Absolutely Stable Spatiotemporal Order in Noisy Quantum Systems

TL;DR

This paper presents a quantum model that maintains stable spatiotemporal order despite noise, using a novel combination of measurements and feedback, with potential for experimental realization on current quantum computers.

Contribution

The authors introduce a non-unitary quantum dynamics model that achieves long-lived order resistant to perturbations, combining measurement-based feedback with classical cellular automaton principles.

Findings

Demonstrates stable order in noisy quantum systems via numerical simulations.

Shows feasibility of experimental implementation on existing quantum hardware.

Provides a new approach to preserving quantum coherence in complex systems.

Abstract

We introduce a model of non-unitary quantum dynamics that exhibits infinitely long-lived discrete spatiotemporal order robust against any unitary or dissipative perturbation. Ergodicity is evaded by combining a sequence of projective measurements with a local feedback rule that is inspired by Toom's `North-East-Center' classical cellular automaton. The measurements in question only partially collapse the wavefunction of the system, allowing some quantum coherence to persist. We demonstrate our claims using numerical simulations of a Clifford circuit in two spatial dimensions which allows access to large system sizes, and also present results for more generic dynamics on modest system sizes. We also devise explicit experimental protocols realising this dynamics using one- and two-qubit gates that are available on present-day quantum computing platforms.