Charge carrier dynamics in a solid-state quantum emitter: Auger, dephasing and stochastic resonance

Self-assembled quantum dots (QDs) are semiconductor nanostructures with discrete, atom-like energy levels arising from strong three-dimensional carrier confinement, making them outstanding candidates for solid-state quantum optics. The QD can host a two level system with the possibility of a superposition of states which can be used as a qubit. Furthermore the QD can even act as a spin photon interface, where the spin state can be transmitted via a photon. The ability to do so is governed by the details of their confinement potential and interaction with the environment and therefore can be tailored for different needs in the growth process and be optimized to reduce noise in the system. In this thesis, I investigate the dynamics of single QDs through resonance fluorescence experiments, focusing on how post-growth treatment, magnetic fields, and external driving shape their behavior. In the first part, Auger and spin dynamics in a self-assembled quantum dot, the magneticfield dependence of the Meitner–Auger effect and its impact on spin dynamics is investigated. Using time-resolved n-shot measurements of the trion transition in a weakly tunnel-coupled QD, I quantify the Auger recombination, spin-flip, and spin-flip Raman rates as a function of magnetic field up to 10 T. At B = 0 T, the Auger rate is about 3 1/ms, decreasing to about 1 1/ms at B = 10 T, suggesting that the magnetic confinement alters the overlap of initial and final states of the Auger process. The Auger process randomizes the electron spin, making it a significant decoherence channel in spin–photon interfaces. Our analysis shows that the confinement potential and the density of final states above the QD both contribute to the electron emission rate, and that the spin-flip dynamics are enhanced by magnetic field via Zeeman splitting, with the spin-flip rate increasing while the spin-flip Raman rate remains constant. In the second part, Near transform-limited single photons from rapid-thermal annealed quantum dots, QDs subjected to rapid thermal annealing (RTA) are studied, which tunes their emission energy by promoting Ga–In interdiffusion and modifying the confinement potential. Using resonance fluorescence on single QDs embedded in a p–i–n diode at 4.2 K, we measure an exciton linewidth of about 360 MHz and a radiative lifetime of 670 ps, corresponding to a coherence time T_2 that is only 1.5 times the Fourier limit. Single-photon purity remains excellent, with g(2)(0) ≈ 0.01, confirming the two-level nature of the system and demonstrating that RTA can spectrally tune QDs without compromising their coherence or quantum-optical quality. These results indicate that post-growth thermal treatment is a viable tool for integrating QDs into photonic circuits while maintaining nearly Fourier-limited emission. In the third part, Quantum stochastic resonance in a single-photon emitter, we realize the effect of quantum stochastic resonance in a single QD. By applying a periodic modulation of the gate voltage and monitoring the electron tunneling through photon emission, we observe a resonance in the regularity of tunneling events at a modulation frequency of about 800 Hz. This frequency corresponds well to the rule-of-thumb resonance condition Tmod ∼ 1/ max{γ_in,low, γ_out,high}, where γ_in and γ_out are the rates for electrons tunneling into and out of the QD. We analyze the full counting statistics using factorial cumulants, finding that the resonance frequency shifts systematically with cumulant order. This is a signature of correlations beyond simple Poissonian dynamics. These results demonstrate that this QD–reservoir system enables transport measurements through optical readout and stochastic resonance is visible in this system.