Anomalous Quantum Correlations of Squeezed Light

Three different noise moments of field strength, intensity, and their correlations are simultaneously measured. For this purpose a homodyne cross-correlation measurement [1] is implemented by superimposing the signal field and a weak local oscillator on an unbalanced beam splitter. The relevant information is obtained via the intensity noise correlation of the output modes. Detection details like quantum efficiencies or uncorrelated dark noise are meaningless for our technique. Yet unknown insight in the quantumness of a squeezed signal field is retrieved from the anomalous moment, correlating field strength with intensity noise. A classical inequality including this moment is violated for almost all signal phases. Precognition on quantum theory is superfluous, as our analysis is solely based on classical physics.

Figure 1

Experimental setup for the generation and detection of squeezed light. The squeezed field is generated in an OPA. The flip mirrors F1 and F2 are used to send the squeezed field either to the BHD or the HCCM device.

Figure 2

Measured correlation $C(\varphi )$ (markers) as a function of phase. The error bars of one standard deviation statistical uncertainty are within the size of the markers. The fit according to Eq. (8) is shown by the thin solid curve, composed of the contributions $C_0$, $C_1$, and $C_2$.

Figure 3

Measured correlation $C(\varphi )$ (filled markers) and $C(\varphi +\pi )$ (unfilled markers) for $\varphi =3\pi /4$ as a function of the rescaled LO field strength ${\tilde{E}}_L$. The error bars of one standard deviation statistical uncertainty are within the size of the markers. The quadratic fits are the thin solid and dashed curves, composed of the contributions $C_0$, $C_1$, and $C_2$.

Figure 4

The solid line shows $\det [L(\varphi )]$ as a function of phase as obtained through separation by different phase periodicity. Because of the $\pi$ periodicity of the plot, we confine ourselves to the interval $[0,\pi ]$. The thin dashed lines correspond to an error of one standard deviation. The thick dashed line marks the border between the classical and nonclassical regions. Squeezing is present within the light-colored interval. The marker at $\varphi =3\pi /4$ (antisqueezed region) follows from the separation by the LO field strength, from data measured for $\varphi$ and $\varphi +\pi$. The error corresponds to one standard deviation.