Demonstration of spatial-light-modulation-based four-wave mixing in cold atoms

TL;DR

This paper demonstrates a spatial-light-modulation-based four-wave mixing process in cold atoms, achieving a 43% wavelength conversion efficiency, and discusses its potential to reach near-unity efficiency for quantum information applications.

Contribution

The study introduces a novel spatial-light-modulation scheme for FWM in cold atoms, significantly improving conversion efficiency over traditional EIT-based methods.

Findings

Achieved 43% wavelength conversion efficiency in cold $^{87}$Rb atoms.

Theoretical model predicts up to 96% efficiency at higher optical densities.

Scheme enables near-unity efficiency, promising for quantum wavelength conversion.

Abstract

Long-distance quantum optical communications usually require efficient wave-mixing processes to convert the wavelengths of single photons. Many quantum applications based on electromagnetically induced transparency (EIT) have been proposed and demonstrated at the single-photon level, such as quantum memories, all-optical transistors, and cross-phase modulations. However, EIT-based four-wave mixing (FWM) in a resonant double-$\Lambda$ configuration has a maximum conversion efficiency (CE) of 25% because of absorptive loss due to spontaneous emission. An improved scheme using spatially modulated intensities of two control fields has been theoretically proposed to overcome this conversion limit. In this study, we first demonstrate wavelength conversion from 780 to 795 nm with a 43% CE by using this scheme at an optical density (OD) of 19 in cold $^{87}$Rb atoms. According to the theoretical model, the CE in the proposed scheme can further increase to 96% at an OD of 240 under ideal conditions, thereby attaining an identical CE to that of the previous non resonant double-$\Lambda$ scheme at half the OD. This spatial-light-modulation-based FWM scheme can achieve a near-unity CE, thus providing an easy method of implementing an efficient quantum wavelength converter for all-optical quantum information processing.