Quantum-noise reduction at frequencies up to 0.5 GHz using pulsed parametric amplification

Nonlinear optics with less than one photon

We demonstrate suppression and enhancement of spontaneous parametric down-conversion via quantum interference with two weak fields from a local oscillator (LO). Effectively, pairs of LO photons up-convert with high efficiency for appropriate phase settings, exhibiting an effective nonlinearity enhanced by at least 10 orders of magnitude. This constitutes a two-photon switch and promises to be applicable to a wide variety of quantum nonlinear optical phenomena.

Quadrature squeezing with ultrashort pulses in nonlinear-optical waveguides

Using ultrashort laser pulses, we have observed quadrature squeezing and parametric gain in quasi-phase-matched KTiOPO(4) waveguides. Using a local oscillator pulse that is 2.5 times shorter than the squeezed pulse, we observed noise reduction of 12 +/- 1% below the shot-noise level. Parametric amplification and deamplification of a coherent seed pulse have also been observed, with no indication of gain-induced diffraction.