Sequential measurements for quantum-enhanced magnetometry in spin chain probes

TL;DR

This paper introduces a novel quantum sensing protocol that enhances measurement precision in spin chain probes through sequential local measurements, surpassing classical limits without requiring entanglement or complex initialization.

Contribution

The authors propose a measurement sequence approach that achieves quantum-enhanced sensitivity in many-body systems without prior entanglement or state preparation.

Findings

Precision surpasses standard quantum limit with increasing measurement sequences

Protocol reaches Heisenberg limit asymptotically

Allows remote quantum sensing without complex state initialization

Abstract

Quantum sensors outperform their classical counterparts in their estimation precision, given the same amount of resources. So far, quantum-enhanced sensitivity has been achieved by exploiting the superposition principle. This enhancement has been obtained for particular forms of entangled states, adaptive measurement basis change, critical many-body systems, and steady-state of periodically driven systems. Here, we introduce a different approach to obtain quantum-enhanced sensitivity in a many-body probe through utilizing the nature of quantum measurement and its subsequent wave-function collapse without demanding prior entanglement. Our protocol consists of a sequence of local measurements, without re-initialization, performed regularly during the evolution of a many-body probe. As the number of sequences increases, the sensing precision is enhanced beyond the standard limit, reaching the Heisenberg bound asymptotically. The benefits of the protocol are multi-fold as it uses a product initial state and avoids complex initialization (e.g. prior entangled states or critical ground states) and allows for remote quantum sensing.