Sub-Hertz resonance by weak measurement

TL;DR

This paper introduces a weak measurement-enhanced spectroscopy method that significantly narrows resonance linewidths and improves magnetic field sensing sensitivity in atomic vapor cells, advancing precision measurement techniques.

Contribution

The study demonstrates a novel WM-based spectroscopy technique achieving 0.1 Hz resonance narrowing and high-sensitivity magnetic field detection, extending WM to non-Hermitian Hamiltonians.

Findings

Resonance linewidth narrowed to 0.1 Hz in room-temperature vapor.

Magnetic field sensitivity of 7 fT/√Hz near DC.

Extension of WM framework to non-Hermitian Hamiltonians.

Abstract

Weak measurement (WM) with state pre- and post-selection can amplify otherwise undetectable small signals and thus promise great potentials in precision measurements. Although frequency measurements offer the hitherto highest precision owing to stable narrow atomic transitions, it remains a long-standing interest to develop new schemes to further escalate their performance. Here, we propose and demonstrate a WM-enhanced spectroscopy technique which is capable of narrowing the resonance to 0.1 Hz in a room-temperature atomic vapor cell. Potential of this technique for precision measurement is demonstrated through weak magnetic field sensing. By judiciously pre- and post-selecting frequency-modulated input and output optical states in a nearly-orthogonal manner, a sensitivity of $\text{7 fT/}\sqrt{\text{Hz}}$ near DC is achieved, using only one laser beam of $\text{7 }\text{\mu W}$ power. Additionally, our results extend the WM framework to a non-Hermitian Hamiltonian, and shed new light in metrology and bio-magnetic field sensing applications.