Heralded preparation of spin qubits in droplet-etched GaAs quantum dots using quasiresonant excitation

We present a comprehensive study on heralded spin preparation employing excited state resonances of droplet-etched GaAs quantum dots. This achievement will facilitate future investigations of spin qubit based quantum memories using the GaAs quantum dot material platform. By observation of excitation spectra for a range of fundamental excitonic transitions, the properties of different quantum dot energy levels, i.e., shells, are revealed. The innovative use of polarization-resolved excitation and detection in the context of quasiresonant excitation spectroscopy of quantum dots greatly simplifies the determination of the spin preparation fidelities-irrespective of the relative orientations of laboratory and quantum dot polarization eigenbases. By employing this method, spin preparation fidelities of quantum dot ground states of up to 85% are found. Additionally, the characteristic nonradiative decay time is investigated as a function of ground state, excitation resonance, and excitation power level, yielding decay times as low as 29 ps for s-p shell exited state transitions. Finally, by time-resolved correlation spectroscopy it is demonstrated that the employed excitation scheme has a significant impact on the electronic environment of quantum dot transitions and their apparent brightness.