Laser modulation transfer phenomenon in a four-level heterodyne Rydberg atom system.

This paper investigates the transfer of probe or coupling light modulation interference to density matrix elements in a four-level heterodyne Rydberg system. By combining the density matrix dynamical equations with power spectral density (PSD) analysis, we derive analytical solutions to describe this phenomenon. Our results demonstrate that coherence in multi-level systems fundamentally enables this transfer mechanism, thereby increasing the system's noise floor and degrading microwave detection sensitivity.

Laser frequency stabilization method based on a ladder-type Rydberg atom electromagnetically induced transparency.

We established a theoretical model for the ladder-type EIT laser frequency stabilization method based on the analysis of the system response. By using the method of deriving the density matrix equations, we obtained the density matrix elements of the three-level system and subsequently derived the system's response function. Based on this, we revealed the complex interference mechanism of the modulated probe light in the atomic medium.

High-sensitivity and low-harmonic microwave detection using Rydberg atoms based on a loop-level structure.

We propose and investigate a Rydberg atom sensor based on a loop-level structure, which utilizes the eigenfrequencies of the energy levels as a reference. This design eliminates the need for the local oscillator (LO) electric field required in the traditional superheterodyne structure while maintaining a linear relationship between the readout signal and the microwave (MW) electric field to be measured, along with exhibiting significantly lower harmonic distortion. For experimental validation, we implemented a cesium atomic system based on the loop five-level structure.

Accurate measurement of the frequency offset of the laser based on electromagnetically induced transparency.

We propose a method using electromagnetically induced transparency (EIT) to measure the frequency offset of the laser relative to a cavity's resonance frequency, thereby reducing the laser detuning when preparing Rydberg atoms. Laser reflection by the vapor cell enables observation of two EIT peaks corresponding to the co-propagating and counter-propagating beams, and the peaks' position is related to laser detuning, allowing us to estimate the frequency offset of the probe and coupling lasers. The method reduces the measurement uncertainty compared to directly observing saturated absorption spectroscopy (SAS) and EIT, making it suitable for applications that require strict control over laser detuning.