Design of heterogeneously integrated lithium niobate devices for quantum frequency conversion

Nonlinear χ(2) optical materials like thin film lithium niobate have gained significant interest for their high conversion efficiencies at low pump power, offering important utility for wavelength conversion processes. However, their at-scale use in technologically-mature integrated photonic devices has been limited, due to material incompatibilities with foundry processes and long development times for new etch processes. These limitations can be addressed by heterogeneous bonding of nonlinear optical thin films to CMOS-compatible photonic chips, where optical waveguides in the CMOS chip are evanescently coupled to the nonlinear optical thin film. We present a design approach and simulated results for a heterogeneous device that uses Si3N4-TFLN hybridized optical modes to perform frequency conversion between neutral atom (780 nm) and photonic (1550 nm) qubits. In addition, we discuss the key fabrication dependencies in our material stack and provide an outlook on the generalization of this approach to other thin-film material systems.