Rabi oscillations of a quantum dot exciton coupled to acoustic phonons: coherence and population readout

TL;DR

This paper investigates Rabi oscillations of a single quantum dot exciton driven by ultrafast optical pulses, revealing the effects of phonon coupling on coherence and population dynamics through combined experimental and theoretical analysis.

Contribution

It demonstrates the direct observation of Rabi oscillations in a quantum dot exciton using four-wave mixing spectroscopy and analyzes phonon effects on these dynamics.

Findings

Rabi oscillations observed via four-wave mixing spectra.

Coupling to acoustic phonons affects exciton coherence.

Autler-Townes splitting confirms dressed state formation.

Abstract

While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optically driven dynamics of a single exciton quantum state confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain this oscillation generates the Autler-Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the FWM dynamics on the picosecond timescale, because it leads to transitions between the dressed states.