ISSN:0950-0340    

DOI:10.1080/09500349414552101

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We describe the experimental observation and theoretical interpretation of a squeezing effect which occurs through the coupling of two light beams in a three-level atomic system. The origin of this effect can be attributed to the transfer of the intensity fluctuations of one beam to the phase fluctuations of the other one, followed by an optical feedback onto the intensity of the initial beam. The first step of the information transfer is similar to the one which occurs in a quantum non-demolition (QND) measurement of the intensity. The feedback effect is obtained through mixing of the phase and intensity quadratures, due to the detuning of the optical cavity which contains the nonlinear medium. Therefore the information obtained by the QND measurement is used to correct the intensity fluctuations of the signal beam by a build-in mechanism, which does not require any use of external electronics.

ISSN:0950-0340    

DOI:10.1080/09500349414552111

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The squeezing properties of the Raman scattering process which takes place when the lower output frequency from a non-degenerate optical parametric interaction approaches a resonance of the nonlinear medium placed inside an optical resonant cavity are presented. The linear stability analysis is performed and the spectrum for the output fields is given in terms of the quadrature phase components in the Wigner representation. Perfect squeezing for the amplitude difference between the output Stokes and anti-Stokes modes at the Hopf bifurcation point is obtained.

ISSN:0950-0340    

DOI:10.1080/09500349414552121

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this paper, we analyse the properties of a quantum state transformation system consisting of a squeezer and an optical Kerr medium. An average, a variance, and a signal-to-noise ratio (SNR) of a quadrature-phase amplitude are calculated analytically. We show that the SNR is increased by this system; in particular the use of a squeezer with a large squeezing gain gives a drastic improvement in the SNR. Furthermore, the reason for the improvement in SNR and the usefulness of the squeezed state are discussed.

ISSN:0950-0340    

DOI:10.1080/09500349414552131

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

It is shown that the performance of optical communication systems that use pulse position modulation and direct photon counting can be improved with the use of squeezed states. The effect of noise is studied. An improved version of the pulse position modulation called extended position modulation is also considered.

ISSN:0950-0340    

DOI:10.1080/09500349414552141

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We report on the time evolution of the Wehrl entropy in a Kerr-like medium. We show that the Wehrl entropy gives a clear signature for the formation of finite superpositions of coherent states (cat-like states). In addition, the actual value of the Wehrl entropy at the time of a superposition formation gives the number of coherent components taking part in the superposition.

ISSN:0950-0340    

DOI:10.1080/09500349414552151

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We inquire under what conditions some of the information in a quantum signal source, namely a set of pure states ψaemitted with probabilitiespa, can be extracted in classical form by a measurement leaving the quantum system with less entropy than it had before, but retaining the ability to regenerate the source state exactly from the classical measurement result and the after-measurement state of the quantum system. We show that this can be done if and only if the source states ψafall into two or more mutually orthogonal subsets.

ISSN:0950-0340    

DOI:10.1080/09500349414552161

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We propose a definition of fidelity for mixed quantum states in terms of Uhlmann's ‘transition probability’ formulaF(ϱ1, ϱ2) = {trace [(√ϱ1ϱ2× √ϱ1)1/2]}2and give new elementary proofs of its essential properties.

ISSN:0950-0340    

DOI:10.1080/09500349414552171

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The number-quadrature minimum-uncertainty states after rotation and displacement emerge in the parametric down-conversion followed by photon number measurement in the idler mode when the coherent state inputs. Again, the state generated in the signal mode by the reduction is described by the principally measurable quantum-statistical tools.

ISSN:0950-0340    

DOI:10.1080/09500349414552181

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We give an account of the quantum noiseless coding theorem, including a new proof based on a simplified block coding scheme. We also discuss an illustrative example of quantum coding.

ISSN:0950-0340    

DOI:10.1080/09500349414552191

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor