  Recent advances in photonic integrated circuits (PICs) have enabled a new
generation of "programmable many-mode interferometers" (PMMIs) realized by
cascaded Mach Zehnder Interferometers (MZIs) capable of universal
linear-optical transformations on N input-output optical modes. PMMIs serve
critical functions in photonic quantum information processing, quantum-enhanced
sensor networks, machine learning and other applications. However, PMMI
implementations reported to date rely on thermo-optic phase shifters, which
limit applications due to slow response times and high power consumption. Here,
we introduce a large-scale PMMI platform, based on a 200 mm CMOS process, that
uses aluminum nitride (AlN) piezo-optomechanical actuators coupled to silicon
nitride (SiN) waveguides, enabling low-loss propagation with phase modulation
at greater than 100 MHz in the visible to near-infrared wavelengths. Moreover,
the vanishingly low holding-power consumption of the piezo-actuators enables
these PICs to operate at cryogenic temperatures, paving the way for a fully
integrated device architecture for a range of quantum applications.
