Dispersive detection of radio-frequency dressed states

TL;DR

This paper presents a dispersive detection method for alkali atoms in radio-frequency dressed states, enabling robust, low-noise measurements of atomic populations and differences, with potential applications in quantum sensing and atomic clocks.

Contribution

The authors introduce a novel dispersive detection technique using polarisation homodyning for dressed atomic states, improving noise robustness and enabling simultaneous measurement of multiple states.

Findings

Achieved phase-locked detection oscillating at twice the dressing frequency.

Demonstrated simultaneous detection of two optical frequencies for population difference measurement.

Potential for quantum noise limited measurements and spin squeezing.

Abstract

We introduce a method to dispersively detect alkali atoms in radio-frequency dressed states. In particular, we use dressed detection to measure populations and population differences of atoms prepared in their clock states. Linear birefringence of the atomic medium enables atom number detection via polarisation homodyning, a form of common path interferometry. In order to achieve low technical noise levels, we perform optical sideband detection after adiabatic transformation of bare states into dressed states. The balanced homodyne signal then oscillates independently of field fluctuations at twice the dressing frequency, thus allowing for robust, phase-locked detection that circumvents low-frequency noise. Using probe pulses of two optical frequencies, we can detect both clock states simultaneously and obtain population difference as well as the total atom number. The scheme also allows for difference measurements by direct subtraction of the homodyne signals at the balanced detector, which should technically enable quantum noise limited measurements with prospects for the preparation of spin squeezed states. The method extends to other Zeeman sublevels and can be employed in a range of atomic clock schemes, atom interferometers, and other experiments using dressed atoms.