Preparation of Metrological States in Dipolar-Interacting Spin Systems

TL;DR

This paper presents a variational method to create highly sensitive quantum states in small dipolar spin systems, enabling measurements beyond classical limits despite noise and control limitations.

Contribution

It introduces a novel variational approach for generating metrological states in dipolar spin systems with limited controls and unknown positions.

Findings

States enable sensing beyond the standard quantum limit.

Generated states can resemble GHZ or Spin Squeezed States.

Sensing advantage persists under realistic noise conditions.

Abstract

Spin systems are an attractive candidate for quantum-enhanced metrology. Here we develop a variational method to generate metrological states in small dipolar-interacting ensembles with limited qubit controls and unknown spin locations. The generated states enable sensing beyond the standard quantum limit (SQL) and approaching the Heisenberg limit (HL). Depending on the circuit depth and the level of readout noise, the resulting states resemble Greenberger-Horne-Zeilinger (GHZ) states or Spin Squeezed States (SSS). Sensing beyond the SQL holds in the presence of finite spin polarization and a non-Markovian noise environment.