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Emergence of Second-Order Coherence in Superfluorescence

Constanze Bach, Felix Tebbenjohanns, Christian Liedl, Philipp Schneeweiss, and Arno Rauschenbeutel

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Phys. Rev. Lett. 136, 063402 – Published 10 February, 2026

DOI: https://doi.org/10.1103/r3kg-c4x9

Abstract

We experimentally investigate the second-order quantum coherence function of a superradiant burst in a cascaded quantum system. We chirally (i.e., direction dependently) couple about 900 cesium atoms to the forward-propagating mode of an optical nanofiber. We then prepare the ensemble close to the maximally excited state, where the subsequent collective emission of a burst is known as superfluorescence. Here, we observe that second-order coherence emerges in the course of the decay. This is a clear signature of the underlying collective dynamics that is also at the origin of the superradiant burst itself. We furthermore study the dynamics of the second-order coherence function of the emission in relation to the initial average dipole moment of the ensemble. In addition, by investigating the correlation of early and late photon emission events, we obtain evidence for fundamental shot-to-shot fluctuations in the delay of the emission of the burst. Our findings thus reveal surprising similarities between superradiance in cascaded and symmetrically coupled systems, despite the fact that they are described by fundamentally different coupling Hamiltonians.

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Phys. Rev. Lett. 136, 063402– Published 10 February, 2026
  • Received 6 August 2024
  • Revised 26 November 2025
  • Accepted 16 January 2026
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