Long-lived Quantum State Storage Based on Coherent Mechanical Excitations

Abstract

Mechanical resonators, their capability to host ultralong-lived phonon modes, are particularly attractive for quantum state storage and as memory elements in conjunction with quantum computing and communication devices. Here, we demonstrate mechanical quantum memory based on a high-stressed silicon nitride (SiN) membrane which is sideband cooled down to its ground state. We investigate an itinerant microwave field captured, stored, and retrieved from a mechanical oscillator based on write and readout pulses that have exponential envelopes. By projecting the retrieval transfer pulse to orthogonal and damped oscillatory functions, we determine two quadrature amplitudes and yield a single point in the quadrature phase space that represents the best estimate of the mechanical resonator. The phase space distribution allows us to distinguish between coherent and thermal components and their evolution as a function of the storage time. Benefitting from the long coherence property of the SiN mechanical oscillator, we demonstrate that such mechanical quantum memory performs attractive functions with an energy decay time of T1= 15.9 s, and acquires less than one quantum noise during the Τcoh = 55.7 ms storage period. These results suggest that high-Q mechanical resonators and long coherence time phonons could be ideal candidates for the construction of microwave quantum memories