Quantifying quantum coherence of multiple-charge states in tunable Josephson junctions

LZSM interferometry

Before presenting the experimental results, we first interpret the physical picture of LZSM interference in an ultra-small JJ. Phase fluctuations lead to the loss of macroscopic quantum coherence and Cooper pair tunneling as individual microscopic particles^9,12,13 (Fig. 1a). MARs enable a coherent transfer of 2-charges through a 1st-order reflection (Fig. 1b) and 3-charges through a 2nd-order reflection (Fig. 1c). Single charge tunneling is activated when the voltage reaches V_b = 2Δ/e (Δ is the superconducting gap and e is the elementary charge) (Fig. 1d)….