  We show that piezoelectric strain actuation of acoustomechanical interactions
can produce large phase velocity changes in an existing quantum phononic
platform: aluminum nitride on suspended silicon. Using finite element analysis,
we demonstrate a piezo-acoustomechanical phase shifter waveguide capable of
producing +/- pi phase shifts for GHz frequency phonons in 10s of microns with
10s of volts applied. Then, using the phase shifter as a building block, we
demonstrate several phononic integrated circuit elements useful for quantum
information processing. In particular, we show how to construct programmable
multi-mode interferometers for linear phononic processing and a dynamically
reconfigurable phononic memory that can switch between an ultra-long-lifetime
state and a state strongly coupled to its bus waveguide. From the master
equation for the full open quantum system of the reconfigurable phononic
memory, we show that it is possible to perform "read" and "write" operations
with over 90% quantum state transfer fidelity for an exponentially decaying
pulse.
