QDev Seminar: Tim Botzem

Institute for Quantum Information, RWTH-Aachen University

High fidelity control and coherence of two-electron spin qubits in GaAs quantum dots

I will present our method to experimentally realize high-fidelity single qubit operations for a qubit encoded in two electron spins in GaAs quantum dots by iterative tuning of the all-electrical control pulses. We find an average gate fidelity of F = 98.5% and determine gate leakage out of the computational subspace to L = 0.4%. These results demonstrate that high fidelity gates can be implemented even in the presence of nuclear spins.
Furthermore, I will show that quadrupolar broadening of the nuclear Larmor precession reduces electron spin coherence via faster decorrelation of transverse nuclear fields. However, this effect disappears for appropriate field directions. Furthermore, we observe an additional modulation of coherence attributed to an anisotropic electronic g-tensor. These results complete our understanding of dephasing in gated quantum dots and point to mitigation strategies.