Topological superconductors are promising building blocks for future quantum computers, although their experimental  realization  remains  a  challenging  task. In this talk, I will present theory results on a Josephson junction with a double quantum dot, a minimal model system toward engineered topological superconductivity based on quantum dot chains [1].  In  the  (1,1) charge  sector of the serially coupled double quantum dot, I will illustrate a magnetically  induced  singlet-triplet  ground-state  transition  via  triplet blockade: the Josephson current carried by the triplet ground state at high magnetic field is much suppressed compared to the current carried by the singlet ground state at low magnetic field. The theory results I present are based on the zero-bandwidth approximation. I will provide simple arguments for a strong triplet blockade in the large-gap, and the strong-Coulomb-repulsion limit. Furthermore I also outline  a  process-counting argument that supports partial triplet blockade in the intermediate  regime, using perturbation theory. I will also present experimental data showing the triplet blockade predicted by the theory. The triplet blockade mechanism could provide a coupling mechanism between spin qubits, and (topological or non-topological) superconducting qubits.

 

[1] Bouman et al, arXiv:2008.04375