Tuning singlet vs triplet Cooper-pair splitting in InSb nanowires*

Cooper pairs are a natural source of entangled electrons provided by superconductors. Semiconducting-superconducting hybrid systems allow the splitting of Cooper pairs into separate single electrons and their subsequent manipulation. Using two few-electron InSb nanowire quantum dots separated by a narrow strip of proximitized superconducting Al, we achieve a high degree of control in Cooper-pair splitting via selecting for the single electron's desired charge as well as spin. The resulting Cooper-pair splitting signal is free of contributions from the competing process, elastic co-tunneling. Under an applied magnetic field parallel to the Rashba spin-orbit field of InSb, we observe complete blockade of the equal-spin splitting process due to spin-singlet superconducting pairing. Rotating the applied field to be perpendicular to the Rashba field introduces a triplet component in the effective superconducting pairing between electrons and lifts this blockade. The spin blockade results open new pathways to the precise manipulation and entanglement testing of the split electrons.