only in physics but also in number theory, wireless information technology and risk management models in finance to name only a few fields of application. In the Bohigas-Giannoni-Schmit conjecture random matrix theory has been connected to chaotic behavior in quantum mechanical systems. Catalan physicist Oriol Bohigas, who passed away last year, can be considered the father of quantum chaos research.

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Chaos in the quantum world

To observe quantum chaos, the physicists in Innsbruck cool erbium atoms to a few hundred nanokelvin and load them in an optical dipole trap composed of laser beams. They then influence the scattering behavior of the particles by using a magnetic field. After holding the atoms in the trap for 400 milliseconds, the researchers record the atom number remaining in the trap. Thus, the scientists are able to determine at which magnetic field two atoms are coupled to form a weakly-bound molecule. At this magnetic field, so-called Fano-Feshbach resonances emerge. After varying the magnetic field in each experimental cycle and repeating the experiment 14,000 times, the physicists identified 200 resonances. "We were fascinated by how many resonances of this type we found. This is unprecedented in the physics of ultracold quantum gases," says Francesca Ferlaino's team member Albert Frisch. To explain the high density of resonances, the researchers used statistical methods. By using Wigner's random matrix theory the scientists are able to show that different molecular levels are coupled. This has also been confirmed by computer simulations conducted by Svetlana Kotochigova's research group at Temple University in Philadelphia, Pennsylvania, USA. "The particular properties of erbium cause a highly complex coupling behavior between the particles, which can be described as chaotic," explains Ferlaino. Erbium is relatively heavy and highly magnetic, which leads to anisotropic interaction between atoms. "The electron shell of these atoms do not resemble spherical shells but are highly deformed," explains Albert Frisch. "Therefore, the type of interaction between two erbium atoms is significantly different from other quantum gases that have been investigated so far."

Studying chaos experimentally

In contrast to everyday speech, chaos does not mean disorder for the physicists but rather a well-ordered system that, due to its complexity, shows random behavior. Ferlaino is excited about their breakthrough: "We have created an experiment that provides a controlled environment to study chaotic processes. We cannot characterize the behavior of single atoms in our experiment. However, by using statistical methods, we can describe the behavior of all particles." She compares the method with sociology, which studies the behavior of a bigger community of people, whereas psychology describes the relations between individuals. This work also provides new inroads to the investigation of ultracold gases and, thus, ultracold chemistry." Ferlaino is convinced: "Our work represents a turning point in the world of ultracold gases."
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The experiment and statistical analysis were carried out at the Institute for Experimental Physics at the University of Innsbruck. Theoretical support was provided by John L. Bohn from the Joint Institute for Laboratory Astrophysics in Boulder, Colorado, USA and the team of Svetlana Kotochigova at Temple University in Philadelphia, Pennsylvania, USA. The Austrian researchers are supported by the Austrian Science Fund FWF and the European Research Council (ERC).

Publication: Quantum Chaos in Ultracold Collisions of Erbium. Frisch A, Mark M, Aikawa K, and Ferlaino F, Bohn JL, Makrides C, Petrov A, and Kotochigova S. Nature 2014 DOI: 10.1038/nature13137 [arXiv:1312.1972v1, http://arxiv.org/abs/1312.1972v1]

News Release Source :  Quantum chaos in ultracold gas discovered

Saturday, March 29, 2014

Physicists discover 'quantum droplet' in semiconductor

JILA physicists discover 'quantum droplet' in semiconductor


BOULDER, Colo -- JILA physicists used an ultrafast laser and help from German theorists to discover a new semiconductor quasiparticle—a handful of smaller particles that briefly condense into a liquid-like droplet.

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Quasiparticles are composites of smaller particles that can be created inside solid materials and act together in a predictable way. A simple example is the exciton, a pairing, due to electrostatic forces, of an electron and a so-called "hole," a place in the material's energy structure where an electron could be, but isn't.

The new quasiparticle, described in the Feb. 27, 2014, issue of Nature* and featured on the journal's cover, is a microscopic complex of electrons and holes in a new, unpaired arrangement. The researchers call this a "quantum droplet" because it has quantum characteristics such as well-ordered energy levels, but also has some of the characteristics of a liquid. It can have ripples, for example. It differs from a familiar liquid like water because the quantum droplet has a finite size, beyond which the association between electrons and holes disappears.

Although its lifetime is only a fleeting 25 picoseconds (trillionths of a second), thequantum droplet is stable enough for research on how light interacts with specialized forms of matter.

"Electron-hole droplets are known in semiconductors, but they usually contain thousands to millions of electrons and holes," says JILA physicist Steven Cundiff, who studies the properties of cutting-edge lasers and what they reveal about matter. "Here we are talking about droplets with around five electrons and five holes.

"Regarding practical benefits, nobody is going to build a quantum droplet widget. But this does have indirect benefits in terms of improving our understanding of how electrons interact in various situations, including in optoelectronic devices."

The JILA team created the new quasiparticle by exciting a gallium-arsenide semiconductor with an ultrafast red laser emitting about 100 million pulses per second. The pulses initially form excitons, which are known to travel around in semiconductors. As laser pulse intensity increases, more electron-hole pairs are created, with quantum droplets developing when the exciton density reaches a certain level. At that point, the pairing disappears and a few electrons take up positions relative to a given hole. The negatively charged electrons and positively charged holes create a neutral droplet. The droplets are like bubbles held together briefly by pressure from the surrounding plasma.

JILA's experimental data on energy levels of individual droplet rings agreed with theoretical calculations by co-authors at the University of Marburg in Germany. JILA researchers found they could tap into each energy level by tailoring the quantum properties of the laser pulses to match the particle correlations within the droplets. The droplets seem stable enough for future systematic studies on interactions between light and highly correlated states of matter. In addition, quasiparticles, in general, can have exotic properties not found in their constituent parts, and thus, can play a role in controlling the behavior of larger systems and devices.
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JILA is a joint institute of the National Institute of Standards and Technology (NIST) and University of Colorado Boulder. Cundiff is a NIST physicist. The JILA research is supported by the National Science Foundation, NIST and the Alexander von Humboldt Foundation.

* A.E. Almand-Hunter, H. Li, S.T. Cundiff, M. Mootz, M. Kira and S.W. Koch. Quantum droplets of electrons and holes. Nature. Feb. 27, 2014.

News Release Source :   JILA physicists discover 'quantum droplet' in semiconductor

Helical electron and nuclear spin order in quantum wires

Helical electron and nuclear spin order in quantum wires


Physicists at the University of Basel have observed a spontaneous magnetic order of electron and nuclear spins in a quantum wire at temperatures of 0.1 kelvin. In the past, this was possible only at much lower temperatures, typically in the microkelvin range. The coupling of nuclei and electrons creates a new state of matter whereby a nuclear spin order arises at a much higher temperature. The results are consistent with a theoretical model developed in Basel a few years ago, as reported by the researchers in the scientific journal Physical Review Letters.

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The researchers, led by Professor Dominik Zumbühl from the University of Basel's Department of Physics, used quantum wires made from the semiconductor gallium arsenide. These are one-dimensional structures in which the electrons can move in only one spatial direction.

At temperatures above 10 kelvin, the quantum wires exhibited universal, quantized conductance, suggesting that the electron spins were not ordered. However, when the researchers used liquid helium to cool the wires to a temperature below 100 millikelvin (0.1 kelvin), the electronic measurements showed a drop in conductance by a factor of two, which would suggest a collective orientation of the electron spin. This state also remained constant when the researchers cooled the sample to even lower temperatures, down to 10 millikelvin.

Electron-nuclear spin coupling

The results are exceptional because this is the first time that nuclear spin order has been measured at temperatures as high as 0.1 kelvin. Previously, spontaneous nuclear spin order was observed only at much lower temperatures, typically below 1 microkelvin; i.e. five orders of magnitude lower in temperature.

The reason why nuclear spin order is possible already at 0.1 kelvin is that the nuclei of the gallium and arsenic atoms in these quantum wires couple to the electrons, which themselves act back on the nuclear spins, which again interact with the electrons, and so on. This feedback mechanism strongly amplifies the interaction between the magnetic moments, thus creating the combined nuclear and electron spin magnetism. This order is further stabilized by the fact that the electrons in such quantum wires have strong mutual interactions, bumping into each other like railcars on a single track.

Helical electron and nuclear spin order

Interestingly, in the ordered state, the spins of the electrons and nuclei do not all point in the same direction. Instead, they take the form of a helix rotating along the quantum wire. This helical arrangement is predicted by a theoretical model described by Professor Daniel Loss and collaborators at the University of Basel in 2009. According to this model, the conductance drops by a factor of two in the presence of a nuclear spin helix. All other existing theories are incompatible with the data from this experiment.

A step closer to the development of quantum computers

The results of the experiment are important for fundamental research, but are also interesting for the development of quantum computers based on electron spin as a unit of information (proposed by Daniel Loss and David P. DiVincenzo in 1997). In order for electron spins to be used for computation, they must be kept stable for a long period. However, the difficulty of controlling nuclear spins presents a major source of error for the stability of electron spins.

The work of the Basel physicists opens up new avenues for mitigating these disruptive nuclear spin fluctuations: with the nuclear spin order achieved in the experiment, it may be possible to generate much more stable units of information in the quantum wires.

In addition, the nuclear spins can be controlled with electronic fields, which was not previously possible. By applying a voltage, the electrons are expelled from the semiconductor, which dissolves the electron-nucleus coupling and the helical order.

International research partnership

The work was conducted by an international team led by Professor Dominik Zumbühl from the University of Basel's Department of Physics; the team received support in the measurements from Harvard University (Professor Amir Yacoby). The nanowires originated from Princeton University (Loren N. Pfeiffer and Ken West).

The research was co-funded by the European Research Council, the Swiss National Science Foundation, the Basel Center for Quantum Computing and Quantum Coherence (Basel QC2 Center), the Swiss Nanoscience Institute and the NCCR Quantum Science & Technology (QSIT).
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Scientists use 'voting' and 'penalties' to overcome errors in quantum optimization

Scientists use 'voting' and 'penalties' to overcome errors in quantum optimization


Study demonstrates that when the D-Wave quantum processor is led astray by noise, error correction can ensure that it functions as intended

Seeking a solution to decoherence—the "noise" that prevents quantum processors from functioning properly—scientists at USC have developed a strategy of linking quantum bits together into voting blocks, a strategy that significantly boosts their accuracy.

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In a paper published today in Nature Communications, the team found that their method results in at least a five-fold increase in the probability of reaching the correct answer when the processor solves the largest problems tested by the researcher, involving hundreds of qubits.

The team, led by Daniel Lidar—director of the USC-Lockheed Martin Quantum Computing Center at the USC Viterbi School of Engineering—ran their tests on the 512-quantum-bit D-Wave Two processor. The D-Wave Two is among the first commercially available quantum processors, a device so advanced that there are only two in use outside the Canadian company where they were built: The first one went to USC and Lockheed Martin, and the second to NASA and Google.

"We have demonstrated that our quantum annealing correction strategy significantly improves the success probability of the D-Wave Two processor on the benchmark problem of antiferromagnetic chains, and are planning to next use it on computationally hard problems," Lidar said. His team includes graduate student Kristen Pudenz and postdoctoral fellow Tameem Albash.

Lidar added that all quantum information processors are expected to be highly susceptible to decoherence, so that error correction is viewed as an essential and inescapable part of quantum computing.

Quantum processors encode data in qubits, which have the capability of representing the two digits of one and zero at the same time – as opposed to traditional bits, which can encode distinctly either a one or a zero. This property, called superposition, along with the ability of quantum states to "interfere" (cancel or reinforce each other like waves in a pond) and "tunnel" through energy barriers, is what may one day allow quantum processors ultimately perform optimization calculations much faster than traditional processors.

Decoherence knocks qubits out of superposition, forcing them to behave as traditional bits, and robbing them of their edge over traditional processors.

Pudenz, Albash and Lidar developed and tested a strategy of grouping three qubits together into larger blocks of encoded qubits that can be decoded by a "majority vote." This way, if decoherence affects one of the qubits and causes it to "flip" to the incorrect value, the other two qubits in the block ensure that the data is still correctly encoded and can be correctly decoded by out-voting the errant qubit.

These voting blocks of qubits are then magnetically tied to a fourth qubit in such a way that if any one "flips" then all four must flip. In effect, it makes the whole block of four so massive that it's difficult for one lonely qubit acting under the influence of decoherence to throw a wrench in the works.
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This research was funded by the Army Research Office, the Lockheed Martin Corporation, and the National Science Foundation.

Read the study at: http://www.nature.com/ncomms/2014/140206/ncomms4243/full/ncomms4243.html

News Release Source :  Scientists use 'voting' and 'penalties' to overcome errors in quantum optimization

Thursday, March 27, 2014

Integration brings quantum computer a step closer

Integration brings quantum computer a step closer


An international research group led by the University of Bristol has made an important advance towards a quantum computer by shrinking down key components and integrating them onto a silicon microchip.

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Scientists and engineers from an international collaboration led by Dr Mark Thompson from the University of Bristol have, for the first time, generated and manipulated single particles of light (photons) on a silicon chip – a major step forward in the race to build a quantum computer.

Quantum computers and quantum technologies in general are widely anticipated as the next major technology advancement, and are poised to replace conventional information and computing devices in applications ranging from ultra-secure communications and high-precision sensing to immensely powerful computers. While many of the components for a quantum computer already exist, for a quantum computer to be realised, these components need to be integrated onto a single chip.

Featuring today on the front cover of Nature Photonics, this latest advancement is one of the important pieces in the jigsaw needed in order to realise a quantum computer. While previous attempts have required external light sources to generate the photons, this new chip integrates components that can generate photons inside the chip. "We were surprised by how well the integrated sources performed together," admits Joshua Silverstone, lead author of the paper. "They produced high-quality identical photons in a reproducible way, confirming that we could one day manufacture a silicon chip with hundreds of similar sources on it, all working together. This could eventually lead to an optical quantum computer capable of perform enormously complex calculations."

"Single-photon detectors, sources and circuits have all been developed separately in silicon but putting them all together and integrating them on a chip is a huge challenge," explains group leader Mark Thompson. "Our device is the most functionally complex photonic quantum circuit to date, and was fabricated by Toshiba using exactly the same manufacturing techniques used to make conventional electronic devices."

The group, which, includes researchers from Toshiba Corporation (Japan), Stanford University (US), University of Glasgow (UK) and TU Delft (The Netherlands), now plans to integrate the remaining necessary components onto a chip, and show that large-scale quantum devices using photons are possible.

"Our group has been making steady progress towards a functioning quantum computer over the last five years," said Thompson. "We hope to have a photon-based device which can rival modern computing hardware for highly-specialised tasks within the next couple of years."

Much of the work towards this goal will be carried out at Bristol's new Centre for Doctoral Training in Quantum Engineering, which will train a new generation of engineers, scientists and entrepreneurs to harness the power of quantum mechanics using state-of-the-art engineering technique to make real world and useful quantum enhanced devices. This innovative centre bridges the gaps between physics, engineering, mathematics and computer science, working closely with chemists and biologists while interacting strongly with industry.
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Wednesday, March 26, 2014

Quantum Physics Could Make Secure, Single-use Computer Memories Possible

Quantum physics could make secure, single-use computer memories possible


Computer security systems may one day get a boost from quantum physics, as a result of recent research from the National Institute of Standards and Technology (NIST). Computer scientist Yi-Kai Liu has devised away to make a security device that has proved notoriously difficult to build—a "one-shot" memory unit, whose contents can be read only a single time.

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The research, which Liu is presenting at this week's Innovations in Theoretical Computer Science conference,* shows in theory how the laws of quantum physics could allow for the construction of such memory devices. One-shot memories would have a wide range of possible applications such as protecting the transfer of large sums of money electronically. A one-shot memory might contain two authorization codes: one that credits the recipient's bank account and one that credits the sender's bank account, in case the transfer is canceled. Crucially, the memory could only be read once, so only one of the codes can be retrieved, and hence, only one of the two actions can be performed—not both.

"When an adversary has physical control of a device—such as a stolen cell phone—software defenses alone aren't enough; we need to use tamper-resistant hardware to provide security," Liu says. "Moreover, to protect critical systems, we don't want to rely too much on complex defenses that might still get hacked. It's better if we can rely on fundamental laws of nature, which are unassailable."

Unfortunately, there is no fundamental solution to the problem of building tamper-resistant chips, at least not using classical physics alone. So scientists have tried involving quantum mechanics as well, because information that is encoded into a quantum system behaves differently from a classical system.

Liu is exploring one approach, which stores data using quantum bits, or "qubits," which use quantum properties such as magnetic spin to represent digital information. Using a technique called "conjugate coding, "two secret messages—such as separate authorization codes—can be encoded into the same string of qubits, so that a user can retrieve either one of the two messages. But as the qubits can only be read once, the user cannot retrieve both.

The risk in this approach stems from a more subtle quantum phenomenon: "entanglement," where two particles can affect each other even when separated by great distances. If an adversary is able to use entanglement, he can retrieve both messages at once, breaking the security of the scheme.

However, Liu has observed that in certain kinds of physical systems, it is very difficult to create and use entanglement, and shows in his paper that this obstacle turns out to be an advantage: Liu presents a mathematical proof that if an adversary is unable to use entanglement in his attack, that adversary will never be able to retrieve both messages from the qubits. Hence, if the right physical systems are used, the conjugate coding method is secure after all.

"It's fascinating how entanglement—and the lack thereof—is the key to making this work," Liu says. "From a practical point of view, these quantum devices would be more expensive to fabricate, but they would provide a higher level of security. Right now, this is still basic research. But there's been a lot of progress in this area, so I'm optimistic that this will lead to useful technologies in the real world."
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*Y-K Liu. "Building one-time memories from isolated qubits." Paper presented at the ITCS 20-14 Innovations in Theoretical Computer Science meeting, Princeton University, Jan. 11-14, 2014. More info athttp://itcs2014.wordpress.com/program/.

News Release Source : Quantum physics could make secure, single-use computer memories possible

Monday, March 24, 2014

Possibility of Cloning Quantum Data from The Past

LSU researcher shows possibility of cloning quantum information from the past


Popular television shows such as "Doctor Who" have brought the idea of time travel into the vernacular of popular culture. But problem of time travel is even more complicated than one might think. LSU's Mark Wilde has shown that it would theoretically be possible for time travelers to copy quantum data from the past.

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It all started when David Deutsch, a pioneer of quantum computing and a physicist at Oxford, came up with a simplified model of time travel to deal with the paradoxes that would occur if one could travel back in time. For example, would it be possible to travel back in time to kill one's grandfather? In the Grandfather paradox, a time traveler faces the problem that if he kills his grandfather back in time, then he himself is never born, and consequently is unable to travel through time to kill his grandfather, and so on. Some theorists have used this paradox to argue that it is actually impossible to change the past.

"The question is, how would you have existed in the first place to go back in time and kill your grandfather?" said Mark Wilde, an LSU assistant professor with a joint appointment in the Department of Physics and Astronomy and with the Center for Computation and Technology, or CCT.

Deutsch solved the Grandfather paradox originally using a slight change to quantum theory, proposing that you could change the past as long as you did so in a self-consistent manner.

"Meaning that, if you kill your grandfather, you do it with only probability one-half," Wilde said. "Then, he's dead with probability one-half, and you are not born with probability one-half, but the opposite is a fair chance. You could have existed with probability one-half to go back and kill your grandfather."

But the Grandfather paradox is not the only complication with time travel. Another problem is the no-cloning theorem, or the no "subatomic Xerox-machine" theorem, known since 1982. This theorem, which is related to the fact that one cannot copy quantum data at will, is a consequence of Heisenberg's famous Uncertainty Principle, by which one can measure either the position of a particle or its momentum, but not both with unlimited accuracy. According to the Uncertainty Principle, it is thus impossible to have a subatomic Xerox-machine that would take one particle and spit out two particles with the same position and momentum – because then you would know too much about both particles at once.

"We can always look at a paper, and then copy the words on it. That's what we call copying classical data," Wilde said. "But you can't arbitrarily copy quantum data, unless it takes the special form of classical data. This no-cloning theorem is a fundamental part of quantum mechanics – it helps us reason how to process quantum data. If you can't copy data, then you have to think of everything in a very different way."

But what if a Deutschian closed timelike curve did allow for copying of quantum data to many different points in space? According to Wilde, Deutsch suggested in his late 20th century paper that it should be possible to violate the fundamental no-cloning theorem of quantum mechanics. Now, Wilde and collaborators at the University of Southern California and the Autonomous University of Barcelona have advanced Deutsch's 1991 work with a recent paper inPhysical Review Letters (DOI: 10.1103/PhysRevLett.111.190401). The new approach allows for a particle, or a time traveler, to make multiple loops back in time – something like Bruce Willis' travels in the Hollywood film "Looper."

"That is, at certain locations in spacetime, there are wormholes such that, if you jump in, you'll emerge at some point in the past," Wilde said. "To the best of our knowledge, these time loops are not ruled out by the laws of physics. But there are strange consequences for quantum information processing if their behavior is dictated by Deutsch's model."

A single looping path back in time, a time spiral of sorts, behaving according to Deutsch's model, for example, would have to allow for a particle entering the loop to remain the same each time it passed through a particular point in time. In other words, the particle would need to maintain self-consistency as it looped back in time.

"In some sense, this already allows for copying of the particle's data at many different points in space," Wilde said, "because you are sending the particle back many times. It's like you have multiple versions of the particle available at the same time. You can then attempt to read out more copies of the particle, but the thing is, if you try to do so as the particle loops back in time, then you change the past."

To be consistent with Deutsch's model, which holds that you can only change the past as long as you can do it in a self-consistent manner, Wilde and colleagues had to come up with a solution that would allow for a looping curve back in time, and copying of quantum data based on a time traveling particle, without disturbing the past.

"That was the major breakthrough, to figure out what could happen at the beginning of this time loop to enable us to effectively read out many copies of the data without disturbing the past," Wilde said. "It just worked."

However, there is still some controversy over interpretations of the new approach, Wilde said. In one instance, the new approach may actually point to problems in Deutsch's original closed timelike curve model.

"If quantum mechanics gets modified in such a way that we've never observed should happen, it may be evidence that we should question Deutsch's model," Wilde said. "We really believe that quantum mechanics is true, at this point. And most people believe in a principle called Unitarity in quantum mechanics. But with our new model, we've shown that you can essentially violate something that is a direct consequence of Unitarity. To me, this is an indication that something weird is going on with Deutsch's model. However, there might be some way of modifying the model in such a way that we don't violate the no-cloning theorem."

Other researchers argue that Wilde's approach wouldn't actually allow for copying quantum data from an unknown particle state entering the time loop because nature would already "know" what the particle looked like, as it had traveled back in time many times before.

But whether or not the no-cloning theorem can truly be violated as Wilde's new approach suggests, the consequences of being able to copy quantum data from the past are significant. Systems for secure Internet communications, for example, will likely soon rely on quantum security protocols that could be broken or "hacked" if Wilde's looping time travel methods were correct.

"If an adversary, if a malicious person, were to have access to these time loops, then they could break the security of quantum key distribution," Wilde said. "That's one way of interpreting it. But it's a very strong practical implication because the big push of quantum communication is this secure way of communicating. We believe that this is the strongest form of encryption that is out there because it's based on physical principles."

Today, when you log into your Gmail or Facebook, your password and information encryption is not based on physical principles of quantum mechanical security, but rather on the computational assumption that it is very difficult for "hackers" to factor mathematical products of prime numbers, for example. But physicists and computer scientists are working on securing critical and sensitive communications using the principles of quantum mechanics. Such encryption is believed to be unbreakable – that is, as long as hackers don't have access to Wilde's looping closed timelike curves.

"This ability to copy quantum information freely would turn quantum theory into an effectively classical theory in which, for example, classical data thought to be secured by quantum cryptography would no longer be safe," Wilde said. "It seems like there should be a revision to Deutsch's model which would simultaneously resolve the various time travel paradoxes but not lead to such striking consequences for quantum information processing. However, no one yet has offered a model that meets these two requirements. This is the subject of open research."
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Scientists Achieves Secure Cloud Computing with Quantum Computers

International team of scientists achieves secure “cloud” computing with quantum computers


A team of scientists, including CIFAR Junior Fellow Anne Broadbent, have demonstrated that “blind quantum computing” is now possible. An experiment published in the latest issue of Science, showed that quantum computation could occur and keep the input, data processing and output unknown to the quantum computer.

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With the use of light particles, the scientists were able to send data to a quantum computer, have the computer solve the computation and then send the data back, all without revealing the information being transmitted. This proved that quantum computers could perform calculations required of a user remotely, but have no means to find out what it is actually doing. Everything would remain perfectly encrypted - a level of security not achievable in the current world of classical computing.

Quantum computers are considered the next generation in high performance computing, able to solve complicated problems deemed impossible for classical computers. In present day, large scale data storage and data processing is handled through remote centres of supercomputers. Everything is performed in a “cloud”, but the challenge to date has been ensuring that a users’ data stays private.

These findings are an exciting breakthrough for scientists hoping to achieve secure and global quantum computing.

Read more

News Source : International team of scientists achieves secure “cloud” computing with quantum computers

Quantum physics secures new cryptography scheme

Quantum physics secures new cryptography scheme


The way we secure digital transactions could soon change. An international team has demonstrated a form of quantum cryptography that can protect people doing business with others they may not know or trust – a situation encountered often on the internet and in everyday life, for example at a bank's ATM.

[caption id="attachment_223" align="aligncenter" width="400"]Quantum physics secures new cryptography scheme www.quantumcomputingtechnologyaustralia.com-025 Quantum physics secures new cryptography scheme[/caption]

"Having quantum cryptography to hand is a realistic prospect, I think. I expect that quantum technologies will gradually become integrated with existing devices such as smartphones, allowing us to do things like identify ourselves securely or generate encryption keys," says Stephanie Wehner, a Principal Investigator at the Centre for Quantum Technologies (CQT) at the National University of Singapore, and co-author on the paper.

In cryptography, the problem of providing a secure way for two mutually distrustful parties to interact is known as 'two-party secure computation'. The new work, published in Nature Communications, describes the implementation using quantum technology of an important building block for such schemes.

CQT theorists Wehner and Nelly Ng teamed up with researchers at the Institute for Quantum Computing (IQC) at the University of Waterloo, Canada, for the demonstration.

"Research partnerships such as this one between IQC and CQT are critical in moving the field forward," says Raymond Laflamme, Executive Director at the Institute for Quantum Computing. "The infrastructure that we've built here at IQC is enabling exciting progress on quantum technologies."

"CQT and IQC are two of the world's largest, leading research centres in quantum technologies. Great things can happen when we combine our powers," says Artur Ekert, Director of CQT.

The experiments performed at IQC deployed quantum-entangled photons in such a way that one party, dubbed Alice, could share information with a second party, dubbed Bob, while meeting stringent restrictions. Specifically, Alice has two sets of information. Bob requests access to one or the other, and Alice must be able to send it to him without knowing which set he's asked for. Bob must also learn nothing about the unrequested set. This is a protocol known as 1-2 random oblivious transfer (ROT).

ROT is a starting point for more complicated schemes that have applications, for example, in secure identification. "Oblivious transfer is a basic building block that you can stack together, like lego, to make something more fantastic," says Wehner.

Today, taking money out of an ATM requires that you put in a card and type in your PIN. You trust the bank's machine with your personal data. But what if you don't trust the machine? You might instead type your PIN into your trusted phone, then let your phone do secure quantum identification with the ATM (see artist's impression). Ultimately, the aim is to implement a scheme that can check if your account number and PIN matches the bank's records without either you or the bank having to disclose the login details to each other.

Unlike protocols for ROT that use only classical physics, the security of the quantum protocol cannot be broken by computational power. Even if the attacker had a quantum computer, the protocol would remain secure.

Its security depends only on Alice and Bob not being able to store much quantum information for long. This is a reasonable physical assumption, given today's best quantum memories are able to store information for minutes at most. Moreover, any improvements in memory can be matched by changes in the protocol: a bigger storage device simply means more signals have to be sent in order to achieve security. (The idea of 'noisy storage' securing quantum cryptography was developed by Wehner in earlier papers.)

To start the ROT protocol, Alice creates pairs of entangled photons. She measures one of each pair and sends the other to Bob to measure. Bob chooses which photons he wants to learn about, dividing his data accordingly without revealing his picks to Alice. Both then wait for a length of time chosen such that any attempt to store quantum information about the photons is likely to fail. To complete the oblivious transfer, Alice then tells Bob which measurements she made, and they both process their data in set ways that ensure the result is correct and secure within a pre-agreed margin of error.

In the demonstration performed at IQC, Alice and Bob achieved a random oblivious transfer of 1,366 bits. The whole process took about three minutes.

The experiment adapted devices built to do a more standard form of quantum cryptography known as quantum key distribution (QKD), a scheme that generates random numbers for scrambling communication. Devices for QKD are already commercially available, and miniaturised versions of this experiment are in principle possible using integrated optics. In the future, people might carry hand-held quantum devices that can perform this kind of feat.

"We did the experiment with big and bulky optics taking metres of space, but you can well imagine this technology being shrunk down to sit happily next to classical processing circuits on a small little microchip. The field of integrated quantum optics has been progressing in leaps and bounds, and most of the key pieces required to implement ROT have already been successfully demonstrated in integrated setups a few millimetres in size," says Chris Erven, who performed the experiments at IQC as a PhD student under the supervision of Raymond Laflamme and Gregor Weihs. Weihs is now at the University of Innsbruck, Austria. Erven is now a postdoctoral fellow at the University of Bristol, UK.

 
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Reference:

"An Experimental Implementation of Oblivious Transfer in the Noisy Storage Model", Nature Communications DOI:10.1038/ncomms4418 (2014)

http://www.nature.com/naturecommunications

A preprint is available at http://arxiv.org/abs/1308.5098

Researcher contacts:

Stephanie Wehner
Principal Investigator and Associate Professor, Centre for Quantum Technologies
National University of Singapore
Tel: +65 6601 1478
Email: wehner@comp.nus.edu.sg

Chris Erven
Then: PhD Student, Institute for Quantum Computing, University of Waterloo, Canada
Now: Postdoctoral Fellow, University of Bristol, UK
Tel: +44 (0)117 331 7340
Email: chris.erven@bristol.ac.uk

Raymond Laflamme
Executive Director, Institute for Quantum Computing
University of Waterloo, Canada
Tel: +1 519-888-4422
Email: Laflamme@iqc.uwaterloo.ca

News Release Source :  Quantum physics secures new cryptography scheme

Monday, March 10, 2014

Diamond Defect Boosts Quantum Technology

Diamond defect boosts quantum technology


Washington, D.C.—New research shows that a remarkable defect in synthetic diamond produced by chemical vapor deposition allows researchers to measure, witness, and potentially manipulate electrons in a manner that could lead to new "quantum technology" for information processing. The study is published in the January 31, 2014, issue of Physical Review Letters.

[caption id="attachment_216" align="aligncenter" width="500"]Diamond Boosts Quantum Technology www.quantumcomputingtechnologyaustralia.com-024 Diamond Boosts Quantum Technology[/caption]

Normal computers process bits, the fundamental ones and zeros, one at a time. But in quantum computing, a "qubit" can be a one or a zero at the same time. This duplicitous state can allow multitasking at an astounding rate, which could exponentially increase the computing capacity of a tiny, tiny machine.

An "NV-" center can be created within a diamond's scaffold-like structure by replacing a missing carbon atom with a nitrogen atom (N)that has trapped an electron making the center negatively charged. Scientists can monitor the center's behavior and thereby provide a window for understanding how electrons respond to different conditions. The center has the potential to serve as a qubit in future quantum computers.

Electrons occupy different orbits around their atom and, by analogy, spin like the Earth. For the first time, Struzhkin and his team, led by Marcus Doherty of the Australian National University, observed what happens to electrons in these NV- centers under high-pressure and normal temperatures. Coauthor of the study, Viktor Struzhkin at the Carnegie Institution for Science, explained: "Our technique offers a powerful new tool for analyzing and manipulating electrons to advance our understanding of high-pressure superconductivity, as well as magnetic and electrical properties."

Struzhkin and team subjected single-crystal diamonds to pressures up to 600,000 times atmospheric pressure at sea level (60 gigapascals, GPa) in a diamond anvil cell and observed how electron spin and motion were affected. They optically excited the NV- centers with light and scanned microwave frequencies in a process called optically detected magnetic resonance to determine any changes. The NV- center is very sensitive to magnetic fields, electrical fields, and stress.

Until now, researchers thought that the orbits of the electrons that contribute to the defect's electronic structure and spin dynamics were localized to the area immediately surrounding the vacancy. Doherty explained: "Our team found instead that the electrons also orbit more distant atoms and that the span of their orbits contract with increasing pressure."

In addition to overturning previous beliefs about the electron orbits, the researchers found a sensitive means to measure pressure. This method can detect changes in pressure of about 10 atmospheres in one second, even up to pressures of 500,000 atmospheres (50 GPa).

"This work demonstrates that defects in diamond have great potential as quantum sensors of high pressure phenomena and, conversely, that high pressure can be employed to study the quantum phenomena of the defects," remarked Doherty.

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This work was supported by BES/DOE, DOE-NNSA, the Australian Research Council Discovery Project, Centre of Excellence for Quantum Computation and Communications Technology, and the Alexander von Humboldt Foundation.

The Carnegie Institution for Science is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

News Release Source :  Diamond defect boosts quantum technology