Steady-State Superradiant Lasing with Fully Collective Dynamics*

Optical lattice atomic clocks are some of the most celebrated modern sensing devices in physics but are typically operated in a passive modality. An active atomic clock could increase the precision and deployability of current state-of-the-art clocks by replacing the reference laser with phase-stable light intrinsically generated in the system, i.e., a superradiant laser on the clock transition. However, experimental realization of a continuous-wave active atomic clock has so far been elusive primarily due to heating associated with spontaneously emitted photons during the repumping process. Here, we propose a new type of superradiant laser that overcomes the heating problem by replacing the single-particle repumping process by a collective pump mediated by an axillary optical resonator. In this way, the atoms may be pumped while always remaining cooled in the Lamb-Dicke regime. While it has been shown that fully collective superradiant lasing models with two-level systems do not possess a generic lasing threshold, we demonstrate that this restriction is overcome by including an additional ground state. An additional ground state enables the collective pumping and collective emission to be performed on different transitions. This allows for a class of SU(3) [instead of SU(2)] rotations where the collective dipole on the lasing transition can grow to a macroscopic length, and it is thereby possible to achieve steady-state superradiant lasing over a large realizable parameter space. This model exhibits properties such as a reliable source of ultracoherent light and a fully collective superradiant lasing mechanism that can survive the effects of single-particle decoherence.