Many-body gap protection against Doppler dephasing and continuous lasing between momentum states in a strontium cavity-QED system*

We present two recent observations in our strontium cavity QED system [1]: continuous lasing between momentum states [2] and many-body gap protection against Doppler dephasing on an optical transition [3].  Firstly, we observe continuous-wave lasing from laser-cooled 88Sr atoms continuously loaded into a high finesse ring cavity.  The lasing is truly continuous, lasting for hours and limited only by the experiment’s technical stability. The lasing arises from a collective recoil induced resonance between ground momentum states and is also related to, but distinct from, spatial self-organization phase transitions. Unexpectedly, the observed lasing frequency is 120-times less sensitive to changes in the bare optical cavity frequency, due to a lasing-induced atomic loss mechanism that self-consistently stabilizes the dressed cavity-mode frequency. This work demonstrates a path toward continuous cavity-QED quantum simulation experiments and future continuous narrow linewidth superradiant lasers. Secondly, we observe the suppression of Doppler dephasing on a narrow optical transition in strontium that arises from the emergence of a many-body energy gap generated when the atoms exchange photons via the cavity.  This offers an alternative to Lamb-Dicke or Mössbauer-like confinement for quantum sensing using clocks and clock-atom matterwave interferometers [3, 4], searches for new physics, and exploration of many-body physics.

[1] J. R. K. Cline, V. M. Schäfer, Z. Niu, et al. Phys. Rev. Lett. 134, 013403

[2] V. M. Schäfer, Z. Niu, J. R. K. Cline, et al. Nature Physics in press, arXiv:2405.20952 (2024).

[3] Z. Niu, V. M. Schäfer, H. Zhang, et al. arXiv:2409.16265 (2024).

[4] C. Luo, H. Zhang, V. P. W. Koh, et al. Science 2024, 384 (6695), 551–556