27,691 research outputs found
Testing Bell inequalities with photon-subtracted Gaussian states
Recently, photon subtracted Gaussian states (PSGSs) were generated by several
experimental groups. Those states were called "Schr\"odinger kittens" due to
their similarities to superpositions of coherent states (SCSs) with small
amplitudes. We compare the ideal SCSs and the PSGSs for experimental tests of
certain types of Bell inequalities. In particular, we analyze the effects of
the key experimental components used to generate PSGSs: mixedness of the
Gaussian states, limited transmittivity of the beam splitter and the avalanche
photodetector which cannot resolve photon numbers. As a result of this
analysis, the degrees of mixedness and the beam splitter transmittivity that
can be allowed for successful tests of Bell inequalities are revealed.Comment: 9 pages, 7 figures, to be published in Phys. Rev.
Faithful test of non-local realism with entangled coherent states
We investigate the violation of Leggett's inequality for non-local realism
using entangled coherent states and various types of local measurements. We
prove mathematically the relation between the violation of the
Clauser-Horne-Shimony-Holt form of Bell's inequality and Leggett's one when
tested by the same resources. For Leggett inequalities, we generalize the
non-local realistic bound to systems in Hilbert spaces larger than
bidimensional ones and introduce an optimization technique that allows to
achieve larger degrees of violation by adjusting the local measurement
settings. Our work describes the steps that should be performed to produce a
self-consistent generalization of Leggett's original arguments to
continuous-variable states.Comment: 8 pages, 6 figures, to be published in Phys. Rev.
Effects of squeezing on quantum nonlocality of superpositions of coherent states
We analyze effects of squeezing upon superpositions of coherent states (SCSs)
and entangled coherent states (ECSs) for Bell-inequality tests. We find that
external squeezing can always increase the degrees of Bell violations, if the
squeezing direction is properly chosen, for the case of photon parity
measurements. On the other hand, when photon on/off measurements are used, the
squeezing operation can enhance the degree of Bell violations only for moderate
values of amplitudes and squeezing. We point out that a significant improvement
is required over currently available squeezed SCSs in order to directly
demonstrate a Bell-inequality violation in a real experiment.Comment: 7 pages, 4 figures, accepted for publication in Phys. Rev.
Testing non-local realism with entangled coherent states
We investigate the violation of non-local realism using entangled coherent
states (ECS) under nonlinear operations and homodyne measurements. We address
recently proposed Leggett-type inequalities, including a class of optimized
incompatibility ones and thoroughly assess the effects of detection
inefficiency.Comment: 7 pages, 6 figures, RevTeX4, accepted for publication in Phys. Rev.
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.
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.
Transfer of Nonclassical Properties from A Microscopic Superposition to Macroscopic Thermal States in The High Temperature Limit
We present several examples where prominent quantum properties are
transferred from a microscopic superposition to thermal states at high
temperatures. Our work is motivated by an analogy of Schrodinger's cat paradox,
where the state corresponding to the virtual cat is a mixed thermal state with
a large average photon number. Remarkably, quantum entanglement can be produced
between thermal states with nearly the maximum Bell-inequality violation even
when the temperatures of both modes approach infinity.Comment: minor corrections, acknowledgments added, Phys.Rev.Lett., in pres
Depressed clad hollow optical fiber with fundamental LP01 mode cut-off
We propose a depressed clad hollow optical fiber with fundamental (LP01) mode cut-off suitable for high power short-wavelength, especially three-level, fiber laser operation by introducing highly wavelength dependent losses at longer wavelengths. The cut-off characteristic of such fiber structure was investigated. A Yb-doped depressed clad hollow optical fiber laser generating 59.1W of output power at 1046nm with 86% of slope efficiency with respect to the absorbed pump power was realised by placing the LP01 mode cut-off at ~1100nm
Testing quantum nonlocality by generalized quasiprobability functions
We derive a Bell inequality based on a generalized quasiprobability function
which is parameterized by one non-positive real value. Two types of known Bell
inequalities formulated in terms of the Wigner and Q functions are included as
limiting cases. We investigate violations of our Bell inequalities for single
photon entangled states and two-mode squeezed vacuum states when varying the
detector efficiency. We show that the Bell inequality for the Q function allows
the lowest detection efficiency for violations of local realism.Comment: 6 pages, 3 figure
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