Improved sensing with a single qubit

TL;DR

This paper introduces a method to enhance quantum sensing sensitivity using a single qubit by effectively simulating multi-level systems through auxiliary degrees of freedom, enabling accurate estimation of large parameters with arbitrary prior knowledge.

Contribution

It demonstrates how to use auxiliary systems and control operations to emulate multi-level spectra in a single qubit for improved Bayesian quantum metrology.

Findings

Single qubit can act as a virtual multi-level system for sensing.

Enhanced sensitivity in Bayesian, single-shot scenarios.

Ability to estimate large parameters without phase ambiguity.

Abstract

We consider quantum metrology with arbitrary prior knowledge of the parameter. We demonstrate that a single sensing two-level system can act as a virtual multi-level system that offers increased sensitivity in a Bayesian, single-shot, metrology scenario and that allows one to estimate (arbitrary) large parameter values by avoiding phase wraps. This is achieved by making use of additional degrees of freedom or auxiliary systems not participating in the sensing process. The joint system is manipulated by intermediate control operations in such a way that an effective Hamiltonian, with an arbitrary spectrum, is generated that mimics the spectrum of a multi-level system interacting with the field. We show how to use additional internal degrees of freedom of a single trapped ion to achieve a high-sensitivity magnetic field sensor for fields with arbitrary prior.