4,136 research outputs found
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 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
(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 by unitary solutions to the Yang-Baxter (Y-B) equation. We
obtain this family from a certain representation of the cyclic group of order
. We then show that this {\it discrete} family, parametrized by integers
, is in fact, a small sub-class of a larger {\it continuous} family,
parametrized by real numbers , 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,
. The families of droplet shape are, in ascending ,
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 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 .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
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