Full integration of alkali vapors and photonic circuits for nonlinear and quantum optics

We present a hybrid platform that integrates versatile and compact nanophotonic chips with the simplicity and accessibility of alkali atomic vapor. This approach, facilitated by reliable processes based on chemical-mechanical polishing (CMP) and anodic bonding to micromachined glass cells, enables the employment of a rubidium (Rb) pill source, allowing for on-demand Rb vapor generation with tunable density without requiring changes in operating temperature. This approach offers both flexibility and scalability for various applications. We experimentally demonstrate Rb D-line spectroscopy across waveguides of varying lengths. We further observe normal mode splitting in microcavities, confirming strong coupling in the cavity quantum electrodynamics (cavity QED) regime. Moreover, we demonstrate operation at temperatures approaching 300^oC, significantly exceeding that shown in previous epoxy-bonded devices.

However, a key challenge in this system is the high reactivity of Rb, which degrades photonic quality over time. This issue is particularly critical when investigating serpentine waveguides, designed for extended interaction lengths, and slotted microring resonators, which confine optical fields in their air gaps. To mitigate these effects, we implement several strategies. Elevating the base temperature reduces Rb adhesion, high-power laser atomic desorption via off-resonant azimuthal modes in microring resonators prevents buildup, and atomic layer deposition (ALD) of alumina protects photonic surfaces from corrosion. Looking forward, we aim to refine Rb vapor control to the beam source level, enabling precise manipulation of atomic interactions with nanophotonic structures. This work establishes a robust atomic-photonic platform for nonlinear optics and cavity QED explorations and applications.