Decoherence Dynamics of Hole Spin Qubits in Self-Assembled Quantum Dots

Self-assembled InGaAs quantum dots are amongst the most performant solid-state quantum emitters. At the same time, they can host electron or hole spin qubits which can be manipulated using ultrafast laser fields. The electron spin coherence time has been previously shown to be limited by strong contact hyperfine coupling to the noisy nuclear spin environment. A straightforward approach to mitigate the influence of nuclear spin noise involves encoding the qubit on the spin of a valence band hole which, compared to the electron, has much weaker, albeit anisotropic hyperfine coupling. Here, we probe the inhomogeneous dephasing time of a single hole spin qubit (T₂^*) using all optical ultrafast pump-probe techniques and obtain T₂^*&gt;200ns at zero B-field, a value two orders of magnitude longer than for electrons. Ramsey interference measurements performed for various transverse magnetic fields reveal hole spin coherence times in the nanosecond regime and a characteristic nonlinear decrease of the hole spin coherence time with increasing magnetic field. This observation is attributed to the influence of the electrical noise on the spin via the electric field dependent hole g-factor.<br/>To determine the decoherence dynamics and its underlying physical processes, we perform spin echo measurements of the single hole spin which reveal a strong spin echo envelope modulation with two discrete frequencies. A fast oscillation of the spin echo signal (4.8MHz/T) is identified as being due to the effect of quadrupolar coupling on the longitudinal nuclear field component. Uniquely to the hole spin, we observe an additional slow oscillation (0.8MHz/T) that is identified as stemming from a bimodal g-factor behavior, potentially induced by the high intensity rotation laser pulse changing the local electric environment in the vicinity of the quantum dot.