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Observation of Squeezed States Generated by Four-Wave Mixing in an Optical Cavity

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Abstract

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 are specially designed non-canonical initial states which have a smaller variance in quadrature than that of a coherent state [1][2][3][4]. These quantum states form an exotic choice of initial states when studying atom-photon interactions in open quantum systems [5,6]. Squeezed states of light have been shown to exhibit non-trivial effects on system observables like quadrature autocorrelations in atom-cavity systems and higher order correlated photon pairs from MgO:LiNbO 3 crystals. ...
... In our case, we numerically evaluate the quantity F A as a function of x L and x R and show the results graphically in Figs. (5) and (6). We see that the inequality holds for the entire range of x L and x R for a wide range of n L and n R values. ...
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... A prominent example of non-classical states is the set of squeezed states, in which the fluctuation associated with one quadrature component is below the vacuum state 39 . Early theoretical work in the 60s and 80s led to the conclusion that quantum fluctuations can be reduced below the shot noise in many forms of nonlinear optical interactions [40][41][42] . For example, squeezed states are produced in nonlinear processes called degenerate parametric down-conversion, where a "classical" electromagnetic field drives a nonlinear www.nature.com/scientificreports/ ...
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