Observing weakly broken conservation laws in a dipolar Rydberg quantum spin chain

Integrable quantum many-body systems host families of extensive conservation laws, some of which are fragile: even infinitesimal perturbations can qualitatively alter their dynamical constraints. Here we show that this fragility leaves a clear experimental fingerprint in a one-dimensional quantum spin chain of as few as 14 Rydberg atoms. Weak integrability breaking from interatomic dipolar couplings is directly detectable within experimentally accessible times in the dynamics of non-local observables. In particular, magnetization fluctuations are highly sensitive to the breaking of fragile conservation laws and exhibit anomalous growth, which we observe experimentally; similar signatures appear in a semilocal string observable. Numerical simulations on substantially longer chains and a simplified classical stochastic model reproduce those features. We establish non-local observables as a sensitive probe of fragile conservation laws in quantum spin chains and Rydberg-atom arrays as a platform to test perturbative descriptions of quantum many-body dynamics with weak integrability breaking.

💡 Research Summary

In this work the authors experimentally and theoretically investigate how weak integrability breaking manifests itself in a small, controllable quantum many‑body system. The platform consists of a one‑dimensional array of fourteen 87Rb atoms trapped in optical tweezers with a uniform spacing of 10.8 µm. Two long‑lived Rydberg states, |↑⟩ = |60S₁/₂,m_J = +½⟩ and |↓⟩ = |60P₁/₂,m_J = −½⟩, encode an effective spin‑½ degree of freedom on each site. The resonant dipole‑dipole interaction gives rise to a dipolar XX Hamiltonian

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