Non-local modulation of supercurrent in a quantum-dot Josephson junction coupled to a secondary quantum dot

Quantum dot-superconductor arrays represent a promising platform for the realization of Kitaev chains [1,2]. Recently, a two-site Kitaev chain hosting poor man’s Majorana bound states has been demonstrated using two quantum dots coupled via a superconductor [3,4]. However, to achieve a robust topological phase it is necessary to increase the number of sites, thereby introducing multiple coupled quantum-dot Josephson junctions with non-trivial current-phase relations. In a quantum-dot Josephson junction, the phase of the ground state switches between 0 and π depending on the parity of the quantum dot [5]. However, its phase diagram is expected to be modified when coupled to another quantum dot [6]. Here, we use a hybrid InSb/Al nanowire to form a quantum-dot Josephson junction coupled to an additional quantum dot via elastic co-tunnelling and crossed Andreev reflection. We observe that the secondary dot has a strong non-local effect on the supercurrent, indicating a deviation from the usual 0-π transition.

[1] A. Y. Kitaev, Phys.-Usp. 44, 131 (2001).

[2] J. D. Sau and S. D. Sarma, Nat Commun 3, 964 (2012).

[3] M. Leijnse and K. Flensberg, Phys. Rev. B 86, 134528 (2012).

[4] T. Dvir et al., Nature 614, 445 (2023).

[5] J. A. van Dam et al., Nature 442, 667 (2006).

[6] M. Kocsis et al., arXiv:2303.14842 (2023).