Observing the emergence of a velocity hierarchy in matter waves

Abstract:Classical waves in dispersive media naturally exhibit distinct phase and group velocities. Whether an analogous separation of velocities can emerge in matter waves under strong many-body interactions has remained experimentally unexplored. Here, we demonstrate the emergence of a velocity hierarchy in a strongly interacting lattice gas. Using quench spectroscopy together with time-resolved correlation measurements, we independently determine the sound, group, and phase velocities across the superfluid-to-Mott-insulator transition. These velocities are nearly degenerate close to the transition, but progressively separate as the Mott gap opens and the quasiparticle dispersion acquires a massive relativistic-like form. Strikingly, phase-coherence fronts propagate faster than the Lieb-Robinson velocity scale while remaining fully consistent with locality. The measured velocities satisfy a relativistic-like invariance relation in the insulating regime. Our results establish propagation-velocity hierarchies as emergent signatures of strongly correlated quantum dynamics.

Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

arXiv:2608.05241 [cond-mat.quant-gas]

(or arXiv:2608.05241v1 [cond-mat.quant-gas] for this version)

https://doi.org/10.48550/arXiv.2608.05241 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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