Piezo-optomechanics in lithium niobate on silicon-on-insulator for microwave-to-optics conversion

Cryogenic microwave qubits are globally pursued to build a compelling quantum technology. Major efforts are underway to scale up these processors, inching closer to useful tasks beyond the reach of classical technology. However, it is currently infeasible to connect the qubits well beyond a single refrigerator, limiting their use outside the laboratory. Microwave-to-optics converters are uniquely placed to tackle this challenge. One of the leading approaches exploits electro-opto-mechanics, but even cutting-edge systems suffer from excessive dissipated energy per qubit that is converted between microwaves and optics. This dissipated energy sets an upper bound on the quantum communication rate in a severely power-constrained cryo-environment. Here, we take first steps to greatly reduce this dissipated energy by combining a strongly piezoelectric material - lithium niobate (LN) - with a leading optomechanics and photonics platform - silicon-on-insulator (SOI). This hybrid LN-on-SOI platform leverages the best properties of both materials. We observe efficient piezo- and opto-mechanical interactions involving tightly confined GHz mechanics, establishing an intriguing path towards low-energy conversion between microwaves and optics.