Nonequilibrium-induced enhancement of dynamical quantum coherence and entanglement of spin arrays

TL;DR

This paper demonstrates that nonequilibrium conditions, induced by chemical potential gradients in nuclear spin environments, can enhance quantum coherence and entanglement in spin qubits, with potential experimental observation using ultracold ions.

Contribution

It provides an exact and analytical study of spin qubits coupled to nuclear baths beyond weak and Markovian approximations, revealing how detailed-balance breaking boosts quantum coherence and entanglement.

Findings

Nonequilibrium conditions cause rapid oscillations in populations, coherence, and entanglement.

Non-Markovian nuclear spin baths can preserve collective quantum states.

Proposed ultracold ion experiments can observe these effects.

Abstract

The random magnetic field produced by nuclear spins has long been viewed as the dominating source of decoherence in the quantum-dot based spins. Here we obtain in both exact and analytical manner the dynamics of spin qubits coupled to nuclear spin environments via the hyperfine interaction, going beyond the weak system-bath interaction and Markovian approximation. We predict that the detailed-balance breaking produced by chemical potential gradient in nuclear baths leads to the rapid oscillations of populations, quantum coherence and entanglement, which are absent in the conventional case (i.e., Overhauser noise). This is attributed to the nonequilibrium feature of the system as shown in the relation between the oscillation period and the chemical potential imbalance. Our results reveal the essentiality of nonequilibriumness with detailed-balance breaking for enhancing the dynamical coherence and entanglement of spin qubits. Moreover, our exact solution explicitly demonstrates that the non-Markovian bath comprised by nuclear spins can preserve the collective quantum state, due to the recovery of coherence. Finally, we propose an experiment using ultracold trapped ions to observe these nonequilibrium and memory effects.