Quantum noise limited and entanglement-assisted magnetometry

TL;DR

This paper demonstrates quantum noise-limited sensitivity and entanglement-enhanced magnetometry using a large atomic ensemble, achieving sub-femtoTesla sensitivity for pulsed magnetic fields.

Contribution

It experimentally shows that EPR entanglement improves magnetometer sensitivity beyond classical limits in a large atomic ensemble.

Findings

Achieved near projection noise limited sensitivity with optimal measurement sequence.

Demonstrated EPR entanglement enhances sensitivity to pulsed magnetic fields.

Achieved sub-femtoTesla/sqrt(Hz) sensitivity with 1.5×10^12 atoms.

Abstract

We study experimentally the fundamental limits of sensitivity of an atomic radio-frequency magnetometer. First we apply an optimal sequence of state preparation, evolution, and the back-action evading measurement to achieve a nearly projection noise limited sensitivity. We furthermore experimentally demonstrate that Einstein-Podolsky-Rosen (EPR) entanglement of atoms generated by a measurement enhances the sensitivity to pulsed magnetic fields. We demonstrate this quantum limited sensing in a magnetometer utilizing a truly macroscopic ensemble of 1.5*10^12 atoms which allows us to achieve sub-femtoTesla/sqrt(Hz) sensitivity.