Squeezed states of the electromagnetic field have been generated by nondegenerate four-wave mixing due to Na atoms in an optical cavity. The optical noise in the cavity, comprised of primarily vacuum fluctuations and a small component of spontaneous emission from the pumped Na atoms, is amplified in one quadrature of the optical field and deamplified in the other quadrature. These quadrature components are measured with a balanced homodyne detector. The total noise level in the deamplified quadrature drops below the vacuum noise level.

Observation of squeezed states generated by four-wave mixing in an optical cavity

The author reviews methods for generating sub-Poissonian light and related concepts. This light has energy fluctuations reduced below the level which corresponds to a classical Poissonian process (shot-noise level). After an introduction to the concept of nonclassical light, an overview is given of the main methods of quantum-noise reduction. Sub-Poissonian processes are exemplified in different areas of optics, ranging from single-atom resonance fluorescence to nonlinear optics, laser physics, and cavity quantum electrodynamics. Emphasis is placed on the conceptual foundations, and on developments in laser theory that lead to the possibility, already demonstrated experimentally, of linewidth narrowing and sub-Poissonian light generation in lasers and masers. The sources of quantum noise in these devices are analyzed, and four noise-suppression methods are discussed in detail: regularization of the pumping, suppression of spontaneous-emission noise, nonadiabatic evolution of the atomic variables, and twin-beam generation.

https://www.if.ufrj.br/~ldavid/arquivos/rmp.pdf

Sub-Poissonian processes in quantum optics

A theoretical investigation of cavity QED effects in semiconductor microcavities containing quantum wells is presented. A model Hamiltonian is used to derive equations of motion for the quantum photon and exciton fields in the cavity. Quantum effects such as squeezing and antibunching are predicted in the light field going out of the cavity under irradiation by a coherent laser field, if exciton-phonon scattering is weak enough. Exciton-phonon scattering is shown to destroy the nonclassical effects and to yield excess noise in the output field.

https://iopscience.iop.org/article/10.1088/1464-4266/1/1/001/pdf

Cavity QED effects in semiconductor microcavities

Optical switching by variation of the squeezing phase

We study the spectrum of squeezing in the light transmitted by a system of two-level atoms in an optical cavity driven by a coherent field, as recently observed by Kimble and collaborators. Our analysis does not introduce any restriction on the detuning parameters or on the relative order of magnitude of the atomic and cavity relaxation rates. Using the dressed-mode formalism, we derive explicit analytic expressions for the spectrum of squeezing and for the second-order intensity correlation function. We describe how the spectrum depends on the various parameters of the system; this study provides general indications on how to optimize the conditions to observe squeezing in optical bistability. A special attention is devoted to the changes of the spectrum under variation of the detuning parameters or of the ratio of cavity to atomic-damping rate. In all cases, the changes are continuous and smooth, with quantitative variations in the level of squeezing. This indicates the existence of a single avenue to squeezing in this system. The bad-cavity direction is identified as especially conventient to obtain a significant amount of squeezing.

Squeezing in optical bistability without adiabatic elimination

Some recent relevant experiments of the Austin group1–3 attained the generation of squeezed states by a system of two-level atoms contained in an optical cavity and driven by a coherent incident field. This type of system is fundamental in quantum optics, and since the mid seventies has been the object of the extensive literature on optical bistability (OB) (see e.g. Ref.4). The squeezing problem in this system is studied in Refs. 5–14.

F. Castelli

Papers

Squeezing in optical bistability without adiabatic elimination

Squeezing in Optical Bistability