Classical Signature of Ponderomotive Squeezing in a Suspended Mirror Resonator

The radiation pressure coupling between a low-mass moving mirror and an incident light field has been experimentally studied in a high-finesse Fabry-Perot cavity. Using classical intensity noise in order to mimic radiation pressure quantum fluctuations, the physics of ponderomotive squeezing comes into play as a result of the opto-mechanical correlations between the field quadratures. The same scheme can be used to probe ponderomotive squeezing at the quantum level, thus opening new routes in quantum optics and high sensitivity measurement experiments.

Figure 1

(a) Image of the double wheel oscillator. (b) FEM calculation of the fundamental mode. (c) Scheme of the experimental apparatus. Optical isolator (O.I.); acousto-optic modulator (AOM); electro-optic modulator (EOM); half-wave plate (H); quarter-wave plate (Q); photodiode (PD); polarizing beam splitter (PBS); beam splitter (BS).

Figure 2

Spectral density of the cavity length fluctuations measured without (black) or in presence of the signal beam with added intensity noise (green). The red curve is a thermal noise fit through the expression of $S_x^{\mathrm{th}}$ given in the text, at room temperature.

Figure 3

Noise spectra of the reflected signal beam as the homodyne angle is varied. From upper to lower trace: (a) $\varphi =0$ (black), $\varphi =-20°$ (blue), $\varphi =-44°$ (green), $\varphi =-56°$ (red). (b) $\varphi =26°$ (black), $\varphi =35°$ (blue), $\varphi =45°$ (green), $\varphi =62°$ (red). Dashed lines are used for the theoretical curves.

Figure 4

Noise spectral density, normalized to its standard quantum level, calculated for the parameters given in the text and a homodyne angle of ${10}^{-4}\mathrm{rad}$ (thick black line). Also shown are the different contributions to the total noise: vacuum fluctuations entering through cavity losses (blue line) and in the beam-splitter that divides signal and local oscillator (dashed red line); laser amplitude noise (green); laser frequency noise (violet); mirror thermal noise (light blue, dashed line).