Chopped nonlinear magneto-optic rotation: a technique for precision measurements

TL;DR

This paper introduces a chopped nonlinear magneto-optic rotation (NMOR) technique that enhances magnetic field measurement precision by resonantly detecting atomic precession, achieving high sensitivity in a paraffin-coated Cs vapor cell.

Contribution

The paper presents a novel chopped-NMOR method that improves magnetic field measurement sensitivity using resonant laser modulation and atomic precession detection.

Findings

Achieved a linewidth of 85 μG in the rotation signal.

Demonstrated a sensitivity of 0.15 nG/√Hz.

Showed potential for atomic electric-dipole moment measurements.

Abstract

We have developed a technique for precise measurement of small magnetic fields using nonlinear magneto-optic rotation (NMOR). The technique relies on the resonant laser beam being chopped. During the on time, the atoms are optically pumped into an aligned ground state ($\Delta m=2$ coherence). During the off time, they freely precess around the magnetic field at the Larmor frequency. If the on-off modulation frequency matches (twice) the Larmor precession frequency, the rotation is resonantly enhanced in every cycle, thereby making the process like a repeated Ramsey measurement of the Larmor frequency. We study chopped-NMOR in a paraffin-coated Cs vapor cell. The out-of-phase demodulated rotation shows a Lorentzian peak of linewidth 85 $\mu$G, corresponding to a sensitivity of 0.15 nG/$\sqrt{{\rm Hz}}$. We discuss the potential of this technique for the measurement of an atomic electric-dipole moment.