Cavity-Free $\Delta$-Type Coherent Population Trapping for Microwave Sensing

TL;DR

This paper demonstrates a cavity-free elta-type coherent population trapping system for microwave sensing, showing high sensitivity to microwave parameters and potential applications in compact atomic clocks and quantum sensors.

Contribution

It introduces a novel cavity-free elta configuration for CPT, with a theoretical model matching experimental results, advancing microwave control in atomic systems.

Findings

CPT resonance strongly depends on microwave power and detuning.

Theoretical density-matrix model accurately predicts experimental results.

System shows potential for compact atomic clocks and quantum sensing.

Abstract

We investigated experimentally and theoretically a cavity-free microwave field that couples the two ground states of a {\Lambda}-type atomic system, thereby forming a closed {\Delta} configuration. In this regime, the absence of cavity-imposed phase matching leads to a strong sensitivity of the ground-state coherence to the microwave field parameters. We observe that the coherent population trapping (CPT) resonance exhibits a pronounced dependence on the microwave power and detuning, resulting in measurable changes in resonance contrast, linewidth, and center frequency. To explain these effects, we develop a numerical density-matrix model in which the ground-state coherence explicitly incorporates the microwave coupling strength, capturing the essential physics of this no-phase-matching {\Delta} system. The excellent agreement between theory and experiment establishes a simple and robust framework for microwave control of cavity-free {\Delta}-type atomic systems, with direct implications for compact atomic clocks and quantum-enhanced quantum sensing platforms.