A Complexity Measure for Continuous Time Quantum Algorithms

We consider unitary dynamical evolutions on n qubits caused by time dependent pair-interaction Hamiltonians and show that the running time of a parallelized two-qubit gate network simulating the evolution is given by the time integral over the chromatic index of the interaction graph. This defines a complexity measure of continuous and discrete quantum algorithms which are in exact one-to-one correspondence. Furthermore we prove a lower bound on the growth of large-scale entanglement depending on the chromatic index.Comment: 6 pages, Revte

Quantum Simulations on a Quantum Computer

We present a general scheme for performing a simulation of the dynamics of one quantum system using another. This scheme is used to experimentally simulate the dynamics of truncated quantum harmonic and anharmonic oscillators using nuclear magnetic resonance. We believe this to be the first explicit physical realization of such a simulation.Comment: 4 pages, 2 figures (\documentstyle[prl,aps,epsfig,amscd]{revtex}); to appear in Phys. Rev. Let

Computational capacity of the universe

Merely by existing, all physical systems register information. And by evolving dynamically in time, they transform and process that information. The laws of physics determine the amount of information that a physical system can register (number of bits) and the number of elementary logic operations that a system can perform (number of ops). The universe is a physical system. This paper quantifies the amount of information that the universe can register and the number of elementary operations that it can have performed over its history. The universe can have performed no more than $10^{120}$ ops on $10^{90}$ bits.Comment: 17 pages, TeX. submitted to Natur

Universal simulation of Hamiltonian dynamics for qudits

What interactions are sufficient to simulate arbitrary quantum dynamics in a composite quantum system? Dodd et al. (quant-ph/0106064) provided a partial solution to this problem in the form of an efficient algorithm to simulate any desired two-body Hamiltonian evolution using any fixed two-body entangling N-qubit Hamiltonian, and local unitaries. We extend this result to the case where the component systems have D dimensions. As a consequence we explain how universal quantum computation can be performed with any fixed two-body entangling N-qudit Hamiltonian, and local unitaries.Comment: 13 pages, an error in the "Pauli-Euclid-Gottesman Lemma" fixed, main results unchange

A Buffer Stocks Model for Stabilizing Price of Staple Food with Considering the Expectation of Non Speculative Wholesaler

This paper is a study of price stabilization in the staple food distribution system. All stakeholders experience market risks due to some possibility causes of price volatility. Many models of price stabilization had been developed by employing several approaches such as floor-ceiling prices, buffer funds, export or import taxes, and subsidies. In the previous researches, the models were expanded to increase the purchasing price for producer and decrease the selling price for consumer. Therefore, the policy can influence the losses for non-speculative wholesaler that is reflected by the descending of selling quantity and ascending of the stocks. The objective of this model is not only to keep the expectation of both producer and consumer, but also to protect non-speculative wholesaler from the undesirable result of the stabilization policy. A nonlinear programming model was addressed to determine the instruments of intervention program. Moreover, the result shows that the wholesaler behavior affects the intervention costs. Index Terms Buffer stocks, Price stabilization, Nonlinear programming, Wholesaler behavior

Reduced antimicrobial prescribing during autogenous staphylococcal bacterin therapy: a retrospective study in dogs with pyoderma

Autogenous staphylococcal bacterins are commonly mentioned as treatment for canine recurrent pyoderma but little is known about their efficacy. This retrospective study describes use and assesses efficacy of an autogenous Staphylococcus (pseud)intermedius bacterin in dogs with pyoderma. Frequency and duration of systemic antimicrobial therapy were compared 12 months before and after starting bacterin (Wilcoxon signed-rank test) with data extracted from general practice medical histories

Measurement of conditional phase shifts for quantum logic

Measurements of the birefringence of a single atom strongly coupled to a high-finesse optical resonator are reported, with nonlinear phase shifts observed for intracavity photon number much less than one. A proposal to utilize the measured conditional phase shifts for implementing quantum logic via a quantum-phase gate (QPG) is considered. Within the context of a simple model for the field transformation, the parameters of the "truth table" for the QPG are determined.Comment: 4 pages in Postscript format, including 4 figures (attached as uuencoded version of a gzip-file

A Chandra Study of the Dense Globular Cluster Terzan 5

We report a Chandra ACIS-I observation of the dense globular cluster Terzan 5. The previously known transient low-mass x-ray binary (LMXB) EXO 1745-248 in the cluster entered a rare high state during our August 2000 observation, complicating the analysis. Nevertheless nine additional sources clearly associated with the cluster are also detected, ranging from L_X(0.5-2.5 keV)=5.6*10^{32} down to 8.6*10^{31} ergs/s. Their X-ray colors and luminosities, and spectral fitting, indicate that five of them are probably cataclysmic variables, and four are likely quiescent LMXBs containing neutron stars. We estimate the total number of sources between L_X(0.5-2.5 keV)=10^{32} and 10^{33} ergs/s as 11.4^{+4.7}_{-1.8} by the use of artificial point source tests, and note that the numbers of X-ray sources are similar to those detected in NGC 6440. The improved X-ray position allowed us to identify a plausible infrared counterpart to EXO 1745-248 on our 1998 Hubble Space Telescope NICMOS images. This blue star (F110W=18.48, F187W=17.30) lies within 0.2'' of the boresighted LMXB position. Simultaneous Rossi X-ray Timing Explorer (RXTE) spectra, combined with the Chandra spectrum, indicate that EXO 1745-248 is an ultracompact binary system, and show a strong broad 6.55 keV iron line and an 8 keV smeared reflection edge.Comment: 18 pages, 8 figures, accepted to Ap

Negative entropy and information in quantum mechanics

A framework for a quantum mechanical information theory is introduced that is based entirely on density operators, and gives rise to a unified description of classical correlation and quantum entanglement. Unlike in classical (Shannon) information theory, quantum (von Neumann) conditional entropies can be negative when considering quantum entangled systems, a fact related to quantum non-separability. The possibility that negative (virtual) information can be carried by entangled particles suggests a consistent interpretation of quantum informational processes.Comment: 4 pages RevTeX, 2 figures. Expanded discussion of quantum teleportation and superdense coding, and minor corrections. To appear in Phys. Rev. Let