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Physical Review A

Squeezed states in optical cavities: A spontaneous-emission-noise limit

R. E. Slusher, Leo W. Hollberg, Bernard Yurke, Jerome C. Mertz, J. F. Valley

Published May 1, 1985• 59 citations
Publisher

Abstract

Squeezed states of light have been predicted to be generated by four-wave mixing in cavity configurations. Any noise fields in the cavity can degrade or modify these squeezed states. An experiment using a Na atomic beam as the nonlinear mixing medium shows that spontaneous emission from the excited atoms results in a broadband frequency spectrum of noise in the cavity used for squeezing. The limits this noise places on the observed amount of squeezing and possible techniques for avoiding this noise source are discussed.

DOI
10.1103/physreva.31.3512

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Generation of Squeezed States by Four-Wave-Mixing in a Cavity

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Ways to minimize spontaneous-emission noise due to quantum fluctuations in the medium are a major consideration in experiments designed to produce squeezed states of light. Motivated by the recent experiments of Slusher et al. we present a fully quantized model of nondegenerate four-wave mixing. We show that the spontaneous-emission noise, important at higher intensities in the degenerate case, may be minimized in the nondegenerate case for certain regimes of cavity and medium parameters.

Physical Review A•Jun 1, 1986•29 citations
Squeezed states of light have been predicted to be generated by four-wave mixing in cavity configurations. Any noise fields in the cavity can degrade or modify these squeezed states. An experiment using a Na atomic beam as the nonlinear mixing medium shows that spontaneous emission from the excited atoms results in a broadband frequency spectrum of noise in the cavity used for squeezing. The limits this noise places on the observed amount of squeezing and possible techniques for avoiding this noise source are discussed.
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.
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.
Squeezed light generated by four-wave mixing near the Na atomic resonance is compared with a full quantum-theoretical model. Losses and dephasing that are due to spontaneous emission near the atomic resonance are included in this theoretical treatment. The experimental results show noise reduction greater than 1 dB below the standard quantum limits and are in good agreement with the quantum model at low pump intensities and large detuning. Theory and experiment show that limits to squeezed-light noise reduction resulting from spontaneous-emission losses can be largely avoided by using nondegenerate four-wave mixing and pump intensities near the atomic saturation values.
Phase dependent nonlinear optical processes can make large fractional changes in the phase and amplitude of an optical field. An example is the prediction(1) that four-wave-mixing can generate squeezed states of an optical field where the variance in the two quadratures of the field are unequal. In order to observe squeezed states and utilize them in interferometric measurements this inequality in variances must be large (e.g. ≳ 50%). The large phase shifts required to achieve this regime of squeezing can be obtained near the threshold for oscillation of four-wave-mixing in an optical cavity. (2) This paper describes an experimental study(3) of four-wave-mixing in a cavity near threshold using the nonlinear index of the Na atomic resonance.