Spectroscopic readout of chiral photonic topology in a single-cavity spin-orbit-coupled Bose-Einstein condensate

TL;DR

This paper introduces a spectroscopic method to detect chiral photonic topological phases in a single cavity with a spin-orbit-coupled Bose-Einstein condensate, linking spectral data to topological invariants without bulk-band tomography.

Contribution

It develops a novel spectroscopic framework that directly measures topological properties in a driven cavity-QED system, connecting noise spectra to geometric and non-Hermitian topology.

Findings

Spectral density reveals trivial and topological phases through Dirac-like modes and spectral ridges.

Reversal of dissipation imbalance induces topological spectral features and chiral transport.

Identification of exceptional points and gain-loss bifurcations in the complex spectrum.

Abstract

Topological photonic phases are typically identified through band reconstruction, steady-state transmission, or real-space imaging of edge modes. In this work, we present a framework for spectroscopic readout of chiral photonic topology in a single driven optical cavity containing a spin-orbit-coupled Bose-Einstein condensate. We demonstrate that the cavity transmission power spectral density provides a direct and measurable proxy for a momentum- and frequency-resolved photonic Chern marker, enabling topological characteristics to be inferred from spectral data without the need for bulk-band tomography. In the loss-dominated regime, where cavity decay exceeds atomic dissipation, the power spectral density exhibits Dirac-like gapped hybrid modes with a vanishing Chern marker, indicating a trivial phase. When the dissipation imbalance is reversed, a bright, gap-spanning spectral ridge emerges, co-localized with peaks in both the Chern marker and Berry curvature. The complex spectrum reveals parity-time symmetric coalescences and gain-loss bifurcations, marking exceptional points and enabling chiral, gap-traversing transport. By linking noise spectroscopy to geometric and non-Hermitian topology in a minimal cavity-QED architecture, this work provides a framework for spectroscopic detection of topological order in driven quantum systems. This approach offers a pathway to compact, tunable topological photonics across a broad range of light-matter platforms, providing a method for the study and control of topological phases in hybrid quantum systems.