Spin Qubits in GaAsCopyright: © Gate adjustment by iterative tomography. From arXiv:1606.01897
We study the fundamental device-physics of spin qubits in GaAs/(Al,Ga)As as well as we pursue their technological development for multi-qubits operations. One focus of current activities is high-fidelity qubit manipulation based on numerically optimized control pulses and in-situ tuning (see figure). Simulations indicate that gate fidelities compatible with quantum error corrections should be achievable [1,2], as also confirmed by recent experimental results . Furthermore, we are developing improved dynamic nuclear polarization techniques to reduce dephasing due to nuclear spins by controlling their polarization using the qubit and exploring the limits of their performance and the properties of the resulting special, so called "narrowed" states.
We have developed new measurement schemes based on correlating the outcomes of subsequent initialize-evolve-measure-cycles that can probe the dynamics of the environment seen by a quibit over a wide range of time scales. Applied to our quibts, they reveal the importance of the Larmor precession of nuclear spins and their dephasing . Another area of interest is the interplay between nuclear spins and spin orbit coupling.
A major topic of future work will be the realization of multi-qubit circuits and the mitigation of charge noise, which is another important factor for qubit performance.
A list of relevant group publications is given below (see External Links).
-  High-Fidelity Single-Qubit Gates for Two-Electron Spin Qubits in GaAs, P. Cerfontaine et al., PRL 113, 150501 (2014)
-  A High-Fidelity Gateset for Exchange-Coupled Singlet-Triplet Qubits, P.Cerfontaine et al., arXiv:1901.00851 (2019)
-  Closed-loop control of a GaAs-based singlet-triplet spin qubit with 99.5% gate fidelity and low leakage, P. Cerfontaine et al., arXiv:1906.06169
-  Quadrupolar and anisotropy effects on dephasing in two-electron spin qubits in GaAs, T. Botzem et al., Nature Communications 7, 11170 (2016)