Quantum Noise in Homodyne Detection (With 6 Figures)

R. Loudon

Nigel G. Walker, J.E. Carroll

N.J. Shukur

A. J. de Faria

An optical procedure in the context of continuous variables to verify bipartite entanglement without destroying both systems and their entanglement is proposed. To perform the nondestructive verification of entanglement, the method relies on beam-splitter and quantum nondemolition (QND) interactions of the signal modes with two ancillary probe modes. The probe modes are measured by homodyne detections, and the obtained information is used to feed forward modulation of signal modes, concluding the procedure. Characterizing the method by figures of merit used in QND processes, we can establish the conditions for an effectively quantum scheme. Based on such conditions, it is shown that the classical information acquired from the homodyne detections of probe modes is sufficient to verify the entanglement of the output signal modes. The processing impact due to added noise on the output entanglement is assessed in the case of Gaussian modes.

H. Fearn, R. Loudon, Terence J. Shepherd

Expressions are derived for the minimum photocount variances that can be achieved in direct and phase-sensitive detection. The results apply for arbitrary quantum efficiency and integration time, and they cover both homodyne and heterodyne detection in the phase-sensitive case. Particular attention is given to the regions of operation in which the photodetection-noise figures lie below the minimum values permitted by classical theory and correspond to sub-Poissonian statistics and squeezing.

Horace P. Yuen, Jeffrey H. Shapiro