Quantum-enhanced measurement schemes promise sensitivities beyond the shot noise limit, but their practical implementation in atomic systems has long been hindered by optical loss and decoherence. In particular, squeezed states of light—one of the most accessible quantum resources—are extremely fragile when interacting with resonant atomic media, where absorption and scattering rapidly degrade their noise suppression advantage.
In this work, researchers report the first realization of a Rydberg electromagnetically induced transparency (EIT) system operating in the quantum regime, where optical readout noise is reduced below the shot noise limit using a squeezed vacuum probe field. The experiment employs squeezed light off-resonance with the cesium D2 transition, generated via parametric down-conversion, and transmits it through a thermal atomic vapor cell.
The important innovation of the study lies in the utilization of Doppler - tuned velocity - selective excitation in conjunction with a squeezed probe light and coherent coupling light. This method selectively targets atomic velocity groups that meet the two - photon resonance condition, effectively curbing absorption losses while preserving Electromagnetically Induced Transparency (EIT) coherence. As a result, the atomic medium acts as a tunable, low-loss optical interface, enabling the coherent propagation of squeezed light.
Noise spectral measurements indicate that absorption-induced noise serves as the predominant mechanism accountable for squeezing degradation, whereas excess atomic noise merely plays a secondary role. Under optimized Electromagnetically Induced Transparency (EIT) conditions, the transmitted probe field retains a substantial proportion of the input noise squeezing, which shows that quantum noise reduction can endure passage through a Rydberg atomic ensemble.
Through experimental validation of the preservation of nonclassical light within a Rydberg Electromagnetically Induced Transparency (EIT) medium, this study establishes a novel intersection among quantum optics, atomic physics, and precision metrology. The findings offer a crucial experimental basis for quantum - enhanced atomic sensors and open up prospects for applications like high - sensitivity microwave electric - field detection with the use of Rydberg atoms.
