Supercurrent parity meter in a nanowire Cooper pair transistor
Ji Yin Wang (TU Delft - QRD/Kouwenhoven Lab)
Constantin Schrade (Massachusetts Institute of Technology)
Vukan Levajac (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - QRD/Kouwenhoven Lab)
David van Driel (TU Delft - QuTech Advanced Research Centre, TU Delft - QRD/Kouwenhoven Lab, Kavli institute of nanoscience Delft)
Kongyi Li (Kavli institute of nanoscience Delft, TU Delft - BUS/Quantum Delft, TU Delft - QuTech Advanced Research Centre)
Ghada Badawy (Eindhoven University of Technology)
Joon Sue Lee (University of California)
Leo P. Kouwenhoven (TU Delft - Applied Sciences, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, Microsoft Quantum Lab Delft)
Jie Shen (Chinese Academy of Sciences)
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Abstract
We study a Cooper pair transistor realized by two Josephson weak links that enclose a superconducting island in an InSb-Al hybrid nanowire. When the nanowire is subject to a magnetic field, isolated subgap levels arise in the superconducting island and, because of the Coulomb blockade, mediate a supercurrent by coherent cotunneling of Cooper pairs. We show that the supercurrent resulting from such cotunneling events exhibits, for low to moderate magnetic fields, a phase offset that discriminates even and odd charge ground states on the superconducting island. Notably, this phase offset persists when a subgap state approaches zero energy and, based on theoretical considerations, permits parity measurements of subgap states by supercurrent interferometry. Such supercurrent parity measurements could, in a series of experiments, provide an alternative approach for manipulating and protecting quantum information stored in the isolated subgap levels of superconducting islands.
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