22,314 research outputs found
Violation of Bell's inequality using classical measurements and non-linear local operations
We find that Bell's inequality can be significantly violated (up to
Tsirelson's bound) with two-mode entangled coherent states using only homodyne
measurements. This requires Kerr nonlinear interactions for local operations on
the entangled coherent states. Our example is a demonstration of
Bell-inequality violations using classical measurements. We conclude that
entangled coherent states with coherent amplitudes as small as 0.842 are
sufficient to produce such violations.Comment: 6 pages, 5 figures, to be published in Phys. Rev.
Purification and detection of entangled coherent states
In [J. C. Howell and J. A. Yeazell, Phys. Rev. A 62, 012102 (2000)], a
proposal is made to generate entangled macroscopically distinguishable states
of two spatially separated traveling optical modes. We model the decoherence
due to light scattering during the propagation along an optical transmission
line and propose a setup allowing an entanglement purification from a number of
preparations which are partially decohered due to transmission. A purification
is achieved even without any manual intervention. We consider a nondemolition
configuration to measure the purity of the state as contrast of interference
fringes in a double-slit setup. Regarding the entangled coherent states as a
state of a bipartite quantum system, a close relationship between purity and
entanglement of formation can be obtained. In this way, the contrast of
interference fringes provides a direct means to measure entanglement.Comment: 9 pages, 6 figures, using Revtex
Bound on distributed entanglement
Using the convex-roof extended negativity and the negativity of assistance as
quantifications of bipartite entanglement, we consider the possible
remotely-distributed entanglement. For two pure states and
on bipartite systems and , we first show that the
possible amount of entanglement remotely distributed on the system by
joint measurement on the system is not less than the product of two
amounts of entanglement for the states and
in two-qubit and two-qutrit systems. We also provide some sufficient
conditions, for which the result can be generalized into higher-dimensional
quantum systems.Comment: 5 page
Production of superpositions of coherent states in traveling optical fields with inefficient photon detection
We develop an all-optical scheme to generate superpositions of
macroscopically distinguishable coherent states in traveling optical fields. It
non-deterministically distills coherent state superpositions (CSSs) with large
amplitudes out of CSSs with small amplitudes using inefficient photon
detection. The small CSSs required to produce CSSs with larger amplitudes are
extremely well approximated by squeezed single photons. We discuss some
remarkable features of this scheme: it effectively purifies mixed initial
states emitted from inefficient single photon sources and boosts negativity of
Wigner functions of quantum states.Comment: 13 pages, 9 figures, to be published in Phys. Rev.
Generation of macroscopic superposition states with small nonlinearity
We suggest a scheme to generate a macroscopic superposition state
(Schrodinger cat state) of a free-propagating optical field using a beam
splitter, homodyne measurement and a very small Kerr nonlinear effect. Our
scheme makes it possible to considerably reduce the required nonlinear effect
to generate an optical cat state using simple and efficient optical elements.Comment: Significantly improved version, to be published in PRA as a Rapid
Communicatio
Conditional Production of Superpositions of Coherent States with Inefficient Photon Detection
It is shown that a linear superposition of two macroscopically
distinguishable optical coherent states can be generated using a single photon
source and simple all-optical operations. Weak squeezing on a single photon,
beam mixing with an auxiliary coherent state, and photon detecting with
imperfect threshold detectors are enough to generate a coherent state
superposition in a free propagating optical field with a large coherent
amplitude () and high fidelity (). In contrast to all
previous schemes to generate such a state, our scheme does not need photon
number resolving measurements nor Kerr-type nonlinear interactions.
Furthermore, it is robust to detection inefficiency and exhibits some
resilience to photon production inefficiency.Comment: Some important new results added, to appear in Phys.Rev.A (Rapid
Communication
- …