Quasinormal Mode Spectroscopy via Horizon-Brightened Quantum Optics

TL;DR

This paper introduces a quantum optical method to detect black hole quasinormal modes using two-level atoms, linking gravitational wave signals with quantum optics and providing a new perspective on black hole spectroscopy.

Contribution

It develops a novel quantum optical framework for probing black hole QNMs through atomic detectors and models the dominant QNM as a non-Hermitian cavity mode, connecting gravity and quantum optics.

Findings

QNM resonances appear as Lorentzian peaks in detector spectra

The lasing threshold depends on the QNM damping rate

Framework applies to Schwarzschild black holes and relates to photon-sphere data

Abstract

We develop a quantum optical framework for probing black hole quasinormal modes (QNMs) using two-level atoms in the spirit of the horizon-brightened acceleration radiation (HBAR) program. Starting from the QNM contribution to the Wightman function of a scalar field on a static, spherically symmetric black hole background, we derive the response function of a two-level Unruh--DeWitt detector following simple trajectories (static at fixed radius, with comments on radial free fall). The QNM sector imprints a set of Lorentzian resonances in the detector spectrum at the redshifted real parts of the QNM frequencies, with widths determined by the imaginary parts. We then treat a single dominant QNM as an effective non-Hermitian cavity mode coupled to an ensemble of driven two-level atoms, and derive a master equation of Dicke laser type. The resulting lasing threshold condition depends explicitly on the QNM damping rate, providing a direct quantum optical interpretation of the imaginary part of the QNM frequency. Specializing to the Schwarzschild geometry, we express the resonant frequencies, linewidths, and threshold in terms of photon-sphere data in the eikonal limit. We discuss several extensions and propose our framework as a unifying language connecting black hole ringdown, near-horizon conformal quantum mechanics, and quantum optics, thereby enriching the emerging program of black hole spectroscopy in the gravitational-wave era.