Formation of Journal on Quantum Information Processing

The quantum afterburner
Physics Web - February 2002

Quantum mechanics could be used to improve the efficiency of heat engines, according to Marlan Scully of Texas A&M University in the US. Scully has calculated that exhaust energy from an engine could be used to power a laser. This would improve engine performance beyond that of the ideal Otto cycle without violating the laws of thermodynamics (M Scully 2002 Phys. Rev. Lett. 88 050602).

Click on title above for full article.

Semiconductor laser makes broadband debut
Physics Web - February 2002

The first broadband laser based on semiconductors has been developed by physicists in the US. In contrast to existing devices - which emit pulses of light - the laser emits a continuous beam of infrared radiation over a two-micrometre wavelength range. Claire Gmachl and colleagues at Bell Labs believe their laser - which they plan to modify to emit visible light - could be used for gas sensing, metrology and optical communications (C Gmachl et al 2002 Nature 415 883).

Click on title above for full article.

Torino Workshop - October 2001 - VIDEO FOOTAGE

The 2nd European QIPC Workshop held in Torino, Italy in October last year was a huge success. Over twenty-five speakers from Europe and Australia presented talks on QIPC Implementation, Algorithms & Theory and Communications. Over 150 QIPC researchers attended the event where they had the chance to socialise and discuss issues with other research groups from all over Europe.

Please take a look at the video link above to see the highlights of the event - this will take approximately 15 seconds to load.

During this event there featured a Hot Topics section. Each selected topic was videoed:

• A ringing squbit - Rabi oscillations in a superconducting qubit
• Photon Guns
• Bose-Einstein condensation in a magnetic chip trap
• Macroscopic spin entanglement
• SQUID Flux State Qubit: Stroboscopic single shot read-out
• Vacuum-stimulated photon bursts from a coupled atom-cavity system

The 3rd European QIPC Workshop will be held this year in September 2002 at the Trinity College, Dublin, Ireland.

Single photon machine gears up
PhysicsWeb - December 2001

The first practical electrically driven single-photon generator could play a key role in the emerging technologies of quantum cryptography and quantum computing. Andrew Shields of Toshiba Research Europe in Cambridge and colleagues at Toshiba and the University of Cambridge added a layer of ‘quantum dots’ to a conventional light-emitting diode to create their device, which could also be used for extremely sensitive optical experiments (Zhiliang Yuan et al 2001 Science to appear). continued ...

A marriage made for the nanoworld
PhysicsWeb - December 2001

Near-field optics and nonlinear optics team up to probe the nanoworld of quantum dots.

Light is beautiful. It can probe matter in a multitude of ways, but there are limitations when we try to use it to investigate the revolution in nanotechnology that is currently taking place. The first problem with light in the nanometre domain is diffraction. Light cannot be focused to a point smaller than half its wavelength - this is the famous Rayleigh criterion of optical resolution. The second problem is out-of-focus light. In essence, light that passes through a lens illuminates the regions before and after the focal point, as well as the focal spot itself.

An approach known as spectral confinement may be capable of restricting light to within a few nanometres along certain directions. Spectral confinement occurs when we consider how the electrons and atoms in a molecular or a solid-state system interact with the large electric field that is produced by a laser.

The combination of near-field optics (with its spatial restrictions on light) and nonlinear optics (with its spectral confinement of light), is a marriage made in heaven. And in the quest to probe optical properties at the resolutions associated with the nanoworld, the combined technique is the star on the horizon.

Now Jeffrey Guest and co-workers at the University of Michigan and the Naval Research Laboratory in Washington have taken a step on this road by employing both near-field optics and nonlinear optics to probe the nanoworld of a quantum-dot system (J Guest et al. 2001 Science 293 2224). In the December issue of Physics World, Aaron Lewis of The Hebrew University of Jerusalem, Israel, shows how the new approach opens a window on the analysis of nanoscale semiconductor systems.

Nobel Prize for Bose condensates
PhysicsWeb - 5th October 2001

The 100th Nobel Prize for Physics been awarded to the researchers who created the first Bose-Einstein condensates - the so-called fifth state of matter - in the laboratory. Eric Cornell of JILA and National Institute of Standards and Technology in Boulder, Colorado, Wolfgang Ketterle of the Massachusetts Institute of Technology, and Carl Wieman of JILA and the University of Colorado, share the 2001 prize for "the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates".

The Universal Quantum Hall Effect?
Science - 26th October 2001 - Vol 294, No 5543

One of the pursuits of theoretical physics is the unification of the three pillars of modern physics--quantum mechanics, special relativity, and general relativity. Unification of the first two principles has been done successfully with the development of relativistic quantum field theory, but unifying gravity and quantum mechanics has remained elusive. An ideal solution would be finding a quantum-mechanical wave function, or Hamiltonian, of a system from which relativity emerges. Zhang and Hu (p. 823) have taken the quantum Hall effect, a many-body effect involving electrons confined to a two-dimensional (2D) plane in a magnetic field, and generalized the mathematical description to a 4D space plus time. Upon examination of the low-energy states on the surface of this space, they find that certain elements of electromagnetism and gravity emerge from the mathematics. By no means a grand unification theory, the work does suggest that the symmetry properties of other systems may provide a route for further study.

Magnetic field-induced quantum criticality
Science - 12th October 2001 - Vol 294, No 5541

Quantum criticality, where a phase transition can be induced in the limit of zero temperature by application of external parameter (such as pressure, electric fields, or chemical substitution) has proven fruitful ground for experimental and theoretical investigation of correlated systems. However, the parameters used to tune these systems can create problems of their own, such as restricting the dimensionality of the system or introducing disorder that may mask some of the more interesting properties. Grigera et al. (p. 329; see the Perspective by Aeppli and Soh) present magneto- transport data on the ruthenate Sr3Ru3O7 that reveal the existence of a well-defined, magnetically tuned quantum critical point. A closer examination of the temperature dependence of this transition reveals behavior that is not readily explained by the current understanding of quantum criticality.

First nanotube circuits get logical
PhysicsWeb - 5th October 2001

The ever-shrinking world of electronics just got smaller following the first demonstration of digital logic circuits made from carbon nanotubes. Cees Dekker and team at Delft University of Technology in the Netherlands used different combinations of 'nanotube transistors' to create several devices, including a voltage inverter and a NOR gate. As conventional silicon microelectronics approaches its fundamental size limit, Dekker and colleagues believe that their devices - which work at room temperature - are an important step towards nano-electronics.

Condensate control could lead to 'atom circuits'
PhysicsWeb - 4th October 2001

German physicists have shown for the first time that Bose-Einstein condensates can be created and manipulated using so-called atom chips. The achievement by Jakob Reichel and colleagues at Ludwig-Maximilians University in Munich could form the basis of integrated 'atom circuits' based on the motion of atoms rather than electrons. A lithographic technique was used to create the effect, which could bring devices such as quantum computers a step closer (W Hansel et al 2001 Nature 413 498).

Purdue builds quantum-computing semiconductor chip
EETIMES.com
By R. Colin Johnson - 1st October 2001

Quantum-dot techniques have produced the first examples of quantum computing in a semiconductor at Purdue University. Using electron-beam lithography to deposit small metal islands over a gallium arsenide (GaAs) heterostucture interface, scientists created isolated regions that trap only a few electrons. More important, two of the dots were placed close enough for the team to observe quantum-spin interactions, a discovery that might lead to semiconductor-based quantum computers.

"The special thing about what we have been able to accomplish is to put two quantum dots together and observe an effect that is related both to the spin physics of the system and the interaction, or coupling, between the dots. That has never been done before," said lead researcher Albert Chang, a Purdue professor and a 12-year veteran of AT&T Bell Laboratories' Microstructure Physics Research Department. "This is field-opening work for implementing qubits [quantum bits] for quantum computation in a semiconductor-based system".

Excitons take charge of optoelectronics
Physics Web - 27th September 2001

Physicists have shown for the first time that 'excitons' - the particles that emit light in semiconductors - can be controlled with an electric field, if they have a negative charge. The ability to move excitons - also known as electron-hole pairs - could open up new ways to control light emission in optoelectronic devices, according to Andrew Shields of Toshiba Research Europe in Cambridge and colleagues.

When light falls on a semiconductor, electrons are excited from the 'valence band' - where they are tightly bound to their parent atom - into the 'conduction band', where they can move and contribute to current flow. Each electron leaves a 'positive hole' in the valence band, and the electron stays close to this hole in a bound system called an exciton. The exciton can move through the semiconductor, but it is not influenced by electric fields because it has no net charge.

But an exciton can have an overall negative charge if it attracts an extra electron to form a 'trion'. To encourage trions to form, Shields and colleagues added extra electrons, in the form of silicon 'donor' atoms, to a gallium arsenide structure. When they applied a voltage across the structure, they found that the trions drifted several micrometres towards the positive terminal. This overturns the long-held idea that trions are held still - or 'pinned' - by the attraction of positive ions in the semiconductors...

Entanglement leaps to larger scales
Physics Web - 27th September 2001

Two macroscopic objects have been 'entangled' for the first time. Eugene Polzik and colleagues at the University of Aarhus in Denmark entangled two samples of caesium atoms, each containing about 1012 atoms, for half a millisecond - a long time by quantum standards. This demonstration could form the basis of new forms of 'quantum teleportation' and quantum computers.

Entanglement is a feature of quantum mechanics that allows particles to share a much closer relationship than classical physics permits. A measurement on one part of an entangled system reveals the properties of the other part, even if they are physically separated...

The Quandary of Quantum Information
Science - 14th September 2001, Vol 293, No 5537
Charles Seife

The past few years have seen a flurry of advances in quantum computing, as physicists figure out how to use quantum information to perform feats that are impossible in the classical world. Yet even as theorists crank out quantum software, they have been astonished to discover that a phenomenon long considered essential for quantum computing--entanglement--appears to be dispensable after all. That leaves them wondering just which exotic properties of the quantum realm combine to give quantum computers their incredible potential.

Protecting Quantum Memory
Science - 14th September 2001, Vol 293, No 5537

A major problem in quantum information processing (see the Viewpoint by Gershenfeld) is the coupling between the quantum system and its environment that leads to decoherence and effective loss of memory of the system. Although quantum error correction codes and the engineering of decoherence- free subspaces (which protect the system under special circumstances) can help, a formulation for protecting against arbitrary noise is not yet available. Viola et al. (p. 2059) present an experimental realization of a noiseless subsystem, a generalization of the decoherence-free subspace implementation but without its strong symmetry constraints. The results indicate that it may not be necessary to protect the whole system (as in the decoherence-free subspace approach), but that a general and more efficient technique may be used instead.

Dissipating Decoherence
Science - 24th August, Vol 293, No 5534

Exploiting macroscopic quantum coherence effects of superconducting systems is thought to be one promising route for developing qubits, the logical devices from which quantum computers will be built. Within this framework, the Josephson junction is one of the key components that requires further study, especially the decoherence dynamics of the junction. Han et al. (p. 1457) present time-resolved measurements of the decoherence dynamics of the quantum two-level system that reveal a temperature-dependent decay of the system from the ground state and the first excited state. They also observed a prominent double-exponential decay for intermediate temperatures. The measured decoherence time (>11 microseconds) shows sufficient promise for device applications.

Quantum entanglement gets a laser-like lift
PhysicsWeb - 29th August 2001

Lasers have been used to amplify light for many years, but physicists have now achieved a similar feat with pairs of 'entangled' photons for the first time. The phenomenon could lead to a reliable method for creating such pairs, which could be the basis of future quantum computers and encryption techniques. Antia Lamas-Linares and co-workers at the University of Oxford, UK, exploited quantum effects to boost the number of entangled photons created when an ultraviolet laser passes through a crystal (A Lamas-Linares et al 2001 Nature 412 887).

For more detail, visit http://physicsweb.org/article/news/5/8/20

Big move toward ultra-tiny computers
InformationWeek - 13th August 2001
by Jason Levitt

The practical implementation of sub-atomic quantum computers is a significant step closer, as a result of research led by scientists at the Depart-ment of Energy's Pacific Northwest National Labora-tory in Richland, Wash. They've devised semiconductor material that has superior magnetic properties at room temperature. Until now, impractical cooling techniques would be required to maintain the magnetic properties of semiconductor material. A team headed by Scott Chambers, a senior chief scientist at the lab, created the substance using a method called molecular beam epitaxy. It generates individual beams of atoms, in this case titanium, oxygen, and cobalt, in a highly controlled vacuum and directs them onto a crystalline surface of strontium titanate, where the atoms condense and form a crystalline film with dimensions on the nanoscale.

Quantum computers store data as a series of quantum states, such as the spin directions of an electron. By controlling the spin within this semiconductor material, researchers hope to greatly increase computational speeds and data storage over conventional silicon-based computer technologies. In quantum computers, particles can hold more than one state at a time, so they theoretically could quickly crunch numbers and make lightning-fast database searches possible.

http://informationweek.com/

Toward a light-wave generator
Science - 17th August 2001, Volume 293

Mixing light waves of different frequencies is a routine technique for synthesizing waveforms of arbitrary shape and spectral composition. For applications in coherent quantum control, ultrafast optical pulses over a range of wavelengths may be required. Shelton et al. (p. 1286; see the Perspective by Brown et al.), building on recent advances involving phase- locking of femtosecond optical pulses, generation of a comb of optical frequencies, and precision measurement of optical frequencies, now show that two waveforms can be coherently stitched together from separate femtosecond lasers to form a coherent pulse train.

Counting photons in a flash
PhysicsWeb - 8th August 2001

A single-photon counter based on a superconductor promises to be thousands of times more sensitive - and much faster - than conventional semiconductor detectors. The device could spot faulty components in computers, and may even be used for communication between Earth and Mars in the future, according to Roman Sobolewski of the University of Rochester and colleagues.

Url: http://PhysicsWeb.org/article/news/5/8/5

Shocking behaviour in Condensates
Science - 27th July 2001, Volume 293, Issue 5530

Although defects are often unwanted, their controlled introduction can provide useful signatures or probes of a medium. The ability to introduce localized defects into Bose-Einstein condensates (BECs) would be an extremely useful tool to probe the properties of such macroscopic quantum systems and superfluids. Combining their slow-light technique with electromagnetic-induced tranparency, Dutton et al. (p. 663) report the formation of localized defects in a BEC and the response of the BEC to the defect. Small-scale, large-amplitude sound wave collapse in the BEC results in the breakdown of the superfluidity by the formation of topological defects such as solitons and the nucleation of vortices. The results present a superfluid analog to classical shock waves.

Single-atom delivery on demand
Science - 13th July 2001, Volume 293, Issue 5528

The manipulation of single-quantum objects is a key requirement for the engineering of microscopic quantum systems. Applications such as single-atom micromasers (microwave lasers), triggered single-photon sources, or deterministic entanglement of atoms all require the ability to deliver single atoms on demand to a desired location. The trapping and manipulation of atoms as neutral species is more challenging than for charged ions because of the weak interaction of neutral species with electromagnetic fields. Kuhr et al. (p. 278) have overcome these difficulties by combining magneto-optical trapping and optical-trapping techniques. They demonstrate the precision transport of single neutral cesium atoms over distances of 1 centimeter and the ejection of single atoms into free flight.

Lighting the way to a Quantum Computer
Science - 29th June 2001, Volume 292, Issue 5526
Robert F Service

Researchers have taken a small step toward creating a machine that can carry out in seconds calculations that would take eons on even the most sophisticated supercomputer. Below, they report using a trio of vanishingly brief laser pulses to tweak bits of quantum data in as little as 100 quadrillionths of a second. The group hasn't demonstrated any computation power yet, but experts call the work a very important milestone in quantum computing.

Ultrafast Manipulation of Electron Spin Coherence
J.A.Gupta, R.Knobel, N.Samarth,D.D.Awschalom

A technique is developed with the potential for coherent all-optical control over electron spins in semiconductors on femtosecond time scales. The experiments show that optical "tipping" pulses can enact substantial rotations of electron spins through a mechanism dependent on the optical Stark effect. These rotations were measured as changes in the amplitude of spin precession after optical excitation in a transverse magnetic field and approach /2 radians. A prototype sequence of two tipping pulses indicates that the rotation is reversible, a result that establishes the coherent nature of the tipping process.

To whom correspondence should be addressed. E-mail: awsch@physics.ucsb.edu

Electrons dance in the Spotlight
Science - 29th June 2001, Volume 292, Issue 5526

Application of a magnetic field polarizes the spin of an electron in the direction of the magnetic field. The net moment of an electronic ensemble can rotate in response to a varying magnetic field, and methods such as nuclear magnetic resonance can take advantage of this effect to probe the electronic environment of many materials. In semiconductors, however, the lifetime of conduction electrons is on the time scale of the shortest magnetic field pulses and so other techniques are required. Gupta et al. (p. 2458; see the cover and the news story by Service) show that an optical tipping pulse can induce an effective magnetic field that causes the precessional dynamics of the magnetic moment to be altered in a controlled and reversible manner. The femtosecond length scales of these optical pulses are so short that electrons could be probed thousands of times in their coherent lifetimes, thus opening applications in quantum computing.

Atoms one by one

"Subpoissonian loading of single atoms in a microscopic dipole trap"
Nature 411, 1024-1027 - 28th June 2001

One possible route to quantum information processing is to use cold, stored atoms as qubits. But to do this requires the ability to manipulate and store atoms in a controlled fashion, and precisely one at a time. In their paper, Nicolas Schlosser and colleagues describe an optical dipole trap so small that only one atom can fit. Thanks to a diffraction-limited focusing lens, the width of the laser beam at the focal spot of their trap is less than 1 µm. The presence of an atom in the dipole trap is detected using fluorescence photons induced by optical molasses beams. Counting of these photons shows that the dipole trap never holds more than one atom at a time. Two neighbouring traps, each one holding only one atom, have also been achieved by the same group (see picture).

For more information see : "News & Views" in Nature 411, 1010 (28 june 2001). The web site : http://www.iota.u-psud.fr/~grangier/Quantum_optics.html

No mere anarchy
Science - 13th July 2001, Volume 293, Issue 5528

Quantum tunneling through a potential barrier is a well-understood phenonmenon that, for example, explains hydrogen tunneling in chemical reactions. Add a time dependence, however, and things become more murky, as Habib explains in his Perspective. He highlights the report by Steck et al., who have gone one step further and have studied quantum dynamics in a classically chaotic system. Their observations provide experimental proof of chaos-assisted tunneling.
The author is in the Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
E-mail: habib@lanl.gov

Single atoms on demand
PhysicsWorld - June 2001

Quantum computers - in which data is stored as the quantum state of an atomic particle - could in principle outperform conventional computers. But it is difficult to control the single atoms that are necessary for the technique.

Stefan Kuhr and colleagues at the University of Bonn in Germany may have overcome this barrier with the development of an 'atom trap' that can manipulate single atoms with sub-micron precision and can deliver them on demand (click on title to see full document).

High speed satellite secrecy a step closer
New Scientist - July 2001
Will Knight

Hopes of sending vast amounts of absolutely secure data via satellites has taken step forward, with research showing that a superconducting material could perform quantum cryptography at previously impossible speeds.

The key advance, by researchers at the Mitre Corporation in Massachusetts, Rochester University in New York and the US Airforce research laboratory, is to show that the superconducting material niobium-nitrate can count vast numbers of photons very rapidly. Photons can be used to represent binary ones and zeros for communications. It is already possible to send photons in a quantum state though fibre optics or through air using a pulse laser.

But current laser systems can only send information at roughly 10 kilobits per second. By using the niobium-nitrate superconductor cooled to below 9 Kelvin, Gerald Gilbert, director of Quantum Information Science Group at the Mitre Corporation, estimates that transmission speeds of one gigabit per second may be achievable.

Gilbert is optimistic, saying that a prototype, ground-based communication system could be built within 18 months. "We believe there is no fundamental obstacle and expect the engineering problems should be resolvable," he toldNew Scientist. But he admits, "It's one thing to confirm in a laboratory that this can be done, but another to put buttons on it."

One way street
Cryptography can be unbreakable if sender and recipient can exchange genuinely random ciphers, or keys, before communication. Current cryptography often relies on an observable key exchange mechanism and is consequently very difficult to break but not impossible.

Typically a mathematical device, known as a one way function, provides a way to disguise messages in a form that would be impractical to attack without colossal computer power.

Quantum cryptography promises to deliver absolute security to conventional communications methods. This is because any effort to intercept a quantum channel of communications would destroy its quantum nature and automatically lead to detection. This could be used to distribute unbreakable one-time keys or send secure messages themselves. One gigabit per second of data transfer would generate a satellite communications link comparable to current telecommunications.

"The ultimate application would be real time encryption of images," says Gilbert. "And we're most likely to see a military application in the short term."

Long way up
The scheme is certainly ambitious. Others have shown that free space quantum cryptography can be achieved over hundreds of metres but never as far as a satellite. "It would have a hell of a long way to go," says Jonathan Jones of Oxford University's Centre for Quantum Computation. "And it would be interesting to see if you could launch a complete quantum system in one piece."

Gilbert presented the results of the research on high-speed photon detection at the Quantum Applications Symposium, in Michigan, US.

Quantum solutions to difficult problems
Science - Volume 292, Number 5516, Issue of 20 April 2001

There are certain problems, for example, factoring or searching for the shortest route connecting several points (the traveling salesman problem), that classically appear to grow exponentially in computational time with the number of digits (in factoring) or points that can be tried (in a search). So far, classical algorithms for solving the wide range of related "NP-complete" problems that could yield answers in polynomial time have remained elusive. From simulations, Farhi et al. (p. 472; see the news story by Anderson ) show that quantum computers may be more effective at solving such problems. At least for the number of qubits they could simulate on their classical computer, they show that the adiabatic evolution of their quantum computer would yield a result to some examples of NP-complete problems in polynomial time.

Worldwide QIPC group listing now available at QUIPROCONE!

Following requests at the Seefeld Review this year, the Australian listing of QIPC groups and individuals has now been added to the 'Sites of Interest' section within the QUIPROCONE website. Please take a look.

Linearly polarised light from out-of-shape particles
Science - 15th June 2001

Spherical semiconductor quantum dots can emit light at optical wavelengths when charge carriers in the dot recombine, and by changing the size of the particle, the emission strength and wavelength can be tuned. This emission is plane polarized, but it would be even more useful in applications such as displays if the emission were linearly polarized. Hu et al. (p. 2060) now show experimentally that elongating CdSe dots even to only an aspect ratio of 2 results in linearly polarized emission.

New Academic Staff Appointments - University of London

New Academic Staff Appointments Lectureships, Reader and Professor

The Department of Physics, Queen Mary, University of London, wishes to maintain its international research excellence by developing major new research themes that provide a natural synergy with existing strengths of the College in medical, biological, materials or IT research.

Applications are invited for up to four academic staff posts. Two will be filled immediately and it is expected to appoint to the others early in the academic year 2001/02.

The Department encourages applications from candidates with outstanding research achievements, appropriate to their career point. One of the first two posts may be at Readership or Professorial level and the successful applicant for this post will be involved in subsequent appointments. Applicants with strong backgrounds in, or wishing to develop, interdisciplinary topics such as the practical implementation of quantum computing, novel functional materials and heterostructures, or properties of biological surfaces and membranes, will be especially welcome.

Salaries, which include London Allowance, will be at the appropriate points within the Lecturer, Reader or Professorial scales.
For information on the department and its current activities please refer to http://www.ph.qmw.ac.uk/.
For an application form and further enquiries, please e-mail phys-recruit@qmw.ac.uk or telephone +44 (0)20 7882 5030, quoting reference Phys1904. Completed applications should be returned to the Head of Department, Prof. P.E. Clegg, Physics Department, Queen Mary, University of London, London E1 4NS.

Getting all entangled up
P G Kwiat et al. 2001 Nature 409 1014

In 1936, in the same paper in which he introduced his famous cat, Erwin Schrödinger drew attention to a feature of quantum mechanics that he called entanglement. Since then entanglement ­ a connection between separated particles that Einstein described as "spooky" ­ has come to be seen as the source of much that is difficult to understand in quantum theory.

In the last decade, however, a more constructive aspect of entanglement has emerged, and it is now seen as a valuable resource that could provide significant improvements in our powers of communication and computing. Now Paul Kwiat and Salvado Barraza-Lopez of the Los Alamos National Laboratory, and André Stefanov and Nicolas Gisin of the University of Geneva, have shown experimentally that entanglement can be manipulated, controlled and even concentrated or "distilled" (P G Kwiat et al. 2001 Nature 409 1014).

Quantum solutions to difficult problems
Science - Volume 292, Number 5516, Issue of 20 April 2001

There are certain problems, for example, factoring or searching for the shortest route connecting several points (the traveling salesman problem), that classically appear to grow exponentially in computational time with the number of digits (in factoring) or points that can be tried (in a search). So far, classical algorithms for solving the wide range of related "NP-complete" problems that could yield answers in polynomial time have remained elusive. From simulations, Farhi et al. (p. 472; see the news story by Anderson ) show that quantum computers may be more effective at solving such problems. At least for the number of qubits they could simulate on their classical computer, they show that the adiabatic evolution of their quantum computer would yield a result to some examples of NP-complete problems in polynomial time.

Souped-up software gets a virtual test
Science - Volume 292, Number 5516, Issue of 20 April 2001
Mark K. Anderson

In theory, quantum computers can outpace conventional ones a billionfold, but how do you test a potential "killer app" for a machine that doesn't yet exist? If you have time, you can run it on machines that do exist. That's how researchers pitted a quantum algorithm against one of the toughest problems in computer science. In preliminary tests, described on page 472 of this issue, the algorithm racked up an encouraging virtual track record that left some scientists hankering for more.

Standing Room Only at the Quantum Scale
Science Magazine, Vol. 291, Issue 5513, 2556-2557, March 30, 2001
K. M. O'Hara and J. E. Thomas

Atoms may be bosons and fermions depending on their isotopic mass, and this determines their behavior at very low temperatures. Bosons form quantum degenerate gases called Bose-Einstein condensates. In their Perspective, O'Hara and Thomas highlight the work by Truscott et al., who have made a degenerate fermionic gas through a method called "sympathetic cooling." Such studies will shed light on many processes from superconductivity to the mechanisms driving neutron stars.

The authors are at the Department of Physics, Duke University, Durham, NC 27706, USA. E-mail: jet@phy.duke.edu

Doing the Bose Nova with Your Main Squeeze
Science Magazine - Vol 291, Issue 5512 - March 23, 2001

After 6 years of study, condensed-matter physicists have found, much to their satisfaction, that the tenuous vapors that make up atomic Bose- Einstein condensates resemble much denser substances known as quantum fluids--including the classic superfluid, liquid helium (see www.sciencexpress.org). In other labs, researchers are putting the materials through some weird contortions: engineering them with quantum properties that might lead to ultraprecise measurements of distance or time (see p. 2386); imploding atomic vapors at will to create a kind of miniature supernova or "Bose nova"; and pumping their atoms so full of internal energy that less uniform substances would be instantly destroyed (see www.sciencexpress.org).

Quantum Mechanics: Electron flow in two dimensions
Nature - 8th March 2001

A recently developed imaging technique has been used to reveal the coherent flow of electron waves confined to two dimensions. In the cover image, a simulation of electrons launched uniformly in all directions from the centre of the image replicates the branched flow observed experimentally in a two-dimensional electron gas. This branched flow results from the electrons riding over dozens of potential energy hills and valleys — an inevitable result of the proximity of charged donor atoms in a layer near the gas. As the energy of the electrons is well above the highest potential the branches do not follow any features in the potential, but rather are an indirect effect of repeated focusing/defocusing events resulting from the hills and valleys.

Quantum Mechanical Actuation of Microelectromechanical Systems by the Casimir Force
Science - Vol 291, Issue 5510 - March 2001

The Casimir force is the attraction between uncharged metallic surfaces as a result of quantum mechanical vacuum fluctuations of the electromagnetic field. We demonstrate the Casimir effect in microelectromechanical systems using a micromachined torsional device. Attraction between a polysilicon plate and a spherical metallic surface results in a torque that rotates the plate about two thin torsional rods. The dependence of the rotation angle on the separation between the surfaces is in agreement with calculations of the Casimir force. Our results show that quantum electrodynamical effects play a significant role in such microelectromechanical systems when the separation between components is in the nanometer range.

Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, USA.
* To whom correspondence should be addressed. E-mail: fc@lucent.com

cont.....

The Quantum Mechanics of Micromechanics
Science magazine - March 2001

In classical mechanics, a vacuum is a pretty dull place, but in quantum mechanics, it's quite busy. Quantum fluctuations of the electromagnetic field give rise to fleeting moments in which virtual photons are created and annihilated. If these events take place in the space between two uncharged plates, they cause a pressure differential that pushes the plates together--the Casimir effect. For large-scale separations, these events have little consequence, but as length scales are reduced, as in the case of microelectromechanical systems now being used as actuators, the effect could be significant. Chan et al. (p. 1941) demonstrate that as separations are reduced to the nanometer scale, quantum fluctuations do indeed play a significant role and must be considered in describing the operation of such microfabricated devices.

Quantum Chromodynamics: Quark Quirk Triggers Nuclear Shrinkage
Science - 9th March 2001, 291 (5510)
Charles Seife

By sticking an exotic type of quark where it doesn't belong, physicists report in the 5 March Physical Review Letters that they have cut a few lithium nuclei down to four-fifths normal size. In the process, the scientists are edging toward a theory that can explain nuclear interactions of all varieties.

Trapped over a Chip

Microchips that control hovering atoms may lead to new quantum computers

Until recently, a typical atom trap has consisted of a temperamental labyrinth of electric coils, custom-built and then fine-tuned and maintained by dedicated graduate students. Now scientists are adapting microchip technology to build robust miniaturized devices to trap and control tiny clouds of chilled atoms. Research groups in the U.S., Austria and Germany have demonstrated atom versions of optical fibers and beam splitters, as well as a magnetic "conveyor belt" for moving atoms around precisely--all on devices that look like crude computer chips. According to Jakob Reichel of the Max Planck Institute for Quantum Optics in Garching, Germany, "these microtraps are a promising tool to get quantum coherent interactions on the atomic scale." And that, he adds, "is the most important ingredient for a quantum computer."

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DERA Scientists achieve worldwide record 1.9km range for free-space secure key exchange using quantum cryptography - PRESS RELEASE

Recent experiments at DERA Malvern have shown that a low light level communication scheme can work out to a range greater than 1.9km. In the system individual photons (fundamental particles of light) are used to encode the data. Photons, being quantum particles, are indivisible and only one person can receive the encoded photon hence providing security. However in any realistic system most photons are lost in transmission and no sensible message can be sent. The Malvern system is not used to send any message but it is used to establish identical random numbers at transmitter and receiver. These large random numbers can then be used as CRYPTOGRAPHIC KEYS for encoding and decoding data on a standard communications link. Hence the technique is popularly known as quantum cryptography.

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New journal 'Quantum Information & Computation (QIC)

A unique, bi-monthly, fast journal in quantum computing and information is scheduled to make its first appearance in July/August 2001.

You are invited to submit your papers to the journal. Original articles, survey articles, reviews, tutorials, perspectives, and correspondence are all welcome. Electronic submissions by email at qic@rinton.com or by web uploading are welcome. On-line peer-review for all the papers is conducted. Accepted papers will be published in print and on-line in a timely fashion. (We hope that the time from submission to publication will normally be within four months.)

We enclose more information on the journal below. For further details, please check http://www.rinton.com

Aims and Scope:
Quantum Information & Computation provides a forum for distribution of information in all areas of quantum information processing. Original articles, survey articles, reviews, tutorials, perspectives, and correspondences are all welcome. Computer science, physics and mathematics are covered. Both theory and experiments are included. Illustrative subjects include quantum algorithms, quantum information theory, quantum complexity theory, quantum cryptology, quantum communication and measurements, proposals and experiments on the implementation of quantum computation, communication, and entanglement in all areas of sciences including ion traps, cavity QED, photons, nuclear magnetic resonance, and solid-state proposals.

Toshiba Research Europe Limited - Job Advert

Semiconductor Quantum Optoelectronics

TREL, the European R&D subsiduary of Toshiba Corporation, is sited on the Cambridge Science Park. Work is carried out in close collaboration with the University of Cambridge and Toshiba's R&D center in Japan, as well as several European universities.

We are presently expanding our research and development of advanced optoelectronic devices based upon semiconductor nanostructures. Recent successes have included a novel technology for detection and generation of single photons. To complement our team, we are looking for research physicists or engineers to invent, fabricate and evaluate novel types of optical semiconductor device, as well as integrate these devices into prototype systems.

Candidates should have (or be about to receive) a PhD in Physics, Electronic Engineering or a related discipline. They should be practically minded, enthusiastic and determined to succeed. Crucially they will have demonstrated the capacity, or have the potential, to be highly innovative. Practical experience in semiconductor devices, RF electronics or fibre optics would be an advantage.

An attractive salary and benefit package will be offered.

CV with the names of three referees, by post or e-mail, to:
Dr A J Shields, Toshiba Research Europe Ltd, Cambridge Research Laboratory 260 Cambridge Science Park Milton Road Cambridge CB4 0WE, UK.
E-mail: andrew.shields@crl.toshiba.co.uk
Closing date for applications: 16 July 2001

Linearly polarised emission from colloidal semiconductor quantum rods
Science, Vol. 292, Issue 5524, 2060-2063, 15th June 2001
Jiangtao Hu, Liang-shi Li, Weidong Yang, Liberato Manna, Lin-wang Wang, A. Paul Alivisatos

Colloidal quantum rods of cadmium selenide (CdSe) exhibit linearly polarized emission. Empirical pseudopotential calculations predict that slightly elongated CdSe nanocrystals have polarized emission along the long axis, unlike spherical dots, which emit plane-polarized light. Single-molecule luminescence spectroscopy measurements on CdSe quantum rods with an aspect ratio between 1 and 30 confirm a sharp transition from nonpolarized to purely linearly polarized emission at an aspect ratio of 2. Linearly polarized luminescent chromophores are highly desirable in a variety of applications.

1 Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720, USA.
2 Materials Science Division.
3 National Energy Research Scientific Computing Center, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.

Geometric manipulation of Trapped Ions for Quantum Computation
Science - Volume 292, Issue 5522, 1st June 2001
L.-M. Duan, J. I. Cirac, and P. Zoller

We propose an experimentally feasible scheme to achieve quantum computation based solely on geometric manipulations of a quantum system. The desired geometric operations are obtained by driving the quantum system to undergo appropriate adiabatic cyclic evolutions. Our implementation of the all-geometric quantum computation is based on laser manipulation of a set of trapped ions. An all-geometric approach, apart from its fundamental interest, offers a possible method for robust quantum computation. Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria.

To whom correspondence should be addressed. E-mail: Luming.Duan@uibk.ac.at

Computation from Geometry
Science - Volume 292, Issue 5522, 1st June 2001
Seth Lloyd

Quantum computation is usually performed through optical or magnetic resonance and does not obviously have anything to do with geometry. But, as Lloyd explains in his Perspective, computation can benefit from geometry. He highlights the report by Duan et al., who have found a way to exploit geometry to perform quantum computations more efficiently through sending quantum bits for walks through potential space.

The author is in the Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
E-mail: slloyd@mit.edu

Sandu Popescu wins Adams Prize 2001

Professor Sandu Popescu, a member of the Hewlett-Packard Company's Basic Research Institute in the Mathematical Sciences (BRIMS), has been awarded the prestigious University of Cambridge Adams Prize for the year 2001 for his contributions to the field of quantum information, specifically for his work on quantum non-locality, which led to demonstrations of quantum teleportation.

Popescu holds a joint appointment as a member of Hewlett-Packard Laboratory's (HP Labs) BRIMS and as Professor of Physics at the University of Bristol.

From 1996 to 1999 he held a joint appointment as a member of BRIMS and as Hewlett-Packard Senior Research Fellow at the Isaac Newton Institute for Mathematical Sciences at Cambridge. Popescu's research has been at the forefront of recent developments which link quantum physics to information and computation, and which shed light on some of the deepest and most mysterious phenomena in physics.

BRIMS is a unique collaboration between HP Labs and the Universities of Bristol and Cambridge to undertake basic research in areas of major technology disruption. Popescu's work, along with that of others at HP Labs and at Bristol and Cambridge, is laying the theoretical foundations from which a new world of quantum computing devices will emerge.

The Adams Prize is named after the mathematician John Couch Adams. It commemorates his discovery of the planet Neptune, through calculation of the discrepancies in the orbit of Uranus. The many distinguished scientists who have won the award include James Clerk Maxwell - physicist, Stephen Hawking - theoretical physicist, Roger Penrose - mathematician & theoretical physicist and the Nobel Laureate Abdus Salam - physicist.

Monitoring electron paths in atoms
Science - May 4 2001, 292 (5518)

When an intense laser field interacts with an atom, the excited electrons driven by the laser field can be pulled from the nucleus, perform some complex orbits, and then be driven back to the nucleus, where they can scatter or recombine. Although it is often possible to calculate quantum- mechanical descriptions of such processes, they often can be difficult to appreciate. Feynman's approach to quantum mechanics, which involves summing over all possible paths, or quantum trajectories, provides a somewhat more intuitive description of the processes involved, but many experiments have been difficult to describe in this fashion because of the shear number of paths involved. Salieres et al. (p. 902; see the news story by Seife) used a polarized laser field to limit the number of possible paths and show that the quantum orbit approach can describe the processes.

Formation of Journal on Quantum Information Processing
entitled "Quantum Information and Computation" - First call for papers

We announce the formation of a journal devoted solely on
quantum information processing.

It will be entitled "Quantum Information and Computation'' (QIC). The first issue is scheduled to appear in July/August 2001. This is the first call for papers. We look forward to receiving your masterpieces.

Aims and Scope:
Quantum Information and Computation is a bi-monthly publication (i.e., six issues per year). It provides a forum for the distribution of information in all areas of quantum information processing. Original articles, survey articles, reviews, tutorials, perspectives and correspondences are all welcome. Computer science, physics and mathematics are covered. Both theory and experiments are included. Illustrative subjects include quantum algorithms, quantum information theory, quantum complexity theory, quantum cryptology, quantum communication and measurements, proposals and experiments on the implementation of quantum information processing in all areas of sciences including trapped atoms, cavity quantum electrodynamics, nuclear magnetic resonance, and condensed matter.

Submissions:
Submission of a paper implies that it has not been published, and is not being considered for publication in another journal. Once a paper is accepted for publication in Quantum Information and Computation, the author is assumed to have transferred the copyright to the publisher. All submitted scientific papers will be acknowledged and peer-reviewed. They will not be returned to the authors. You can submit your papers by any of the following means:

• sending the latex file as attachment of an e-mail to qic@rinton.com (template available at www.rinton.com)
• Web Submission through www.rinton.com
• for a paper posted in xxx.lanl archive, sending a note of submission with the number (i.e. quant-ph/9904091) by e-mail to qic@rinton.com
• sending hard copies of your paper in triplicate to: "Quantum Information and Computation", Rinton Editorial, 565 Edmund Terrace, NJ 07652, USA.

Electronic submissions (i.e., 1-3) are particularly encouraged. After acceptance, authors are strongly encouraged to convert their papers into Rinton's special Latex style. Template available at www.rinton.com. This helps to reduce typesetting errors, turnover time and production cost. Authors who are unwilling or unable to convert their papers to the Rinton Latex style will have the conversion done by the Rinton Press.

Subscription: Subscription information can be found at www.rinton.com

Journal of Modern Optics - Call for Papers

Special Issue on "Technologies for Quantum Communications"
Editors: J. G. Rarity, G. S. Buller and N. Gisin

Following successful special issues of the Journal of Modern Optics on "Quantum Communication (Vol.21, N.12, 1994) and "Physics of Quantum Information" (Vol.47, N.2/3, 2000) papers are solicited for a special issue on the underlying technologies of quantum communications. In recent years the technique of secure key sharing, quantum cryptography, has moved towards system implementation. Various technological advances in detectors, sources and encoding are being actively studied, various new quantum communications schemes have emerged and theoretical studies of security in real scenarios have been carried out.

Papers on all aspects of quantum communication technologies are solicited. Some examples of topics especially suited to this special issue include:

• Quantum cryptography systems (fibre and free space)
• Pair photon and multi-photon experiments
• Novel sources for quantum cryptography (single photons, pair photons etc)
• Advances in single photon detection and acquisition technology
• Novel encoding schemes and protocols
• New applications of quantum cryptography
• Security of quantum key distribution
• Quantum repeaters and quantum error correction.

The deadline for submission is 15th January 2001. It is intended that the issue will be published in July 2001. Papers should be submitted to the Editorial Office of the Journal of Modern Optics: Professor Peter L. Knight Optics Section, The Blackett Laboratory Imperial College, London SW7 2BZ ENGLAND
e-mail: p.knight@ic.ac.uk

The Topsy Turvey World of Quantum Computing
IEEE Spectrum - Feb 2001 - 'Advanced Technology' section - page 42
article by Justin Mullins

'The weirdest parts of physics are now the cutting edge of computing technology'

'Strange ideas can come from ordinary places. this one came from Texas. In 1981 John A Wheeler, the father of the black hold and a theoretical physicist at the University of Texas in Austin, threw a party. The guests were all young physicists with a common interest in the foundations of computing, a topic that Wheeler believed - correctly - would become increasingly important in the years to come......'

In the beginning was THE BIT
New Scientist - 17th February 2001

And after that came the rest of the weird world, says Hans Christian von Baeyer

"Nobody understands quantum mechanics," lamented Richard Feynman. But Anton Zeilinger at the University of Vienna aims to prove him wrong. His research group has demonstrated the futuristic phenomena of quantum teleportation and quantum encryption, and these successes have encouraged Zeilinger to search for the essence of quantum mechanics - the irreducible kernel from which everything else flows. He believes that he has found it. If he is right, all the mysteries of the quantum world will turn out to be inescapable consequences of a single, simple idea.
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Coupling and Entangling of Quantum States in Quantum Dot Molecules
Science magazine - Vol 291 - Jan 2001 - page 45

We demonstrate coupling and entangling of quantum states in a pair of vertically aligned, self-assembled quantum dots by studying the emission of an interacting electron-hole pair (exciton) in a single dot molecule as a function of the separation between the dots. An interaction-induced energy splitting of the exciton is observed that exceeds 30 millielectron volts for a dot layer separation of 4 nanometers. The results are interpreted by mapping the tunneling of a particle in a double dot to the problem of a single spin. The electron-hole complex is shown to be equivalent to entangled states of two interacting spins.

How does the individual fit into the large scheme of things? Evan Harris Walker, physicist, and founder and director of the Walker Cancer Institute, tackles many of these issues in a well written, thought-provoking book.

The mathematics of quantum theory is based on operators rather than numbers. In optics this simple fact allows statistical quantities, such as the fluctuations in the electric field of a light beam, to be smaller than is allowed by classical physics. Experiments that measure these quantities can generally be divided into two types, depending on whether they measure the wave or the particle properties of light. This is in line with the "complementarity principle" of quantum mechanics, which states that the wave and particle aspects of a system cannot be observed at the same time.

Now two teams of researchers in the US have developed new techniques that could launch a raft of new measurements into the quantum-mechanical nature of light. Researchers at the University of California at Santa Barbara have produced a type of photon "machine gun" that fires individual photons (P Micheler et al. 2000 Nature 406 968). Meanwhile, a team from the State University of New York at Stony Brook and the University of Oregon has developed a novel technique that draws together the particle and wave aspects of light (G Foster et al. 2000 Phys. Rev. Lett. 85 3149).

Similarly, they can flow effortlessly through narrow channels and pores that are virtually impermeable to conventional liquids. Superfluids are relatively rare and inaccessible, with only two known examples in liquids: helium-3 and helium-4. Now Peter Toennies and co-workers at the Max Planck Institute of Flow Research in Göttingen and the Russian Academy of Sciences in Moscow have revealed convincing evidence for superfluidity in liquid hydrogen (S Grebenev et al. 2000 Science 289 1532).

A new kind of integrated circuit that steers atoms rather than electrons has been developed by a team of researchers. It consists of a few current-carrying wires etched on a gallium-arsenide substrate. The electrical currents produce a complex magnetic-field pattern that is used to manipulate the motion of cold atoms floating above the chip - an exciting achievement!