Pulsed excitation dynamics of an optomechanical crystal resonator near its quantum ground-state of motion

Abstract

Using pulsed optical excitation and read-out along with single-phonon-counting techniques, we measure the transient backaction, heating, and damping dynamics of a nanoscale silicon optomechanical crystal cavity mounted in a dilution refrigerator at a base temperature of T_f ≈ 11  mK. In addition to observing a slow (approximately 740-ns) turn-on time for the optical-absorption-induced hot-phonon bath, we measure for the 5.6-GHz “breathing” acoustic mode of the cavity an initial phonon occupancy as low as ⟨n⟩ = 0.021±0.007 (mode temperature T_(min) ≈ 70  mK) and an intrinsic mechanical decay rate of γ_0 = 328±14  Hz (Q_m ≈ 1.7×10^7). These measurements demonstrate the feasibility of using short pulsed measurements for a variety of quantum optomechanical applications despite the presence of steady-state optical heating.