Superconducting spin qubits: coherence, coupling and perspective*

Andreev spin qubits (ASQs) have recently emerged as an alternative qubit platform with realizations in semiconductor-superconductor hybrid nanowire Josephson junctions [1,2]. In these qubits, the spin degree of freedom is intrinsically coupled to the supercurrent across the junction, which facilitates fast, high-fidelity spin readout and strong spin-spin coupling. In this talk, I will discuss our results on the implementation of an Andreev spin qubit that is stabilized by the charging energy of a gate-defined quantum dot [2, 4, 5]. The qubit state can be directly manipulated via electric dipole spin resonance and its frequency can be tuned with a magnetic field. Additionally, 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 [6]. The qubit-qubit interaction is both gate- and flux-tunable and it can be switched off on demand using a magnetic flux. Finally, I will discuss the prospect of using Andreev spin qubits as a platform for quantum computing and simulation.

[1] M. Hays et al., Science 373, 6553 (2021). 

[2] Pita-Vidal, Bargerbos et al., Nature Physics, 10.1038/s41567-023-02071-x (2023).  

[3] Padurariu and Nazarov, Phys. Rev., B 81, 144519 (2010). 

[4] Bargerbos, Pita-Vidal et al., PRX Quantum, 3, 030311 (2022). 

[5] Bargerbos, Pita-Vidal et al., Phys. Rev. Lett. 131, 097001 (2023). 

[6] Pita-Vidal, Wesdorp et al., arXiv:2307.15654 (2023).