Fock space prethermalization and time-crystalline order on a quantum processor

TL;DR

This paper introduces Fock space prethermalization (FSP), a disorder-free mechanism that suppresses heating in driven quantum systems, enabling persistent time-crystalline order on a 72-qubit superconducting quantum processor.

Contribution

The authors propose and experimentally demonstrate Fock space prethermalization as a new disorder-free method to prolong thermalization times and stabilize nonequilibrium quantum phases.

Findings

FSP divides Fock space into sparse sub-networks, delaying thermalization.

Time-crystalline order persists over 120 cycles in a 72-qubit system.

Finite-size analysis links dynamics to Floquet eigenstructure.

Abstract

Periodically driven quantum many-body systems exhibit a wide variety of exotic nonequilibrium phenomena and provide a promising pathway for quantum applications. A fundamental challenge for stabilizing and harnessing these highly entangled states of matter is system heating by energy absorption from the drive. Here, we propose and demonstrate a disorder-free mechanism, dubbed Fock space prethermalization (FSP), to suppress heating. This mechanism divides the Fock-space network into linearly many sparse sub-networks, thereby prolonging the thermalization timescale even for initial states at high energy densities. Using 72 superconducting qubits, we observe an FSP-based time-crystalline order that persists over 120 cycles for generic initial Fock states. The underlying kinetic constraint of approximately conserved domain wall (DW) numbers is identified by measuring site-resolved correlators. Further, we perform finite-size scaling analysis for DW and Fock-space dynamics by varying system sizes, which reveals size-independent regimes for FSP-thermalization crossover and links the dynamical behaviors to the eigenstructure of the Floquet unitary. Our work establishes FSP as a robust mechanism for breaking ergodicity, and paves the way for exploring novel nonequilibrium quantum matter and its applications.