Wavelength Conversion of Single Photons from a Quantum Dot in Warm Cs Vapor

We report our progress on experimentally demonstrating conversion of single ~894 nm photons produced from a quantum dot to wavelengths suitable for long distance communication via optical fiber (~1469 nm) or via ground-to-satellite link (~794 nm) using warm caesium vapor. The quantum dot (QD) is grown inside a semiconductor nanowire and offers a bright source of single photons and entangled photon pairs. The QD emission is precisely tuned to near the Cs D₁ line at ~894.6 nm by our recently developed gas deposition technique, in which nitrogen gas deposited on the nanowire surface shifts the QD emission wavelength. The conversion is realized via a four-wave-mixing process in vapor, where two classical pump fields interact with the input photons to convert them to the target wavelength. To achieve maximum conversion efficiency, we obtain parameters for the two pump fields, as well as for the detuning of the quantum dot photon, from our numerically optimized model that accounts for the hyperfine structure and Doppler broadening of the atoms.