Observation of Hilbert space fragmentation and fractonic excitations in 2D

Daniel Adler, David Wei, Melissa Will, Kritsana Srakaew, Suchita Agrawal, Pascal Weckesser, Roderich Moessner, Frank Pollmann, Immanuel Bloch and Johannes Zeiher ()
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Daniel Adler: Max-Planck-Institut für Quantenoptik
David Wei: Max-Planck-Institut für Quantenoptik
Melissa Will: Munich Center for Quantum Science and Technology (MCQST)
Kritsana Srakaew: Max-Planck-Institut für Quantenoptik
Suchita Agrawal: Max-Planck-Institut für Quantenoptik
Pascal Weckesser: Max-Planck-Institut für Quantenoptik
Roderich Moessner: Max-Planck-Institut für Physik komplexer Systeme
Frank Pollmann: Munich Center for Quantum Science and Technology (MCQST)
Immanuel Bloch: Max-Planck-Institut für Quantenoptik
Johannes Zeiher: Max-Planck-Institut für Quantenoptik

Nature, 2024, vol. 636, issue 8041, 80-85

Abstract: Abstract The relaxation behaviour of isolated quantum systems taken out of equilibrium is among the most intriguing questions in many-body physics1. Quantum systems out of equilibrium typically relax to thermal equilibrium states by scrambling local information and building up entanglement entropy. However, kinetic constraints in the Hamiltonian can lead to a breakdown of this fundamental paradigm owing to a fragmentation of the underlying Hilbert space into dynamically decoupled subsectors in which thermalization can be strongly suppressed2–5. Here we experimentally observe Hilbert space fragmentation in a two-dimensional tilted Bose–Hubbard model. Using quantum gas microscopy, we engineer a wide variety of initial states and find a rich set of manifestations of Hilbert space fragmentation involving bulk states, interfaces and defects, that is, two-, one- and zero-dimensional objects. Specifically, uniform initial states with equal particle number and energy differ strikingly in their relaxation dynamics. Inserting controlled defects on top of a global, non-thermalizing chequerboard state, we observe highly anisotropic, subdimensional dynamics, an immediate signature of their fractonic nature6–9. An interface between localized and thermalizing states in turn shows dynamics depending on its orientation. Our results mark the observation of Hilbert space fragmentation beyond one dimension, as well as the concomitant direct observation of fractons, and pave the way for in-depth studies of microscopic transport phenomena in constrained systems.

Date: 2024
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DOI: 10.1038/s41586-024-08188-0

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