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Physical Review A

Nonequilibrium Green-function theory of quantum-optical correlations

Christopher J. Mertens, T. A. B. Kennedy

Published May 1, 1996• 9 citations
Publisher

Abstract

A method for the the derivation and truncation of correlation function hierarchies for Markovian damped quantum-optical systems is presented. The theory enables the inclusion of multiphoton scattering processes which are ignored in conventional semiclassical theories. These produce observable dynamical signatures which depend on characteristic scales of photon number. Applications of the theory to intracavity optical parametric oscillation and second-harmonic generation are given. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physreva.53.3497

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A method for the the derivation and truncation of correlation function hierarchies for Markovian damped quantum-optical systems is presented. The theory enables the inclusion of multiphoton scattering processes which are ignored in conventional semiclassical theories. These produce observable dynamical signatures which depend on characteristic scales of photon number. Applications of the theory to intracavity optical parametric oscillation and second-harmonic generation are given. \textcopyright{} 1996 The American Physical Society.
A many-body theory of quantum fluctuations in the optical parametric oscillator is given. Dyson equations and diagrammatic representation of photon Green functions are derived from a combination of quantum Langevin and many-body techniques. Single-photon Green functions are used to compute dynamic spectra of the output using a self-consistent scheme which incorporates nonlinear, many-photon polarization effects. The latter scale with system size and their influence on the nonlinear quantum dynamics is addressed. We present results of dynamic output spectra and quantum-noise properties beyond the adiabatic approximation.
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The dynamics of correlation function of quantum fluctuations of quadrature amplitudes, as well as the dynamics of correlation function of quantum fluctuations of photon-numbers of fundamental and the third-harmonics mode are investigated for the process of intracavity generation of the third-harmonic. In the case of the evolution of system from initial vacuum state of both modes into the region of great times of interaction, both correlation functions tend to the stationary value. It is shown that these correlations depend strongly on the non-linear coupling coefficient between these modes. In the case of small coupling coefficients the correlation of fluctuations of the quadrature amplitudes as well as the correlation of fluctuations of photon-number are weak. As the coupling coefficient is rising both correlations are also rising (the state of the sub-systems becomes more entangled by the corresponding variables). By further rise of the coupling coefficient the correlation of quadrature amplitudes of fluctuations vanishes (the entanglement of subsystem states over the quadrature amplitudes is also vanishing) but the correlation of fluctuations of the photon-numbers is not vanishing (the subsystems remain entangled over the photon-number variables).
Abstract In quantum statistics based on many-body Green’s functions, the effective medium is represented by the selfenergy. This book aims to discuss the selfenergy from this point of view. The knowledge of the exact selfenergy is equivalent to the knowledge of the exact correlation function from which one can evaluate any single-particle observable. Complete interpretations of the selfenergy are as rich as the properties of the many-body systems. It will be shown that classical features are helpful to understand the selfenergy, but in many cases we have to include additional aspects describing the internal dynamics of the interaction. The inductive presentation introduces the concept of Ludwig Boltzmann to describe correlations by the scattering of many particles from elementary principles up to refined approximations of many-body quantum systems. The ultimate goal is to contribute to the understanding of the time-dependent formation of correlations. Within this book an up-to-date most simple formalism of nonequilibrium Green’s functions is presented to cover different applications ranging from solid state physics (impurity scattering, semiconductor, superconductivity, Bose–Einstein condensation, spin-orbit coupled systems), plasma physics (screening, transport in magnetic fields), cold atoms in optical lattices up to nuclear reactions (heavy-ion collisions). Both possibilities are provided, to learn the quantum kinetic theory in terms of Green’s functions from the basics using experiences with phenomena, and experienced researchers can find a framework to develop and to apply the quantum many-body theory straight to versatile phenomena.
Quantum properties of intracavity nonlinear optical processes such as parametric oscillation and second harmonic generation are limited to a linearized analytical treatment except for certain special cases. Perfect squeezing in one quadrature and the divergence in fluctuations of the conjugate quadrature predicted at threshold in parametric oscillation are a consequence of the approximate linearized analysis. We investigate nonlinear quantum fluctuation corrections by using nonequilibrium Green’s function methods1,2 in concert with quantum master equations, to assess when these system-size effects may be observable in the laboratory.