Atomic Clouds as Spectrally-Selective and Tunable Delay Lines for Single Photons from Quantum Dots

TL;DR

This paper presents a compact, tunable delay line for single photons from quantum dots, using natural atom clouds as slow-light media to achieve controllable delays for photons with very close frequencies.

Contribution

It introduces a novel method combining quantum dot photons and atomic vapors to create spectrally-selective, tunable delay lines with high precision.

Findings

Achieved up to 2.4 ns differential delay for photons 14.5 GHz apart.

Demonstrated spectral selectivity using atomic vapor as a slow-light medium.

Developed a theoretical model explaining the experimental results.

Abstract

We demonstrate a compact, spectrally-selective, and tunable delay line for single photons emitted by quantum dots. This is achieved by fine-tuning the wavelength of the optical transitions of such "artificial atoms" into a spectral window in which a cloud of natural atoms behaves as slow-light medium. By employing the ground-state fine-structure-split exciton confined in an InGaAs/GaAs quantum dot as a source of single photons at different frequencies and the hyperfine-structure-split $D_1$ transition of Cs-vapors as a tunable delay-medium, we achieve a differential delay of up 2.4 ns on a 7.5 cm long path for photons that are only 60 \mu eV (14.5 GHz) apart. To quantitatively explain the experimental data we develop a theoretical model that accounts for both the inhomogeneously broadening of the quantum-dot emission lines and the Doppler-broadening of the atomic lines. The concept we proposed here may be used to implement time-reordering operations aimed at erasing the "which-path" information that deteriorates entangled-photon emission from excitons with finite fine-structure-splitting.