Reconfigurable quantum phononic circuits via piezo-acoustomechanical interactions

Phonons provide both direct and mediated interactions for quantum transduction. Augmenting these interactions with active phononic components would broaden the scope of quantum information processing functionalities. We investigate piezoelectric strain actuation of acoustomechanical interactions to design a phase shifting waveguide capable of reconfiguring a phononic circuit by tuning the speed of sound. This mechanism could be applied to a variety of acoustic materials; here we focus on the material platform of a cryogenic suspended Si phononic crystal membrane outfitted with Sc_xAl_(1-x)N piezoelectric transducers. The finite element analysis of our waveguide demonstrates ±π phase shifts for GHz frequency phonons over a length scale of 10s of μm with 10s of volts applied. We employ this phase shifting element to design a phononic quantum memory that functions by dynamically reconfiguring the coupling to a high-Q phononic cavity using interference. We optimize the classical control fields on the actuators in the memory by employing the master equation for the full open quantum system, yielding a state transfer fidelity into the cavity for an exponentially decaying pulse that approaches 90%.