Qdev seminar by Marta Pita Vidal, Delft University of Technology

Title: Andreev spin qubits

Andreev spin qubits (ASQs) have recently emerged as an alternative qubit platform with realizations in semiconductor-superconductor hybrid nanowire Josephson junctions. In these qubits, the spin degree of freedom is intrinsically coupled to the supercurrent across the junction via the spin-orbit interaction, which facilitates fast, high-fidelity spin readout using circuit quantum electrodynamics techniques. Moreover, this spin-supercurrent coupling has been predicted to facilitate inductive multi-qubit coupling via a shared inductance. Here, I will discuss our recent results on the implementation of an Andreev spin qubit which is stabilized exploiting the charging energy of a gate-defined quantum dot. In this device, the qubit state can be directly manipulated via electric dipole spin resonance and its frequency can be tuned over more than 12 GHz using a magnetic field. We will also see how the ASQ can be coherently coupled to a transmon qubit. I will furthermore discuss measurements of strong supercurrent-mediated longitudinal coupling between two distant Andreev spin qubits. Finally, I will show that this qubit-qubit interaction is both gate- and flux-tunable up to a coupling strength of 179 MHz and that it can be switched off on demand using a magnetic flux. These results demonstrate that integrating microscopic spin states into a superconducting qubit architecture can combine the advantages of both semiconductors and superconducting circuits and pave the way to fast, high-fidelity two-qubit gates between remote spins.