Lifetime and Coherence Measurements of an Optomechanical Quantum Memory

Recent experiments have achieved quantum control of so-called nanobeam optomechanical crystals, which possess engineered mechanical resonances in the Gigahertz regime that can be addressed optically from the conventional telecom band. Here we discuss the prospects of such nanobeams with ultra-long lived mechanical modes to act as optical quantum memories. We demonstrate the heralded preparation of a single phonon Fock state which can be stored up to 2 ms while preserving the non-classicality. We further study the coherence of the memory using a superposition state of vacuum with a Fock state and find a quantum coherence time of 15 microseconds. Measurements of the mechanical frequency noise in the classical regime show a clear power dependence, allowing us to reach coherence times exceeding 100 microseconds. The protocol used in these experiments is directly applicable to existing quantum repeater architectures.