Collectively enhanced Ramsey readout by cavity sub- to superradiant transition

TL;DR

This paper experimentally demonstrates a novel collective atomic readout method using a cavity-induced sub- to superradiant transition, enhancing speed and sensitivity in quantum sensing applications.

Contribution

It introduces a new approach to atomic state readout leveraging the sub- to superradiant transition in cavity-coupled atoms, enabling fast, simple, and sensitive measurements.

Findings

Confirmed the superradiant threshold for narrow optical transitions.

Utilized subradiant states during Ramsey sequences to improve readout.

Achieved multiple Ramsey sequences with minimal heating.

Abstract

When an inverted ensemble of atoms is tightly packed on the scale of its emission wavelength or when the atoms are collectively strongly coupled to a single cavity mode, their dipoles will align and decay rapidly via a superradiant burst. However, a spread-out dipole phase distribution theory predicts a required minimum threshold of atomic excitation for superradiance to occur. Here we experimentally confirm this predicted threshold for superradiant emission on a narrow optical transition when exciting the atoms transversely and show how to take advantage of the resulting sub- to superradiant transition. A $\pi/2$-pulse places the atoms in a subradiant state, protected from collective cavity decay, which we exploit during the free evolution period in a corresponding Ramsey pulse sequence. The final excited state population is read out via superradiant emission from the inverted atomic ensemble after a second $\pi/2$-pulse, and with minimal heating this allows for multiple Ramsey sequences within one experimental cycle. Our scheme is a fundamentally new approach to atomic state readout characterized by its speed, simplicity, and high sensitivity. It demonstrates the potential of sensors using collective effects in cavity-coupled quantum emitters.