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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Intensity-field and intensity-intensity correlations for a two-level atom in an optical parametric oscillator

C. Elliot Strimbu, Perry R. Rice

Published May 16, 2003• 0 citations
Publisher

Abstract

We consider intensity-field correlation functions for a two-level atom in a degenerate optical parametric oscillator (OPO). Analytic results are obtained in the limit of weak driving fields using quantum trajectory methods. We find large violations of inequalities satisfied by classical fields. We compare our results to those of an ordinary OPO. We also calculate the second-order intensity correlation function for transmitted and fluorescent light, as well as for cross correlations. Here we report large violations of inequalities for the intensity cross-correlation functions in the weak field limit.

DOI
10.1117/12.488878

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We consider intensity-field correlation functions for a two-level atom in a degenerate optical parametric oscillator (OPO). Analytic results are obtained in the limit of weak driving fields using quantum trajectory methods. We find large violations of inequalities satisfied by classical fields. We compare our results to those of an ordinary OPO. We also calculate the second-order intensity correlation function for transmitted and fluorescent light, as well as for cross correlations. Here we report large violations of inequalities for the intensity cross-correlation functions in the weak field limit.
We consider intensity-field correlation functions for a two-level atom in a degenerate optical parametric oscillator (OPO), which would result from a conditioned homodyne measurement. Analytic results are obtained in the limit of weak driving fields using quantum trajectory methods for both the transmitted and fluorescent fields. This system is unique in that after detection of a photon, it is known that one excitation is in the system, in either the atom or cavity mode. We find large violations of inequalities satisfied by classical fields, for both transmitted and fluorescent fields. This is in contrast to the usual cavity QED system of an atom in a driven cavity where we do not find nonclassical behavior in the intensity-field correlation function in fluorescence. This is understood in terms of a relationship between the intensity-field correlation function and the second-order intensity correlation function, as well as the different amount of field-atom entanglement in the two systems. We show that for weak-field cavity QED one must have photon bunching to have nonclassical behavior in the intensity-field correlation function. We compare our results to those of an ordinary OPO. Finally, we also consider cross correlations, where we examine the transmitted (fluorescent) field conditioned by detection of a fluorescent (transmitted) photon.
We investigate intensity cross-correlation functions for two cavity QED systems. These are a driven optical cavity containing a single two-level atom interacting with a single mode of the cavity field with quantized centre of mass motion, and a two-level atom in an optical parametric oscillator. We find analytic results in the weak driving field limit using quantum trajectory theory. We find large violations of inequalities that must be satisfied by classical fields. One of these inequalities is well known, g (2) ij (τ) ≤ √g (2) jj (0)g (2) jj (0), where i and j denote two modes of the field. We also derive a new inequality that cross-correlations must satisfy, |g (2) ij (τ) - 1| 2 ≤ |(g (2) ii (0) - 1)(g (2) jj (0) - 1)|. Large violations of classical inequalities and asymmetrical behaviour in delay time τ are found in complimentary regimes for the cavity QED system with quantized centre of mass motion. They always exist for the two-level atom inside an optical parametric oscillator.
We consider two systems in the weak driving field limit. The first is an optical parametric oscillator, the transmitted field of which is highly bunched. We discuss a conditioned measurement of the second order intensity correlation function that yields antibunching. The second system we consider is a single two level atom inside a weakly driven cavity. Here we consider cross correlations between the transmitted and fluorescent fields. A strong asymmetry in delay time has been noted by Denisov et. al., here we find strong violations of a classical inequality for the cross correlation.
We consider the interaction of a two-level atom inside an optical parametric oscillator. In the weak-driving-field limit, we essentially have an atom-cavity system driven by the occasional pair of correlated photons, or weakly squeezed light. We find that we may have holes, or dips, in the spectrum of the fluorescent and transmitted light. This occurs even in the strong-coupling limit when we find holes in the vacuum-Rabi doublet. Also, spectra with a subnatural linewidth may occur. These effects disappear for larger driving fields, unlike the spectral narrowing obtained in resonance fluorescence in a squeezed vacuum; here it is important that the squeezing parameter N tends to zero so that the system interacts with only one correlated pair of photons at a time. We show that a previous explanation for spectral narrowing and spectral holes for incoherent scattering is not applicable in the present case, and propose an alternative explanation. We attribute these anomalous effects to quantum interference in the two-photon scattering of the system.
We consider a coherently driven two-level atom in an optical parametric oscillator operating below threshold. Applying the Hiesenberg and quantum Langevin equations, we study the power spectrum and the normalised second-order correlation function of the fluorescent light in the weak and strong driving light limits. We also calculate the atomic inversion in the two limiting cases. We find that the widths of the Mollow triplets increases as the degree of squeezing increases and even the side peaks disappear as the amount of squeezing approaches its maximum value. Moreover, the oscillatory nature of the second-order correlation function and the atomic inversion in the strong driving light limit damps out as the degree of squeezing increases.
Resonance fluorescence from a single two-level atom driven by a beam of squeezed light is studied in the weak-field limit. We consider the situation where the atom is coupled to the ordinary vacuum and only a few field modes corresponding to the driving field are squeezed. The field produced by the degenerate optical parametric oscillator is used as the driving field. Heisenberg equations of motion are solved in the steady-state and analytic expressions for the fluorescent-light intensity and the spectrum of fluorescent light are derived. We also consider photon statistics of fluorescent light. In particular, squeezing, antibunching, and sub-Poissonian statistics of fluorescent photons are discussed, and analytic expressions for the quadrature variance and the two-time intensity correlation function are presented. Contrary to the case of coherent excitation, the second-order intensity correlation function does not factorize. This and other differences are discussed, and curves are presented to illustrate the behavior of various quantities. We also present results for thermal excitation of the atom.