Ultranarrow linewidth photonic-atomic laser

Lasers with high spectral purity can enable a diverse application space, including precision spectroscopy, coherent high-speed communications, physical sensing, and manipulation of quantum systems. Already, meticulous design and construction of bench Fabry-Perot cavities has made possible dramatic achievements in active laser-linewidth reduction, predominantly for optical-atomic clocks. Yet there is increasing demand for miniaturized laser systems operating with high performance in ambient environments. Here, we report a compact and robust photonic-atomic laser comprising a 2.5 cm long, 20,000 finesse, monolithic Fabry-Perot cavity integrated with a micromachined rubidium vapor cell. By leveraging the short-time frequency stability of the cavity and the long-time frequency stability of atoms, we realize an ultranarrow-linewidth laser that enables integration for extended measurements. Specifically, our laser supports a fractional-frequency stability of 1 × 10^-13 at an averaging time of 20 ms, 7 × 10^-13 at 300 s, an integrated linewidth of 25 Hz that results from thermal noise, frequency noise floor as low as 0.06 Hz²/Hz, and a passive vibration immunity as low as 10^-10/g. Our work explores hybrid laser systems with monolithic photonic and atomic packages based on physical design.