Controlling Irreversibility and Directional Flow of Light with Atomic Motion

The Doppler effect of moving atoms can create irreversibility of light. We show that the laser field in electromagnetic induced transparency (EIT) scheme with atomic motion can control the directional propagation of two counter-propagating probe fields in atomic gas cell. The quantum coherence effect serves as an optical transistor. Interference of the two output fields from the cell shows useful feature for determining the mean atomic velocity and can be useful as quantum velocimeter. We also find that the sign of the dispersive phase in EIT has a unique property, which helps to explain certain features in the interference.Comment: 5 pages, 5 figure

Phase Controlled Continuously Entangled Two-Photon Laser with Double Λ\Lambda Scheme

We show that an absolute coherent phase of a laser can be used to manipulate the entanglement of photon pairs of two-photon laser. Our focus is on the generation of a continuous source of entangled photon pairs in the double $\Lambda$ (or Raman) scheme. We study the dependence of steady state entanglement on the phase and laser parameters. We obtain a relationship between entanglement and two-photon correlation. We derive conditions that give steady state entanglement for the Raman-EIT scheme and use it to identify region of steady state macroscopic entanglement. No entanglement is found for the double resonant Raman scheme for any laser parameters.Comment: 6 pages (two-column), 4 figures. submitted to a journal on 14 February 200

Computing the maximum violation of a Bell inequality is NP-complete

The number of steps required in order to maximize a Bell inequality for arbitrary number of qubits is shown to grow exponentially with either the number of steps and the number of parties involved. The proof that the optimization of such correlation measure is a NP-problem is based on an operational perspective involving a Turing machine, which follows a general algorithm. The implications for the computability of the so called {\it nonlocality} for any number of qubits is similar to recent results involving entanglement or similar quantum correlation-based measures.Comment: 5 pages, 2 figures. Comments are welcom

Entanglement between exciton and mechanical modes via dissipation-induced coupling

We analyze the entanglement between two matter modes in a hybrid quantum system consists of a microcavity, a quantum well, and a mechanical oscillator. Although the exciton mode in the quantum well and the mechanical oscillator are initially uncoupled, their interaction through the microcavity field results in an indirect exciton-mode--mechanical-mode coupling. We show that this coupling is a Fano-Agarwal-type coupling induced by the decay of the exciton and the mechanical modes caused by the leakage of photons through the microcavity to the environment. Using experimental parameters and for slowly varying microcavity field, we show that the generated coupling leads to an exciton-mode--mechanical-mode entanglement. The maximum entanglement is achieved at the avoided level crossing frequency, where the hybridization of the two modes is maximum. The entanglement is also very robust against the phonon thermal bath temperature.Comment: 6 pages, 4 figures; published versio

Constraints on Inelastic Dark Matter Signal using ZEPLIN-II Results

There has been an increasing interest on the concept of Inelastic Dark Matter (iDM) - motivated in part by some recent data. We describe the constraints on iDM from the results of the two phase dark matter detector ZEPLIN-II, which has demonstrated strong background discrimination capabilities (>98%). Using previously published estimates of the ZEPLIN-II residual background, the iDM limits presented here exclude a significantly larger iDM parameter space than the limits derived without background subtraction. Moreover, assuming standard xenon quenching factor (qXe) of 0.19, our ZEPLIN-II limits strongly suggest the exclusion of iDM signal claims at >99% C.L., for Weakly Interacting Massive Particles (WIMPs) masses >100 GeV.Comment: 4 pages, 2 figure

Comment on ``Plateaus Observed in the Field profile of Thermal Conductivity in the Superconductor Bi_2Sr_2CaCu_2O_8''

We studied the thermal conductivity of a Bi_2Sr_2CaCu_2O_8 single crystal as a function of a magnetic field ramped up and down and then reversed. As recently discovered by Krishana et al., we observed a field-independent thermal conductivity above a threshold field. However, our measurements show that the magnitude of background thermal conductivity depends on the field profile in the sample. This is incompatible with the interpretation put forward by Krishana and co-workers.Comment: 2 Pages including 1 figur

Cyclic groups and quantum logic gates

We present a formula for an infinite number of universal quantum logic gates, which are $4$ by $4$ unitary solutions to the Yang-Baxter (Y-B) equation. We obtain this family from a certain representation of the cyclic group of order $n$. We then show that this {\it discrete} family, parametrized by integers $n$, is in fact, a small sub-class of a larger {\it continuous} family, parametrized by real numbers $\theta$, of universal quantum gates. We discuss the corresponding Yang-Baxterization and related symmetries in the concomitant Hamiltonian.Comment: 12 pages, no figures. Submitted to Physical Review

Light-to-matter entanglement transfer in optomechanics

We analyze a scheme to entangle the movable mirrors of two spatially separated nanoresonators via a broadband squeezed light. We show that it is possible to transfer the EPR-type continuous-variable entanglement from the squeezed light to the mechanical motion of the movable mirrors. An optimal entanglement transfer is achieved when the nanoresonators are tuned at resonance with the vibrational frequencies of the movable mirrors and when strong optomechanical coupling is attained. Stationary entanglement of the states of the movable mirrors as strong as that of the input squeezed light can be obtained for sufficiently large optomechanical cooperativity, achievable in currently available optomechanical systems. The scheme can be used to implement long distance quantum state transfer provided that the squeezed light interacts with the nanoresonators.Comment: Published versio

Influences of initial streamwise rotation of a droplet under a uniform flow

A spherical droplet is given an initial rotation in the streamwise direction and is impulsively accelerated by a uniform free stream. Numerical results for the deformation and dynamics of the droplet are obtained by utilising a finite volume staggered mesh method with a moving mesh interface tracking scheme. The fluid dynamics videos of the droplet are presented in the Gallery of Fluid Motion, 2010. By initially rotating the droplet in the streamwise direction, the droplet deforms differently depending on the non-dimensional rotation rate, $\Omega^*$. The families of droplet shape are, in ascending $\Omega^*$, biconvex, convex-concave and biconcave. While the biconvex and convex-concave families are due to the compression by the combined vortex ring (the lee side of the interface). The biconcave family is formed because of the huge surface tension at the droplet edge that restrains further deformation there. In a special case, the biconcave family releases the combined vortex ring from the droplet. The release of the vortex ring is observed to be at $Re$ one order of magnitude lower than a similar mechanism observed for the flow past a solid sphere. This release of the vortex ring has led to a series of events and a reduction in $C_D$.Comment: a high resolution (video1) and a low resolution (video2) fluid dynamics videos are include

PI : a Parallel in-memory skip list based Index

Due to the coarse granularity of data accesses and the heavy use of latches, indices in the B-tree family are not efficient for in-memory databases, especially in the context of today's multi-core architecture. In this paper, we present PI, a Parallel in-memory skip list based Index that lends itself naturally to the parallel and concurrent environment, particularly with non-uniform memory access. In PI, incoming queries are collected, and disjointly distributed among multiple threads for processing to avoid the use of latches. For each query, PI traverses the index in a Breadth-First-Search (BFS) manner to find the list node with the matching key, exploiting SIMD processing to speed up the search process. In order for query processing to be latch-free, PI employs a light-weight communication protocol that enables threads to re-distribute the query workload among themselves such that each list node that will be modified as a result of query processing will be accessed by exactly one thread. We conducted extensive experiments, and the results show that PI can be up to three times as fast as the Masstree, a state-of-the-art B-tree based index