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In an orchestra, one musician plays so quietly that their sound is almost inaudible in the overall chorus. In the quantum world, such 'quiet' states are called dark: their energy barely escapes, like light in a darkened room. But if there are many musicians, their mutual influence can unexpectedly awaken even the most silent one.

In the new work, physicists considered a chain of spins (quantum 'tops') with a special type of dissipation acting on neighboring sites. In such a system, there exists a single-particle dark state with zero momentum: it, like a conductor, sets the rhythm but remains in the shadows. However, with a large number of particles, this state begins to slowly fade: its decay goes as [formula:decay]1/ln(t)[/formula], where t is time. It's like watching a candle flame not go out at once but smolder for a long time, obeying a tricky law.

The most surprising thing is that the system's behavior turned out to be universal. The distribution of particles over velocities (momenta) is described by a single form depending on [formula:scaling]k√t[/formula], and the total particle density falls as [formula:density]1/(√t * ln(t))[/formula]. This resembles the pattern left on sand after the tide: no matter what the tide was like, the lines remain similar. The results were confirmed by numerical simulation, and even with weak particle interactions the picture does not change — nature seems to insist on this scenario.

Original abstract

as written by the authors arXiv:2605.16494

Open quantum systems can host dark or subradiant states whose decay is highly suppressed. While these states have been extensively studied in the few-excitation regime, their impact on the many-body dynamics remains largely unexplored. Here, we study a spin chain subject to correlated dissipation on neighboring sites, which admits a single-particle dark state at zero momentum. We show that the single-particle dark state qualitatively alters the many-body dynamics at long times, and identify its distinct universal behavior. While the zero-momentum mode is dark at the single-particle level, it decays slowly as $$1/\log t$$ as it becomes dressed by other modes through a dissipation-induced nonlinearity. We demonstrate that the momentum distribution takes a universal scaling form in $$k\sqrt{t}$$, and the total density decays as $$1/\sqrt{t}\log t$$. Our results further elucidate the origin of the conflicting results in recent works. Finally, we corroborate the analytics with matrix product state simulations and show that the same universal behavior persists for soft-core interactions, underscoring the universality of the emergent dynamics.