Rabi Oscillations Modulated Noise Squeezing in Active Quantum Dot Ensembles

Abstract: Generation of squeezed light is usually implemented in nonlinear \c{hi}(2) or \c{hi}(3) materials. Semiconductor lasers and optical amplifiers (SOAs) also offer non-linearities but they differ from passive elements in that they add amplified spontaneous emission noise (ASE). In a semiconductor laser, squeezing to below the shot noise limit has been demonstrated. An SOA contains no cavity and it adds significant noise. Gain saturation can lead, in principle, to squeezing of the photon number quadrature to below the shot noise level but often the noise is reduced only to below the ASE level of a linear amplifier. At the same time, the noise in the phase quadrature increases according to the Heisenberg uncertainty principle. Short resonant pulses interacting with a quantum dot SOA induce coherent effects such as Rabi oscillations. Here, we demonstrate, for the first time, that Rabi oscillations cause cyclical noise squeezing which varies periodically with the excitation pulse area. The noise in the present experiments does not reach the quantum limit so we term this condition quasi squeezing. It occurs during the portions of the Rabi cycle when the quantum dots provide gain and repeats with every fourfold increase of the pulse excitation energy which amounts to a 2{\pi} increase in pulse area. In all other cases, the noise exhibits the properties of a coherent state.