Freiburg 2024 – scientific programme

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A: Fachverband Atomphysik

A 13: Trapping and Cooling of Atoms (joint session Q/A)

A 13.1: Invited Talk

Tuesday, March 12, 2024, 11:00–11:30, HS 1221

Continuous lasing and pinning of the dressed cavity resonance with strongly-coupled ⁸⁸Sr atoms in a ring cavity — •Vera Schäfer — JILA, University of Colorado, Boulder, USA — Max Planck Institute for Nuclear Physics, Heidelberg, Germany

Superradiant lasers are a promising path for realising a narrow-linewidth, high-bandwidth active frequency reference. They shift the phase memory from the optical cavity, which is subject to technical and thermal vibration noise, to an ultra-narrow optical atomic transition of an ensemble of cold atoms trapped inside the cavity. Our previous demonstration of pulsed superradiance on the mHz transition in ⁸⁷Sr achieved a fractional Allan deviation of 6.7*10⁻¹⁶ at 1s of averaging. Moving towards continuous-wave superradiance promises to further improve the short-term frequency stability by orders of magnitude. A key challenge in realizing a cw superradiant laser is the continuous supply of cold atoms into a cavity, while staying in the collective strong coupling regime.

We demonstrate continuous loading and transport of cold ⁸⁸Sr atoms inside a ring cavity, after several stages of laser cooling and slowing. We further describe the emergence of zones of collective continuous lasing of the atoms on the 7.5kHz transition, 7x narrower than the cavity linewidth, and pumped by the cooling lasers via inversion of the motional states. The lasing is supported by self-regulation of the number of atoms inside the cavity that pins the dressed cavity frequency to a fixed value over >2MHz of raw applied cavity frequency. In the process up to 80% of the original atoms are expelled from the cavity.

Keywords: superradiance; self-organisation; ultracold atoms; continuous cold-atom experiments