In situ magnetic-field stabilization for quantum-gas experiments

TL;DR

This paper introduces an in situ, minimally-destructive method using atomic weak measurements and a Kalman filter to accurately measure and stabilize magnetic fields in ultracold-atom experiments, overcoming limitations of traditional sensors.

Contribution

The authors develop a novel in situ atomic magnetometry technique combined with Kalman filtering for magnetic field stabilization in quantum-gas experiments, improving accuracy and reducing perturbations.

Findings

Successfully stabilized magnetic fields with minimal atom loss.

Eliminated long-term ambient magnetic field drift.

Achieved shot-to-shot variability of about 2 nT.

Abstract

We demonstrate a minimally-destructive in situ technique for measuring and stabilizing slowly-drifting magnetic fields in ultracold-atom experiments. While conventional magnetic-field sensors such as Hall, giant magnetoresistive, or fluxgate-based devices are broadly used, their accuracy, precision and dynamic range can be limited. In addition, these sensors are typically positioned at least several centimeters away from the in-vacuum atomic system, as their operation creates perturbing magnetic fields, and their placement is limited by geometric constraints imposed by the vacuum system. We overcome these issues by using the atomic system itself as a built-in magnetometer. To that end, we employ a pair of weak measurements to determine the Zeeman splitting -- and thereby the magnetic field -- of a magnetically sensitive atomic transition. We provide closed-form expressions quantifying the trade-offs between measurement noise, dynamic range, and atom loss. This procedure is demonstrated with ultracold Rb-87, weakly measured using partial-transfer absorption imaging. We then incorporate a Kalman filter to stabilize the magnetic field; this eliminated long-term drift in the ambient field (as high as ~70 nT/hr) in exchange for a modest increase in shot-to-shot variability from 1.8(2) nT to 2.0(2) nT.