P. Tombesi et D. Vitali, PHYSICAL REALIZATION OF AN ENVIRONMENT WITH SQUEEZED QUANTUM FLUCTUATIONS VIA QUANTUM-NONDEMOLITION-MEDIATED FEEDBACK, Physical review. A, 50(5), 1994, pp. 4253-4257
We show how a squeezed environment can be obtained by means of a suita
ble feedback of the output signal corresponding to a quantum-nondemoli
tion (QND) measurement of an observable. As an example we show how the
variance of a field quadrature of a cavity mode subject to QND-mediat
ed feedback can be squeezed below the standard quantum limit and that
this actually means that applying feedback is equivalent to coupling t
he mode to a squeezed environment.