Center for Underground Physics

A superradiant state is a phase-correlated quantum state of atoms capable of

undergoing superradiance immediately without a time delay. We can prepare a

superradiant state in an optical cavity by exciting atoms in the same

superposition of the ground and excited states with a common phase angle by

using a nanohole array aperture. These correlated atoms generate

superradiance in the cavity even when the mean number of intracavity atoms is

much less than unity [1]. As an application, the superradiant state can be used

to realize the long-sought superabsorption, the opposite of superradiance, by

reversing the superradiance process in time through the phase control of the

superradiant state [2]. Another application is a photonic quantum engine,

where the atoms entering the cavity act as a heat reservoir and the photons are

an engine medium exerting radiation pressure on the cavity mirrors. Our engine

operates between a thermal state and a superradiant state of reservoir at the

same reservoir temperature. In our experiment, the engine efficiency was as

high as 98%, the highest ever achieved in quantum engines [3]. Moreover, our

superradiant lasing does not exhibit the conventional laser threshold that would

occur around unity mean photon number. We observed the coherent photon

statistics even when the mean photon number was far less than unity. [4].

Recent progresses toward a thresholdless macroscopic superradiant laser as

well as superradiant optical clock without any frequency pulling effect [5] will

also be discussed.

References

[1] Junki Kim et al., "Coherent single-atom superradiance", Science 359, 662

(2018).

[2] Daeho Yang et al., "Realization of superabsorption by time reversal of

superradiance", Nature Photonics 15, 272 (2021).

[3] Jinuk Kim et al., "A photonic quantum engine driven by superradiance",

Nature Photonics 16, 707 (2022).

[4] Seunghoon Oh et al., "Thresholdess coherence in a superradiant laser",

Light: Science and Applications 13, 239 (2024).

[5] M. Jeon et al., "Numerical analysis of a superradiance-sideband-assisted

laser with a zero frequency pulling and a narrow linewidth”,

arXiv:2408.09486[quant-ph] (2024)