963 research outputs found
A theorem for the beam splitter entangler
It is conjectured that the an entanglement output states from a beam splitter
requires the nonclassicality in the input state(M.S. Kim, W. Son, V. Buzek and
P. L. Knight, Phys. Rev. A, 65, 032323(2002)). Here we give a proof for this
conjecture.Comment: Two relevant literatures added. To appear in Phys. Rev.
Continuous-variable quantum teleportation of entanglement
Entangled coherent states can be used to determine the entanglement fidelity
for a device that is designed to teleport coherent states. This entanglement
fidelity is universal, in that the calculation is independent of the use of
entangled coherent states and applies generally to the teleportation of
entanglement using coherent states. The average fidelity is shown to be a poor
indicator of the capability of teleporting entanglement; i.e., very high
average fidelity for the quantum teleportation apparatus can still result in
low entanglement fidelity for one mode of the two-mode entangled coherent
state.Comment: 5 pages, 1 figure, published versio
Properties of a beam splitter entangler with Gaussian input states
An explicit formula is given for the quantity of entanglement in the output
state of a beam splitter, given the squeezed vacuum states input in each mode.Comment: To appear in Phys. Rev.
Quantum Walks driven by many coins
Quantum random walks have been much studied recently, largely due to their
highly nonclassical behavior. In this paper, we study one possible route to
classical behavior for the discrete quantum random walk on the line: the use of
multiple quantum ``coins'' in order to diminish the effects of interference
between paths. We find solutions to this system in terms of the single coin
random walk, and compare the asymptotic limit of these solutions to numerical
simulations. We find exact analytical expressions for the time-dependence of
the first two moments, and show that in the long time limit the ``quantum
mechanical'' behavior of the one-coin walk persists. We further show that this
is generic for a very broad class of possible walks, and that this behavior
disappears only in the limit of a new coin for every step of the walk.Comment: 36 pages RevTeX 4.0 + 5 figures (encapsulated Postscript). Submitted
to Physical Review
Generation of two-mode nonclassical states and a quantum phase gate operation in trapped ion cavity QED
We propose a scheme to generate nonclassical states of a quantum system,
which is composed of the one-dimensional trapped ion motion and a single cavity
field mode. We show that two-mode SU(2) Schr\"odinger-cat states, entangled
coherent states, two-mode squeezed vacuum states and their superposition can be
generated. If the vibration mode and the cavity mode are used to represent
separately a qubit, a quantum phase gate can be implemented.Comment: to appear in PR
Multipartite entangled coherent states
We propose a scheme for generating multipartite entangled coherent states via
entanglement swapping, with an example of a physical realization in ion traps.
Bipartite entanglement of these multipartite states is quantified by the
concurrence. We also use the --tangle to compute multipartite entanglement
for certain systems. Finally we establish that these results for entanglement
can be applied to more general multipartite entangled nonorthogonal states.Comment: 7 pages, two figures. We added more detail discussions on the
generation of multipartite entangled coherent states and multipartite
entangelemen
Simulation of quantum random walks using interference of classical field
We suggest a theoretical scheme for the simulation of quantum random walks on
a line using beam splitters, phase shifters and photodetectors. Our model
enables us to simulate a quantum random walk with use of the wave nature of
classical light fields. Furthermore, the proposed set-up allows the analysis of
the effects of decoherence. The transition from a pure mean photon-number
distribution to a classical one is studied varying the decoherence parameters.Comment: extensively revised version; title changed; to appear on Phys. Rev.
Asymmetric double barrier resonant tunneling structures with improved characteristics
We present a self-consistent calculation, based on the global coherent
tunnelling model, and show that structural asymmetry of double barrier resonant
tunnelling structures significantly modifies the current-voltage
characteristics compared to the symmetric structures. In particular, a suitably
designed asymmetric structure can produce much larger peak current and absolute
value of the negative differential conductivity than its commonly used
symmetric counterpart.Comment: 1 paper, 3 figure
Decoherence can be useful in quantum walks
We present a study of the effects of decoherence in the operation of a
discrete quantum walk on a line, cycle and hypercube. We find high sensitivity
to decoherence, increasing with the number of steps in the walk, as the
particle is becoming more delocalised with each step. However, the effect of a
small amount of decoherence is to enhance the properties of the quantum walk
that are desirable for the development of quantum algorithms. Specifically, we
observe a highly uniform distribution on the line, a very fast mixing time on
the cycle, and more reliable hitting times across the hypercube.Comment: (Imperial College London) 6 (+epsilon) pages, 6 embedded eps figures,
RevTex4. v2 minor changes to correct typos and refs, submitted version. v3
expanded into article format, extra figure, updated refs, Note on "glued
trees" adde
Generation of arbitrary two dimensional motional state of a trapped ion
We present a scheme to generate an arbitrary two-dimensional quantum state of
motion of a trapped ion. This proposal is based on a sequence of laser pulses,
which are tuned appropriately to control transitions on the sidebands of two
modes of vibration. Not more than laser pulses are needed to
generate a pure state with upper phonon number and in the and
direction respectively.Comment: to appear in PR
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