A vapor–photonic integrated circuit platform based on thin film lithium niobate

A chip-scale platform that integrates alkali vapor cells with photonic integrated circuits (PICs) could enable truly deployable quantum sensors and on-chip quantum resources. Several groups have demonstrated both near-field and far-field coupling to alkali vapors using integrated waveguides, ring resonators, gratings, and advances in device design have improved vapor–PIC interaction strength while pushing these systems toward greater scalability and compactness. To date, however, essentially all such demonstrations have relied on the silicon nitride (SiN) platform.

Here we propose a new materials direction, thin-film lithium niobate (TFLN), to broaden the capabilities of vapor–PIC systems. Like SiN, TFLN offers a wide transparency window, but it additionally provides a strong electro-optic response and a large second-order nonlinearity, enabling active and nonlinear on-chip functionality beyond what is readily available in SiN. As a first step, we are developing integrated second-harmonic and electro-optic frequency-comb generation in TFLN to convert telecom-band sources to wavelengths suitable for probing potassium and rubidium transitions. This approach points toward compact, scalable vapor–PIC platforms with built-in modulation and nonlinear frequency conversion for next-generation quantum sensing and atomic photonics.