Light Reveals Hidden Glitches in Quantum Systems express
Light from a quantum system is like a singer's voice: by the tremor, you can tell something's off with the vocal cords. Physicists have found that in the emission spectrum of a collective spin (a group of atoms behaving like a single magnet), peculiar distortions appear when the system passes through so-called exceptional points.
Such points arise when the system exchanges energy with its surroundings asymmetrically, as if one door opens easily while another sticks. As a result, the signal decay is no longer the usual exponential (a smooth decline, like tea cooling down) but gains extra ripples. These ripples leave their mark in the spectrum, like characteristic overtones in a voice.
But here's the catch: if the system has already settled down and is glowing steadily, these traces are barely visible. However, if you start it from a random state (like shaking a box of atoms), the distortions in the spectrum become pronounced. This means that by looking at the glow, you can tell whether the system is in a special phase, simply by changing how you prepare it.
Original abstract
as written by the authors arXiv:2602.01375
Non-Hermitian degeneracies of Lindblad generators (Liouvillian exceptional points) can induce non-exponential relaxation and higher-order poles in dynamical response functions. A collective spin coupled to a polarized Markovian bath exhibits an \emph{exceptional spectral phase} in which defective Liouvillian modes imprint super-Lorentzian features in frequency-resolved spectra. We compute the emission spectrum via the Liouvillian resolvent, identify symmetry-sector selection rules, and demonstrate that exceptional-point signatures are strongly state-dependent: they are suppressed in steady-state fluorescence yet become unambiguous for generic (infinite-temperature or random) initial states. Our results provide an experimentally accessible spectroscopic diagnostic of many-body Liouvillian exceptional phases and clarify when steady-state emission can (and cannot) reveal them.
Exponential decay is the most common in nature: tea cools, echoes fade, light bulbs dim. But near exceptional points, decay can become power-law — slower, with characteristic 'tails' that show up in the spectrum.