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Annual Meeting Optical Society of America

Squeezed states: an overview

Bernard Yurke

Published Jan 1, 1986• 0 citations

Abstract

A squeezed state of the electromagnetic field has less noise in one of its two amplitude components than that of a coherent state. This property makes squeezed states potentially useful in low noise and precision measurement. Squeezed states may be generated by, among other things, degenerate parametric amplifiers and four-wave mixers. The reduced noise in one of the amplitude components is most easily observed via a homodyne detector. A number of experimental efforts to generate and detect squeezed states are under way. Here, in describing experimental techniques, the experiments' carried out by Slusher et al. are emphasized. A number of techniques were employed to successfully generate squeezed light. An atomic beam of sodium provided the optical nonlinearity in a cavity-backward four-wave mixer. By employing pairs of Fabry-Perot modes spaced symmetrically about the pump frequency, squeezed light was generated in nondegenerate conditions where Rayleigh scattering of pump light could be avoided. To observe squeezing, a number of nonidealities such as phase jitter and detector inefficiencies also had to be overcome.

DOI: 10.1364/oam.1986.tua1

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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.

Four-wave mixers have been investigated theoretically as potential sources of squeezed-coherent radiation 1,2 and there are a number of experimental efforts underway to demonstrate the production of squeezed-coherent radiation via such devices.3,4,5 Here the results of some wideband calculations of the output of cavity four-wave mixers is presented. The wideband squeezed-coherent radiation generated by such devices may be detected via a wideband homodyne detector.6 Wideband squeezing will manifest itself in the noise-power spectrum of the homodyne detector's output as regions where the noise is reduced below the level that is observed when no light enters the input port of the homodyne detector. Wideband homodyne detection allows one to look for squeezing at frequencies far from d.c. This gives the experimentalist the freedom to look for squeezing in the frequency range where his detector performs best.

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.

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Wideband calculations of the response of a homodyne detector to the outputs of various four-wave-mixer configurations are presented. It is shown that the noise-power spectrum of the homodyne detector output can exhibit regions where the noise is greatly reduced below the shot-noise level even at frequencies far from dc. Hence, in the detection of noise squeezing via homodyne detectors, 1/f noise and other low-frequency noise sources may be avoided by observing the homodyne detector's noise power at frequencies far from dc.