Single-domain Bose condensate magnetometer achieves energy resolution per bandwidth below ℏ

Abstract

We present a magnetic sensor with energy resolution per bandwidth ER<ℏ. We show how a 87Rb single-domain spinor Bose–Einstein condensate, detected by nondestructive Faraday rotation probing, achieves single-shot low-frequency magnetic sensitivity of 72(8) fT measuring a volume V=1,091(30) μm3 for 3.5 s, and thus, ER=0.075(16)ℏ. We measure experimentally the condensate volume, spin coherence time, and readout noise and use phase space methods, backed by three-dimensional mean-field simulations, to compute the spin noise. Contributions to the spin noise include one-body and three-body losses and shearing of the projection noise distribution, due to competition of ferromagnetic contact interactions and quadratic Zeeman shifts. Nonetheless, the fully coherent nature of the single-domain, ultracold two-body interactions allows the system to escape the coherence vs. density trade-off that imposes an energy resolution limit on traditional spin precession sensors. We predict that other Bose-condensed alkalis, especially the antiferromagnetic 23Na, can further improve the energy resolution of this method.

Levitated Micromagnets in Superconducting Traps: A New Platform for Tabletop Fundamental Physics Experiments

“…Most existing magnetometers, such as SQUIDs and atomic magnetometers, satisfy the relation , a sort of practical quantum limit better known as Energy Resolution Limit (ERL) [ 17 ]. The ERL has been substantially beaten only recently by a Bose-Einstein Condensate (BEC) based magnetometer [ 18 ]. According to ref.…”