Extended Data Fig. 4: Conductance spectra of two-site QD pairs.

Studying CSDs for pairs of QDs provides information about the interdot couplings and allows one to reach the sweet spot conditions shown in Fig. 1c,d. In addition, finite bias conductance spectra at the two-site sweet spots should be obtained³⁵ for all possible combinations of QD detunings. This is shown here for the charge configuration in Fig. 1. Adjacent schematics represent the configurations of the QDs and the parameters varied. Left column: tunneling spectroscopies of the left QD pair at a sweet spot (i.e. t₁ = Δ₁), with the right QD kept in Coulomb blockade. G_LL and G_MM are measured as a function of a. detuning V_QDL, b. detuning V_QDM, c. detuning both V_QDL and V_QDM simultaneously and d. Applying a magnetic field B_z perpendicular to the superconducting loop. Right column: tunneling spectroscopy of the right pair of QDs at a sweet spot (i.e. t₂ = Δ₂), with the left QD kept in Coulomb blockade. G_MM and G_RR are measured as a function of e. detuning V_QDRf. detuning V_QDM, g. detuning both V_QDM and V_QDR and h. Applying a magnetic field B_z perpendicular to the superconducting loop. It is important to note that (d) and (h) are obtained for the same configuration as the flux-dependence measurements in Fig. 2, with the only difference being that here the outer QD is kept in Coulomb blockade. The lack of response to B_z rules out more trivial origins of the flux dependence in Fig. 2, such as oscillations of the middle QDs electrochemical potential energy.