State preparation and tomography of a nanomechanical resonator with fast light pulses

Pulsed optomechanical measurements enable squeezing, non-classical 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 which limit the conditional state width to 58xzpf, and show how decoherence causes the state to grow in time.