# Coherently driving a single quantum two-level system with dichromatic laser pulses

## TL;DR

This paper introduces a novel background-free two-color laser excitation method for single quantum systems, enabling high-purity, indistinguishable single-photon generation without spectral overlap, demonstrated experimentally with quantum dots.

## Contribution

The study presents a phase-locked dichromatic excitation technique that avoids spectral overlap with the transition, improving single-photon source purity and indistinguishability.

## Key findings

- Single photons with purity 0.988(1) and indistinguishability 0.962(6) were generated.
- The method allows phase-coherent control of a two-level system.
- Experimental demonstration with a quantum dot embedded in a micropillar.

## Abstract

Efficient excitation of a single two-level system usually requires that the driving field is at the same frequency as the atomic transition. However, the scattered laser light in solid-state implementations can dominate over the single photons, imposing an outstanding challenge to perfect single-photon sources. Here, we propose a background-free method using a phase-locked dichromatic electromagnetic field with no spectral overlap with the optical transition for a coherent control of a two-level system, and we demonstrate this method experimentally with a single quantum dot embedded in a micropillar. Single photons generated by pi excitation show a purity of 0.988(1) and indistinguishability of 0.962(6). Further, the phase-coherent nature of the two-color excitation is captured by the resonance-fluorescence intensity dependence on the relative phase between the two pulses. Our two-color excitation method adds a useful toolbox to the study of atom-photon interaction, and the generation of spectrally isolated indistinguishable single photons.

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Source: https://tomesphere.com/paper/1905.00275