Coherent dynamics of a single Mn-doped quantum dot revealed by four-wave mixing spectroscopy

TL;DR

This study uses four-wave mixing spectroscopy to explore the quantum coherence of a Mn-doped quantum dot, revealing how the magnetic ion's spin influences spectral properties and coherence dynamics, advancing understanding of quantum dot spin interactions.

Contribution

It demonstrates the coherent optical response of a Mn-doped quantum dot and uncovers the effects of Mn spin fluctuations on spectral wandering and dephasing.

Findings

Observation of strong photon echo indicating inhomogeneous broadening

Detection of six spectral lines due to Mn spin states

Identification of spectral wandering caused by Mn spin flips

Abstract

For future quantum technologies the combination of a long quantum state lifetime and an efficient interface with external optical excitation are required. In solids, the former is for example achieved by individual spins, while the latter is found in semiconducting artificial atoms combined with modern photonic structures. One possible combination of the two aspects is reached by doping a single quantum dot, providing a strong excitonic dipole, with a magnetic ion, that incorporates a characteristic spin texture. Here, we perform four-wave mixing spectroscopy to study the system's quantum coherence properties. We characterize the optical properties of the undoped CdTe quantum dot and find a strong photon echo formation which demonstrates a significant inhomogeneous spectral broadening. Incorporating the Mn$^{2+}$ ion introduces its spin-5/2 texture to the optical spectra via the exchange interaction, manifesting as six individual spectral lines in the coherent response. The random flips of the Mn-spin result in a special type of spectral wandering between the six transition energies, which is fundamentally different from the quasi-continuous spectral wandering that results in the Gaussian inhomogeneous broadening. Here, the discrete spin-ensemble manifests in additional dephasing and oscillation dynamics.