We study the balanced-heterodyne detection of optical squeezing, for which the corresponding spectral density of
the photocurrent fluctuations produced at the output of the photo-detector is calculated as the Fourier transform
of their autocorrelation function. We show that, for maximal signal-to-noise ratio enhancement by use of squeezed
states of light, an optical signal to be measured in this scheme must be carried in the squeezed quadrature of
the carrier field. We discuss how this scheme may be exploited in gravitational-wave searching.
Experimental observation of the conservation of orbital angular momentum in spontaneous parametric down-conversion
has been theoretically attributed to phase-matching, transfer of plane-wave spectrum from pump
beam to down-converted beams. However, according to quantum mechanics, the conservation of angular momentum
arises from rotational symmetry of the Hamiltonian describing the studied physical process. Recently,
experimental evidence has been found which shows that non-conservation of orbital angular momentum can
occur in spontaneous parametric down-conversion due to rotational asymmetry of the Hamiltonian. In this
paper, we theoretically show that all reported experimental results of conservation of orbital angular momentum
in spontaneous parametric down-conversion are determined only by the Hamiltonian symmetry, and not
by phase matching, transfer of plane-wave spectrum.
We investigate experimentally the number and phase quantum noises of the light emitted by an ultrastable nondegenerate optical parametric oscillator (OPO) above threshold. Strong intensity correlations at the photon level -- number-difference squeezing or twin beams -- have already been observed by several groups. We have recently observed the twin-beam interference of a classically phase-locked OPO and have shown that the phase-difference is antisqueezed, as expected from the number-phase Heisenberg (in)equality. In this paper we describe the realization of a stable classical measurement of the joint quadratures of an OPO, as part of our ongoing effort to generate ultrastable EPR light beams simultaneously squeezed in number difference and phase sum.
We report the realization of a classically phase-locked source of quantum twin beams. Theoretical work by Reid and Drummond, and more recently by van Loock and Braunstein, predicts that such a source is adequate for creating bipartite and multipartite continuous-variable entanglement. The source is a type-II optical parametric oscillator (OPO) above threshold. Its exceptional frequency and intensity stability is derived from careful design and from three servo loops. The OPO can stably emit on the frequency-degenerate mode, pumped a few percent above the threshold. We observe a preliminary number-difference squeezing of 5.5 dB (6.4 dB inferred) at 200 kHz. In order to enable future EPR measurements, the signal and idler fields must also be classically phase-locked: we measure a signal-idler-frequency-difference linewidth smaller than 300 Hz for our OPO.