# Optimizing Population Accumulation in Quantum States Using Microwave Spectroscopy

## TL;DR

This paper introduces an all-optical method utilizing microwave spectroscopy to efficiently prepare and monitor cold atoms in specific quantum states, achieving high population purity for quantum information applications.

## Contribution

It develops a real-time microwave spectral fitting technique to optimize population transfer and purity in cold atom quantum state preparation.

## Key findings

- Achieved up to 98% population purity in target quantum states.
- Demonstrated real-time tracking of population distribution during optical pumping.
- Identified upper limits of purity under weak optical pumping conditions.

## Abstract

We present an all-optical method for efficiently preparing cold atoms in a desired Zeeman state, either on the magnetically insensitive clock state (m_F=0) or a particular state suitable for processing or storing quantum information. By applying the theoretical fitting model to a single microwave spectrum, we can individually determine the population distribution, microwave polarization ratio, and microwave Rabi frequency. We can dynamically track the population distribution during the optical pumping process using this real-time microwave spectrum. In a steady-state condition, a simplified model, which considers resonant and off-resonant transitions, indicates that there is an upper limit to the purity under a weak optical pumping field. The population purity up to 96(2)% or 98(1)% on the desired quantum state has been achieved after optimizing the intensity and polarization of the optical pumping field. Our study provides valuable information and potential applications in precision measurement and quantum computation research.