1) Highway on-ramp control
Ding-wei Huang
Physical Review E (Print issue: April 2002)
The study of traffic flow has received a lot of attention from physicists in recent years. One area of interest concerns how congestion occurs. On-ramps of highway systems are quite susceptible to congestion but this study shows that it does not occur randomly but is induced by specific qualities of the traffic flow. Certain types of fluctuations in the inflow trigger traffic jams. Within a wide range of flows, both free flow and congestion are stable. Thus, appropriate control mechanisms can be employed to suppress the traffic jams. Techniques such as closing an on-ramp for 30 second periods at times could prevent the formation of jams on the highway itself.
Journal article: http://link.aps.org/abstract/PRE/v65/e046103
2) Osmium is less compressible than diamond
H. Cynn, J. E. Klepeis, C. Yoo, and D. Young
Physical Review Letters (Print issue: April 1, 2002)
Compressibility is an important physical property of a material. Previously, the record for lowest compressibility (which is correlated with mechanical hardness) was held by covalently bonded diamond. New studies of the metal osmium break that record to give a bulk modulus (the inverse of compressibility) of 462 GPa compared with 443 GPa for diamond. The authors comment that it is intriguing that a light, covalently bonded element such as diamond and a heavy, metallic element, osmium, with very different boding, can both have low compressibility. The study may help researchers discover superhard materials.
Journal article: http://link.aps.org/abstract/PRL/v88/e135701
3) Terabit transmission rates
Inside Science News Service
Researchers from Agere Systems have set a record for data transmission rates having sent 3.2 terabits per second over a 1000 km fiber optic line using dense wavelength division multiplexing (DWDM).
Article: http://www.aip.org/isns/reports/2002/039.html
4) Entropy gives DNA a shove
S. W. P. Turner, M. Cabodi, and H. G. Craighead
Physical Review Focus/Physical Review Letters (Print issue: March 25, 2002)
The folding properties of DNA depend on its entropy, a measure of the disorder or randomness of configurations. Experiments have shown that the tendency to move to higher entropy states (more disordered configurations) causes previously unraveled molecules to retangle. By exploiting this property, DNA fragments could be sorted by size, just as is done for DNA fingerprinting.
Physical Review Focus: http://focus.aps.org/v9/st15.html
Journal article: http://link.aps.org/abstract/PRL/v88/e128103
5) Quantum computing without qubits
Richard B. Kassman, Gennady P. Berman, Vladimir I. Tsifrinovich, and Gustavo V. Lopez
arXiv preprint server
The basic unit of computation is the bit and every bit of information is represented by a physical subsystem such as a magnetic domain or collection of electric charge. In quantum computing, the fundamental unit of computation is the qubit. Proposals for quantum computing generally involve creating a set of physical subsystems that represent individual qubits and making them interact to perform computations. This proposal consists of many strongly interacting particles in which there are no physically identifiable qubits. Instead, effective qubits exist as multi-particle states within the amalgam. The authors show theoretically and via simulations, how this type of system can be made to perform quantum computations.
Preprint: http://www.arxiv.org/abs/quant-ph/0203059
6) "Quantum" search with classical optics
N. Bhattacharya, H. B. van Linden van den Heuvell, and R. J. C. Spreeuw
Physical Review Letters (Print issue: April 1, 2002)
One of the most controversial questions in quantum computing asks just how “quantum” is a particular computer. An early quantum algorithm is Grover’s quantum search, which finds an item in an unsorted database much faster than a classical search could. An experimental implementation is performed using classical light waves and is just as efficient as it would be quantum mechanically. This shows that quantum entanglement is not necessary for the algorithm or its efficiency. The limitation on this technique is that it will not work for databases as large as could be handled using quantum mechanics. Previous experiments in this field have either searched only four database items or only been able to perform a single query on the database.
Journal article: http://link.aps.org/abstract/PRL/v88/e137901
7) Quantum computer games
Jiangfeng Du, Hui Li, Xiaodong Xu, Mingjun Shi, Jihui Wu, Xianyi Zhou, Rongdian Han
Physical Review Letters (Print issue: April 1, 2002)
A new application of quantum information is to game theory, a branch of applied mathematics that concerns decision-making and conflict between different agents. In this paper, a quantum game is implemented on a nuclear magnetic resonance (NMR) quantum computer. The game in question is the prisoner’s dilemma, in which two isolated prisoners are offered incentives to turn in their collaborator in exchange for a lesser sentence. For each prisoner, the option of turning in their collaborator results in a better option than keeping quiet. However, a better option is available for both prisoners if neither turn in the other, hence the dilemma. In a quantum version of this game, the best strategy changes and the dilemma disappears.
Journal article: http://link.aps.org/abstract/PRL/v88/e137902