L. A. Orozco

Squeezed-state generation in optical bistability

Experiments to generate squeezed states of light are described for a collection of two-level atoms within a high-finesse cavity. The investigation is conducted in a regime for which the weak-field coupling of atoms to the cavity mode produces a splitting in the normal mode structure of the atom-field system that is large compared with the atomic linewidth. Reductions in photocurrent noise of 30% (-1.55 dB) below the noise level set by the vacuum state of the field are observed in a balanced homodyne detector. A degree of squeezing of approximately 50% is inferred for the field state in the absence of propagation and detection losses. The observed spectrum of squeezing extends over a very broad range of frequencies (~±75 MHz), with the frequency of best squeezing corresponding to an offset from the optical carrier given by the normal mode splitting.

Optical Bistability with Two-State Atoms: Steady States and Dynamical Instabilities

A fundamental problem in optical physics is the interaction of two-level atoms with the electromagnetic field of a resonant cavity. Our experiments [1] with two-state sodium atoms are directed towards a quantitative investigation of the steady-state characteristics, dynamical behavior and the quantum statistical nature of the atom-field interaction in such a system. We report absolute comparisons between experiment and the single-mode theory of optical bistability with a Gaussian transverse profile.

Experimental Investigation of the Single-Mode Instability in Optical Bistability

Instabilities in optical systems form a very rich and exciting field of work.1 A great deal of theoretical effort has been devoted to understanding the complex behavior observed in the experiments. Active optical systems such as the laser have attracted more attention than passive systems; among the latter, the driven cavity filled with a collection of two-state atoms represents a canonical system in optical physics.2 Its study has shown optical bistability, instabilities, higher-order dynamical states and non-classical quantum statistics of the transmitted field.3

Generation and Application of Squeezed States of Light

Squeezed states of light have recently been generated in several laboratories by a variety of techniques [1]. As the name implies, squeezed states are states for which the variance in one of two quadrature phase amplitudes is reduced (squeezed) below the level associated with the zero-point or vacuum fluctuations of the electromagnetic field [2]. Because of an uncertainty relation constraining the product of variances, this reduction is necessarily accompanied by an increase in fluctuations above the vacuum level for the orthogonal quadrature-phase amplitude. Squeezed states are of great intrinsic interest from the perspective of quantum optics because of the nonclassical nature of the radiation field in these states. There is as well a growing interest in the potential that squeezed states offer for improvements in the precision of optical measurements and for fundamental spectroscopic investigations. In this brief contribution we review the research program at the University of Texas at Austin relating to the generation and application of squeezed states.

Dynamic Instabilities In Optical Bistability

An experimental study is presented of dynamic instabilities in optical bistability with two-state atoms in a cavity. The basic conceptual simplicity of the system as well as the degree to which it has been quantitatively characterized allows precise comparisons between theory and experiment. Instability boundaries in the parameter space of atomic and cavity detunings, of atomic cooperativity and of intracavity intensity are discussed and compared with theory.

Influence of Cavity Properties on the Interpretation of Experimental Results in Bistability

The analysis of experiments on bistability and instability in nonlinear optical resonators depends critically on an understanding of the properties of the corresponding empty (linear) resonators, Both real and ideal cavities exhibit behavior which can lead to a misinterpretation of experimental results, and in both cases this behavior becomes more pronounced with increasing finesse. As an example of the first case, consider a real cavity which is nonideal in that different methods of measurement of the cavity loss give different values for it and hence for the cooperativity C. A simple but realistic model for such a cavity leads to the derivation of a state equation for bistability which differs in functional form from the usual state equation derived assuming an ideal cavity. In such a nonideal cavity, one might find its loss by measuring the decay time of the transmitted light after rapidly cutting off the incident light or by scanning the length of the cavity to measure the finesse. If these two different values of loss differ by a factor of two, as they have in certain of our experiments, then making either one or the other measurement and applying the usual state equation would cause one to overestimate or underestimate the value of C necessary for the critical onset of bistability by as much as 40%. Exemplifying the second case, the transient regime of even an ideal cavity can exhibit behavior which mimics period doubling, quasiperiodicity, and optical chaos. These appear in the transmission of a cavity excited off-resonance by a pulse with rise or fall times comparable to or shorter than the cavity response time, obscuring the investigation of optical nonlinear dynamics in the transient regime.