35,955 research outputs found
Kepstrum approach to real-time speech-enhancement methods using two microphones
The objective of this paper is to provide improved real-time noise canceling performance by using
kepstrum analysis. The method is applied to typically existing two-microphone approaches using
modified adaptive noise canceling and speech beamforming methods. It will be shown that the kepstrum
approach gives an improved effect for optimally enhancing a speech signal in the primary input when it
is applied to the front-end of a beamformer or speech directivity system. As a result, enhanced
performance in the form of an improved noise reduction ratio with highly reduced adaptive filter size can
be achieved. Experiments according to 20cm broadside microphone configuration are implemented in
real-time in a real environment, which is a typical indoor office with a moderate reverberation condition
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.
Entangled coherent states versus entangled photon pairs for practical quantum information processing
We compare effects of decoherence and detection inefficiency on entangled
coherent states (ECSs) and entangled photon pairs (EPPs), both of which are
known to be particularly useful for quantum information processing (QIP). When
decoherence effects caused by photon losses are heavy, the ECSs outperform the
EPPs as quantum channels for teleportation both in fidelities and in success
probabilities. On the other hand, when inefficient detectors are used, the
teleportation scheme using the ECSs suffers undetected errors that result in
the degradation of fidelity, while this is not the case for the teleportation
scheme using the EPPs. Our study reveals the merits and demerits of the two
types of entangled states in realizing practical QIP under realistic
conditions.Comment: 9 pages, 6 figures, substantially revised version, 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.
Input-output relations for multiport ring cavities
Quantum input-output relations for a generic -port ring cavity are
obtained by modeling the ring as a cascade of interlinked beam splitters.
Cavity response to a beam impinging on one port is studied as a function of the
beam-splitter reflectivities and the internal phase-shifts. Interferometric
sensitivity and stability are analyzed as a function of the number of ports.Comment: 6 pages, 5 figures (low-res
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