Observation of metastability in open quantum dynamics of a solid-state system

TL;DR

This paper reports the first experimental observation of metastability in open quantum systems, specifically in a single nuclear spin in diamond, revealing long-lived states and their potential for quantum information applications.

Contribution

It provides the first direct experimental evidence of quantum metastability in discrete-time open quantum dynamics using a nuclear spin system.

Findings

Metastable polarization emerges after 60,000-250,000 measurements.

Achieved high-fidelity single-shot nuclear spin readout.

Observed spin relaxation time exceeding 10 seconds at room temperature.

Abstract

Metastability is a ubiquitous phenomenon in non-equilibrium physics and classical stochastic dynamics.It arises when the system dynamics settles in long-lived states before eventually decaying to true equilibria. Remarkably, it has been predicted that quantum metastability can also occur in continuous-time and discrete-time open quantum dynamics. However, the direct experimental observation of metastability in open quantum systems has remained elusive. Here, we experimentally observe metastability in the discrete-time evolution of a single nuclear spin in diamond, realized by sequential Ramsey interferometry measurements of a nearby nitrogen-vacancy electron spin. We demonstrate that the metastable polarization of the nuclear spin emerges at around 60,000-250,000 sequential measurements, enabling high-fidelity single-shot readout of the nuclear spin under a small magnetic field of 108.4 gauss. An ultra-long spin relaxation time of more than 10 s has been observed at room temperature. By further increasing the measurement number, the nuclear spin eventually relaxes into the maximally mixed state. Our results represent a concrete step towards uncovering non-equilibrium physics in open quantum dynamics, which is practically relevant for the utilization of metastable information in various quantum information processing tasks, such as accurate quantum operations, quantum channel discrimination and quantum error correction.