Extended Data Fig. 10: Theoretical effect of tunnel broadening on the charge-stability diagrams.

In some charge-stability diagrams in which level repulsion is weak, such as Fig. 2a and Extended Data Fig. 4, some residual conductance is visible even when μ_LD = μ_RD = 0. This creates the visual feature of the two conductance curves appearing to ‘touch’ each other at the centre. In the main text, we argued that this is owing to level broadening. Here we plot the numerically simulated charge-stability diagrams at zero temperature under various dot-lead tunnel coupling strengths. We use coupling strengths t = 20 μV and Δ = 10 μV as an example. From panels a–c, increasing the tunnel coupling and thereby level broadening reproduces this observed feature. When the level broadening is comparable with the excitation energy, |t − Δ|, finite conductance can take place at zero bias. This feature is absent in, for example, Fig. 2c, in which |t − Δ| is greater than the level broadening.