Observing the emergence of a velocity hierarchy in matter waves

• URL: http://arxiv.org/abs/2608.05241v1
• Date: Wed, 05 Aug 2026 14:24:25 GMT
• Title: Observing the emergence of a velocity hierarchy in matter waves
• Abstract summary: We demonstrate the emergence of a velocity hierarchy in a strongly interacting lattice gas.<n>These velocities are nearly close to the transition, but progressively separate as the Mott gap opens.<n>Strikingly, phase-coherence fronts propagate faster than the Lieb-Robinson velocity scale.
• Score: 4.466211773760175
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• 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.

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