On the relationship between noise squeezing and Rabi oscillations in active quantum dot ensembles

TL;DR

This paper explores how Rabi oscillations in room-temperature quantum-dot SOAs induce cyclical noise modifications, leading to states with squeezing below the vacuum level and revealing complex quantum state behaviors over varying pulse energies.

Contribution

It demonstrates the periodic influence of Rabi oscillations on noise properties and quantum states in quantum-dot SOAs, including the observation of non-Gaussian states.

Findings

Squeezed thermal states observed at specific pulse areas.

Periodic noise modification correlates with 2pi pulse area changes.

Detection of non-Gaussian, potentially Schrödinger cat-like states.

Abstract

Squeezed light is usually generated using passive nonlinear materials. Semiconductor lasers and optical amplifiers (SOAs) also offer nonlinearities but they differ in that they add amplified spontaneous emission (ASE). Squeezing to below the vacuum level has been demonstrated in a semiconductor laser, and gain saturation in SOAs can likewise reduce photon-number fluctuations to, and in some cases below, the vacuum limit. Here, we demonstrate that Rabi oscillations in room-temperature quantum-dot SOAs, induced by short resonant pulses, cause cyclical noise modification that repeat with every change of 2pi in pulse area, corresponding to a fourfold increase in excitation pulse energy. Homodyne measurements reveal in those cases elliptical Wigner functions corresponding to squeezed thermal states and in certain regimes, the state is squeezed to below the vacuum level. At other pulse areas, the Wigner functions are circular representing thermal coherent states. This periodic behavior persists over two orders of magnitude in input pulse energy, spanning several 2pi cycles. Under specific bias and excitation conditions, we further observe a non-Gaussian Wigner function featuring two bright lobes. Although its precise nature remains unresolved, this structure may be consistent with a Schrodinger cat - like state whose accompanying negativity is suppressed due to an approximately 10 dB optical output loss. Notably, the emergence of this non-Gaussian state is itself periodic in excitation pulse energy.