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Physical Review A

Linear input-output method for quantum fluctuations in optical bistability with two-level atoms

Laurent Hilico, Claude Fabre, Serge Reynaud, E. Giacobino

Published Oct 1, 1992• 47 citations
Publisher

Abstract

We derive the modifications of the quantum fluctuations of a coherent field after it has interacted with an optical cavity containing an ensemble of two-level atoms. The fluctuations in the output field are separated into two parts: the first one is linked to the parametric transformation of the fluctuations of the incoming field by the atomic medium; the second one is associated with the resonance fluorescence of the atoms driven by the mean intracavity field and coupled with the empty modes of a bath field. We calculate the squeezing spectra and we compare them to the ones obtained with Kerr media having similar dynamic nonlinearities.

DOI
10.1103/physreva.46.4397

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We derive the modifications of the quantum fluctuations of a coherent field after it has interacted with an optical cavity containing an ensemble of two-level atoms. The fluctuations in the output field are separated into two parts: the first one is linked to the parametric transformation of the fluctuations of the incoming field by the atomic medium; the second one is associated with the resonance fluorescence of the atoms driven by the mean intracavity field and coupled with the empty modes of a bath field. We calculate the squeezing spectra and we compare them to the ones obtained with Kerr media having similar dynamic nonlinearities.
A two-photon laser is modeled as NNN two-level atoms interacting via a two-photon transition with a single resonant-cavity field mode. The quadratic form of this interaction makes such a system a candidate to exhibit reduced quantum fluctuations (squeezing) in one quadrature of the output field. A Fokker-Planck equation containing all leading quantum noise terms is derived following the method of Haken. A linearized fluctuation analysis reveals that there is no squeezing in a two-photon laser with injected signal. A small amount of squeezing may be present in two-photon optical bistability. Our calculations confirm the results of Lugiato and Strini, who adopted a factorization of moment equations.
We discuss the optical bistable behavior of a system of N two-level atoms pumped by a coherent input field and coupled to a squeezed vacuum field by treating the optical bistability of such a system as an input-output problem. We consider the equation of motion for atomic dipole moments, coupled to the cavity field and the squeezed vacuum, and the boundary condition connecting the input and output fields with the atomic lowering operator. A simple analytical expression for the influence of the squeezed vacuum input on the bistable behavior of the output field is derived by this method. The results indicate a strong influence of the squeezed vacuum input on optical bistability. The squeezed (stretched) vacuum input field tends to increase (decrease) the range of optical bistability.
A quantum treatment of a coherently driven cavity with a medium of two-level atoms is given. The system displays both absorptive and dispersive bistability. Quantum fluctuations are included via a Fokker-Planck equation in a generalized PPP representation, after adiabatic elimination of the atomic variables. The transmitted spectrum and correlation function is calculated in a linearized (Gaussian) approximation. In the limit of large detuning and radiative damping, the quantum fluctuations are identical to those of a simple nonlinear polarizability theory. An analysis is given of the nonclassical statistical properties of the intensity-correlation spectrum.
A new possibility of generating one-mode squeezed light by coupling a system of two-level atom with a bichromatic pump field in an optical cavity is suggested. The non-classical character of light in this process is caused by two-photon radiation at the central frequency of the spectrum of resonance fluorescence in the bichromatic field. The intensity of the resonance fluorescence cavity output field as well as the variance of the quadrature amplitudes and the second-order correlation function of intensity are calculated.
In Chapter 1 we consider the question of squeezing in a two-photon laser. A two-photon laser is modelled as N two-level atoms interacting via a two-photon transition with a single resonant cavity field mode. A Fokker-Planck equation containing all leading noise terms is derived. A linearised fluctuation analysis reveals that there is no squeezing in a two-photon laser with injected signal. A small amount of squeezing is present in two-photon optical bistability. In Chapter 2 a microscopic model of degenerate four wave mixing including the quantisation of the medium is presented. Time-dependent solutions show ideal squeezing to be obtained in the limits of large detuning, low saturation and zero loss. The effect of nonideal atomic parameters is analysed. Equations describing the spatial propagation of the field through the medium are also derived. In Chapters 3 and 4 we are concerned with quantum effects, in particular violation of Bell's Inequalities, present in optical systems. An optical field produced by an intracavity four wave mixing is shown to exhibit the nonclassical features of photon antibunching, squeezing and violation of Cauchy-Schwarz and Bell's Inequalities. These intrinsic quantum mechanical effects are shown to be associated with the nonexistence of a positive normalizable Glauber-Sudarshan P-function.