Quantum-enhanced sensing of displacements and electric fields with large trapped-ion crystals

TL;DR

This paper demonstrates a quantum-enhanced sensor using a large trapped-ion crystal to detect weak displacements and electric fields with sensitivity surpassing classical limits by leveraging entanglement and many-body control techniques.

Contribution

The authors realize a large-scale quantum sensor employing entanglement between collective spin and vibrational modes in a 150-ion crystal, achieving quantum advantage in sensing.

Findings

Quantum enhanced sensitivity of 8.8 dB below SQL for displacements

Electric field measurement sensitivity of 240 nV/m in 1 second

Utilization of many-body echo to suppress thermal noise

Abstract

Developing the isolation and control of ultracold atomic systems to the level of single quanta has led to significant advances in quantum sensing, yet demonstrating a quantum advantage in real world applications by harnessing entanglement remains a core task. Here, we realize a many-body quantum-enhanced sensor to detect weak displacements and electric fields using a large crystal of $\sim 150$ trapped ions. The center of mass vibrational mode of the crystal serves as high-Q mechanical oscillator and the collective electronic spin as the measurement device. By entangling the oscillator and the collective spin before the displacement is applied and by controlling the coherent dynamics via a many-body echo we are able to utilize the delicate spin-motion entanglement to map the displacement into a spin rotation such that we avoid quantum back-action and cancel detrimental thermal noise. We report quantum enhanced sensitivity to displacements of $8.8 \pm 0.4~$dB below the standard quantum limit and a sensitivity for measuring electric fields of $240\pm10~\mathrm{nV}\mathrm{m}^{-1}$ in $1$ second ($240~\mathrm{nV}\mathrm{m}^{-1}/\sqrt{\mathrm{Hz}}$).