State Preparation and Tomography of a Nanomechanical Resonator with Fast Light Pulses

Pulsed optomechanical measurements enable squeezing, nonclassical state creation, and backaction-free sensing. We demonstrate pulsed measurement of a cryogenic nanomechanical resonator with record precision close to the quantum regime. We use these to prepare thermally squeezed and purified conditional mechanical states, and to perform full state tomography. These demonstrations exploit large vacuum optomechanical coupling in a nanophotonic cavity to reach a single-pulse imprecision of 9 times the mechanical zero-point amplitude xzpf. We study the effect of other mechanical modes that limit the conditional state width to 58xzpf, and show how decoherence causes the state to grow in time.peerReviewe

Quadrature-Averaged Homodyne Detection for Estimating Cavity Parameters

Balanced homodyne interferometry is a well-known detection technique that allows for sensitive characterization of light fields. Conventionally a homodyne interferometer is operated by locking the relative phase of a reference beam to the signal beam by means of an active feedback loop. A less often used method is to perform a slow continuous modulation of the reference beam arm length that corresponds to averaging all relative phases during the measurement. Here we show theoretically and experimentally that this quadrature averaging can be advantageous in estimating the parameters of a resonant optical cavity. We demonstrate that the averaging turns the transduction function, from cavity frequency fluctuations into the interferometer signal, into a simple function of the laser detuning that, notably, does not depend on the parameters of possible nonresonant channels present in the system. The method needs no active feedback and gives results that are easy to interpret. Moreover, the phase-averaged measurement allows characterization of the absolute magnitude of a cavity frequency modulation.peerReviewe