Nonadiabatic Josephson current pumping by microwave irradiation

Irradiating a Josephson junction with microwaves can operate not only on the amplitude but also on the phase of the Josephson current. This requires breaking time inversion symmetry, which is achieved by introducing a phase lapse between the microwave components acting on the two{\dag} sides of the junction. General symmetry arguments and the solution of a specific single level quantum dot model show that this induces chirality in the Cooper pair dynamics, due to the topology of the Andreev bound state wavefunction. Another essential condition is to break electron-hole symmetry within the junction. A shift of the current-phase relation is obtained, which is controllable in sign and amplitude with the microwave phase and an electrostatic gate, thus producing a "chiral" Josephson transistor. The dot model is solved in the infinite gap limit by Floquet theory and in the general case with Keldysh nonequilibrium Green's functions. The chiral current is nonadiabatic: it is extremal and changes sign close to resonant chiral transitions between the Andreev bound states.Comment: 13 pages, 7 figures, extended versio

Material and integration challenges for large scale Si quantum computing

International audienceSi spin qubits are very promising to enable large scale quantum computing as they are fast, of high quality and small. However, they are still lagging behind in terms of number of qubits. Indeed there are material and integration challenges to be tackled before fully expressing their potential

Towards scalable quantum computing based on silicon spin

International audienc

Challenges and perspectives in the modeling of spin qubits

International audienc