2002 Articles
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PHYSICSWEB DEC 02 |
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boost for organic LEDs PHYSICSWEB DEC 02 Researchers have produced an organic light-emitting diode (LED) that is about 25 times more efficient than the best quantum-dot LEDs to date. The structure contains a single layer of cadmium-selenium quantum dots sandwiched between two organic thin films. Seth Coe and colleagues at the Massachusetts Institute of Technology believe that their approach could be used to fabricate other hybrid organic-inorganic devices (S Coe et al. 2002 Nature 420 800). CLICK ON ARTICLE TITLE FOR MORE INFORMATION |
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Caesium condensate makes its debut PHYSICSWEB DEC 02 |
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World record for silicon light-emission PHYSICSWEB NOV 02 |
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Electronic devices based on single molecules PHYSICSWEB NOV 02 |
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In the matter of J Hendrik Schön PHYSICSWEB NOV 02 |
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Bosons help to beat the Fermi pressure PHYSICSWEB NOV 02 |
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| Molecules power nanoscale computers PHYSICSWEB OCT02 |
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| Quantum key travels record distance PHYSICSWEB OCT02 |
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PHYSICSWEB OCT02 |
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| Atom lithography sees the light PHYSICSWEB OCT02 |
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| Quantum logic: to be, or NOT to be? PHYSICSWEB OCT02 |
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Electron
pairs behave like bosons
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Nano-boost
for data storage
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Defects
combine to make perfect devices Faulty components are usually rejected in the manufacture of computers and other high-tech devices. However, Damien Challet and Neil Johnson of Oxford University say that this need not be the case. They have used statistical physics to show that the errors from defective electronic components or other imperfect objects can be combined to create near perfect devices (D Challet and N Johnson 2002 Phys. Rev. Lett. 89 028701). Click on title above for further information. |
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Magnets
open the gate to nanoscale logic
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Single
photons to soak up data A new technique that measures the orbital - rather than the spin - angular momentum of single photons could lead to the development of super-efficient quantum communication systems. Previously, physicists had only been able to measure this quantity for many photons in a beam, or detect a certain value of it for single photons. But the set-up devised by Miles Padgett of the University of Glasgow and colleagues should be able to reveal any orbital angular momentum state of a single photon (J Leach et al 2002 Phys. Rev. Lett. 88 257901). Click on title above for further information. |
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Magnetic
spins to store quantum information
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Laser
lithography makes cheaper chips
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New
phase shift for neutrons A
surprising prediction about the quantum properties of neutron beams made
in the late 1980s has been confirmed in experiments. More than a decade
ago Jean Levy-Leblond and Daniel Greenberger had independently predicted
that a neutron beam passing through a slit would experience a phase shift
in its direction of motion. Now Helmut Rauch and co-workers at the Atomic
Institute of the Austrian Universities in Vienna and the Institut Laue-Langevin
(ILL) in Grenoble have measured this confinement induced phase shift in
an experiment (H Rauch et al 2002 Nature 417 630). |
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Quantum
dots count microwave photons A versatile single-photon
detector that works at microwave frequencies has been developed by physicists
in Japan. Created by Oleg Astafiev and colleagues of the University of
Tokyo, the detector does not use the magnetic fields that made earlier
devices unsuitable for many of their desired applications. According to
Astafiev, many areas of research have been hindered in the past by a lack
of suitable photon counters (O Astafiev et al 2002 Appl. Phys. Lett. 80
4250). |
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Tiny
transistors nudge the nanoscale Physicists in the US have
taken a significant step towards nanometre-scale electronics by creating
the first transistor made from a single atom. A similar device based on
a single divanadium molecule - which consists of two vanadium atoms -
has also been built by a second US team. The researchers are optimistic
that the transistors will prove to be rich sources of exotic electronic
effects, and that their achievements will stimulate research that could
lead to the development of practical nanoelectronics systems. |
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Tantalizing
evidence for molecular condensation Researchers
in the US claim to have created a molecular Bose-Einstein condensate,
a state of matter in which many molecules co-exist in the same quantum
state. Elizabeth Donley and colleagues at the JILA laboratory in Boulder
say that they have observed coherent oscillations between atoms and molecules
in a sample of rubidium-85. The discovery could have important applications
in molecular physics, chemistry and quantum computing (E Donley et al
2002 Nature 417 529). |
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'Nanotorus'
nets giant magnetic moment
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Condensates
get longer lives A new generation of 'atom lasers' could be around the corner following the creation of the first perpetual Bose-Einstein condensate by researchers in the US. Wolfgang Ketterle and colleagues at the Massachusetts Institute of Technology say that their achievement solves the biggest problem in the development of a continuous-wave atom laser. Physicists could probe fundamental properties of matter and light with such devices, which could also be used for applications including atom lithography and atomic clocks (A Chikkatur et al 2002 Science to appear). Click on title above for further information. |
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Spintronics
gets serious
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Molecules
take electronics for a spin
They take advantage of a hitherto unexploited property of electric currents, called spin, to make molecular devices that operate under new rules. This fledgling form of electronics, called spintronics, could lead to computers that don't forget anything when their power is turned off, and perhaps even to that ultra-powerful device, the quantum computer. Click on title above for further information. |
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Call
for Papers: European Physical
Journal
"Quantum fluctuations and coherence in optical and atomic structures" to appear in a special issue of the European Physical Journal D early next year. Your contribution would be most welcome. For further information, please visit http://www.edpsciences.com/docinfos/EPJD/call.pdf. |
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Quantum
computers get real
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Photons
get the quantum cloning treatment Near-perfect copies of single photons have been made in the lab for the first time. Quantum systems cannot be cloned - or duplicated - perfectly, but the development of quantum cryptography and computing relies on a knowledge of exactly how well they can be copied. Antia Lamas-Linares and co-workers at the University of Oxford sent a photon into a crystal where it stimulated the emission of another photon with almost the same properties, confirming theoretical predictions (A Lamas-Linares et al 2002 Science to appear). |
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'DNA
computer' cracks code A 'DNA computer' has been used for the first time to find the only correct answer from over a million possible solutions to a computational problem. Leonard Adleman of the University of Southern California in the US and colleagues used different strands of DNA to represent the 20 variables in their problem, which could be the most complex task ever solved without a conventional computer. The researchers believe that the complexity of the structure of biological molecules could allow DNA computers to outperform their electronic counterparts in future (R Braich et al 2002 Science to appear). Click on title above for editorial. |
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Losses
and games for quantum computers Physicists believe that quantum computers are capable of outperforming classical computers for certain tasks. But now researchers at the University of Amsterdam have shown that classical laser pulses can perform one of these tasks - a database search - just as quickly as the quantum approach. Meanwhile, researchers at the University of Science and Technology of China have shown that a riddle known as the prisoner's dilemma has an unusual outcome when it is treated as a quantum problem. Click on title above for editorial. |
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Quantum
dots break new ground
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Cold
atoms carry light pulses Physicists have demonstrated for the first time that light pulses trapped in atomic gases can be transported in space, changed in frequency and reversed in time. Marlan Scully of Texas A&M University in the US and colleagues believe that the ability to transport and modify light pulses in this way could be exploited for quantum information storage (A Zibrov et al 2002 Phys. Rev. Lett. 88 103601-1). Click on title above for editorial. |
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Quantum
interference and cryptographic keys: novel physics and advancing technologies
(QUICK) This special issue of The European Physical Journal D was organised in conjunction with the conference "Quantum interference and cryptographic keys: novel physics and advancing technologies (QUICK)", that took place in the Institut d'Etudes Scientifiques de Cargese from April 7th to 13th, 2001. This conference was organised at the initiative of the European Quantum Communication and Cryptography projects QuComm, S4P, QuiCoV, EQUIS and EQCSPOT, in the framework of the European Union IST/FET/QIPC program. Click on title above for editorial. |
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Holograms
help build 3D nanostructures A new method of building complex nanoscale structures has been demonstrated by Dieter Meschede of the University of Bonn in Germany and colleagues. The team created a three-dimensional interference pattern by shining a laser into a 'holographic crystal', and used the pattern as a stencil to position atoms from an atom laser. This technique could be used to construct ultra-small photonic crystals, and could pave the way for all-optical circuits (M Mützel et al 2002 Phys. Rev. Lett. 88 083601-1). Click on title above for full article. |
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Quantum
wires probe electrons |
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Nuclei
put a new spin on quantum computing |
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Crystal
catches light pulses Pulses of light have been slowed down and stopped in a solid for the first time. Alexey Turukhin of the Massachusetts Institute of Technology in the US and colleagues used an yttrium-based crystal to slow light pulses to just 45 metres per second, and then to trap and release them. Previously, these effects had only been seen in gases, which are more difficult to control. A solid should be easier to develop into real applications, such as high-density information storage for quantum computing (A Turukhin et al 2002 Phys. Rev. Lett. 88 023602). For full text click title above. |
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New
look for Bose condensates For full text click title above. |
A
new twist on a classic experiment could show that pairs of electrons behave
as bosons, despite the fact that single electrons are fermions. Peter
Samuelsson and Markus Büttiker of the University of Geneva in Switzerland
propose an update of the Hanbury Brown-Twiss experiment that would probe
the pairs of electrons found in many superconductors. The pioneering experiment
originally illustrated a fundamental difference in the quantum behaviour
of bosons and fermions (P Samuelsson and M Büttiker 2002 Phys. Rev. Lett.
89 046601). 
A
nanometre-scale logic gate that works at room temperature and is made
entirely from metal has been developed by UK physicists. According to
Russell Cowburn's team at the University of Durham, the ferromagnetic
NOT gate is a "completely new class of device" that could be made even
smaller. The researchers have also created a 13-bit shift register by
linking the devices together, and believe it should be possible to make
a full set of logic gates using their technique (D Allwood et al 2002
Science 296 2003).
Magnets
could be the latest materials to be used in quantum information systems
following the discovery of unusual spin effects in a fluorine-based compound.
Tom Rosenbaum of the University of Chicago in the US and colleagues found
that the spins of clusters of atoms in the magnetic compound became aligned
- or coherent - when a magnetic field was applied, in contrast with the
behaviour of similar materials. This coherence persisted for up to ten
seconds, and the researchers say that the clusters could have information
'imprinted' on them (S Ghosh et al 2002 Science 296 2195). 
Silicon
chips could be made more quickly and cheaply using a new technique developed
by physicists in the US. Stephen Chou and colleagues at Princeton University
have successfully imprinted patterns onto silicon using quartz moulds
instead of the usual combination of lithography and etching. With a resolution
of just 10 nm and an 'imprint time' of 250 ns, the new process could revolutionize
the semiconductor industry - and keep 'Moore's Law' on track for another
25 years (S Chou et al 2002 Nature 417 835).
Carbon
nanotubes bent into rings are the latest nanostructures to display surprising
properties, according to new calculations. Shi-Yu Wu of the University
of Louisville and colleagues found that the magnetic moments of some metallic
`nanotori' were thousands of times stronger when the rings had certain
`magic' radii. The researchers believe that such unexpected properties
could be explained by the unusual behaviour of the electrons when they
circulate in the ring-shaped structures (L Liu et al 2002 Phys. Rev. Lett.
88 217206). 
Spintronic
devices, which harness the spin of the electron as well as its charge,
could be a step closer following recent experiments on `spin valves'.
Physicists in the US have changed the spins of electrons travelling through
a single molecule for the first time, proving that spintronics is compatible
with the emerging field of molecular electronics. Meanwhile, a group in
the Netherlands has reversed the sign of the output voltage of a device
by changing the spins of the electrons flowing through it. 
Researchers
eager to use individual molecules as the components of ultra-small electronic
circuits and computers have put a new spin on their ambitious goal.
A
quantum computer has successfully factorized a number for the first time.
Bose-Einstein
condensates (BECs) have opened yet another promising avenue of experimental
research. This time, the road leads to an opportunity to study quantum
phase transitions in a very clean and controlled manner. Specifically,
researchers from the Max Planck Institute for Quantum Optics in Garching,
Germany and the University of Munich have shown that they can take a dilute
of gas of cold atoms from a superfluid to an insulator - and back again
- simply by varying the intensity of a laser beam... 
The
sequence of photons emitted by artificial atoms can now be controlled
by optical pumping.