Spin qubits in SiGeUrheberrecht: © T. Leonhardt
We test different encodings to represent a qubit by electron spins for scalable quantum computation in SiGe. The simplest encoding is to use the spin-up and spin-down state of a single electron spin in a magnetic field as the qubit 0 and 1 states. This approach is taken in the famous proposal by Loss and DiVincenzo and also pursued in GaAs . Single qubit operations are performed by electron spin resonance. Since local AC magnetic fields are hard to achieve locally , we exploit spin manipulation by AC electric fields in an inhomogeneous magnetic field generated by a micro-magnet (marked in red in the figure) .
We improve the quality of the electrostatically defined quantum dots by replacing the dopant layer by electron inducing top gates and aiming at smaller electrostatic gate patterns (in cooperation with FZ Jülich and IHT RWTH Aachen).
We investigate the electrical and magnetic sources of spin decoherence in silicon. Therefore we analyze the role of charge-noise on qubit gate fidelities. Furthermore we compare the qubit decoherence in samples with a natural abundance of silicon isotopes (29Si exhibits a nuclear spin) and isotopically purified samples.
A list of relevant group publications is given below (see External Links).
-  Single-Shot Correlations and Two-Qubit Gate of Solid-State Spins, Nowack et al., Science (2011)
-  Excitation of a Si/SiGe quantum dot using an on-chip microwave antenna, Kawakami et al., App. Phys. Lett. (2013)
-  Simulation of micro-magnet stray-field dynamics for spin qubit manipulation, Neumann and Schreiber, J. Appl. Phys.(2015)