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arXiv:0906.4071 · Physical Review A

Extra phase noise from thermal fluctuations in nonlinear optical crystals

J. E. S. César, A. S. Coelho, K. N. Cassemiro, Alessandro S. Villar, Mikael Lassen, P. Nussenzveig, M. Martinelli

Published Jun 11, 2009• 39 citations
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Abstract

We show theoretically and experimentally that scattered light by thermal phonons inside a second-order nonlinear crystal is the source of additional phase noise observed in optical parametric oscillators. This additional phase noise reduces the quantum correlations and has hitherto hindered the direct production of multipartite entanglement in a single nonlinear optical system. We cooled the nonlinear crystal and observed a reduction in the extra noise. Our treatment of this noise can be successfully applied to different systems in the literature.

DOI
10.1103/physreva.79.063816

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We review the measurement of entanglement in the above-threshold optical parametric oscillator, an experimental challenge that lasted 17 years. The challenge was in part technical, owing to the difficulty of measuring phase noise, but also related to unexpected noise features that remain unexplained. We describe the experimental strategies used to measure phase noise and to circumvent the "extra" noise. The theoretical prediction of a higher order of entanglement is presented, as well as measurements of bright three-color quantum correlations.
Quantum states with non-Gaussian statistics generated by optical parametric oscillators (OPO) with fluctuating parameters are studied by means of the kurtosis excess of the external field quadratures. The field generated is viewed as the response of a nonlinear device to the fluctuations of pump laser amplitude and frequency, crystal temperature, and cavity detuning, in addition to quantum noise sources. The kurtosis excess has been evaluated perturbatively up to the third order in the strength of the crystal nonlinear coupling factor and the second order in the classical fluctuating parameters. Applied to the device described in Opt. Expr. 13, 948 (2005), the model has given values of the kurtosis excess in good agreement with the measured ones.