Fig. 1: The phase-slip qubit.
a Circuit schematic of the device. The superinductance (green) is in parallel with a superconducting constriction (pink) where flux quanta can tunnel into and out of the loop at a rate Es, i. The arrows indicate the strength and chirality of the current in the loop for fluxon states, m = −1, 0, 1, when the external flux, Φext, is slightly off of zero flux. b False-colored SEM image of lithographically similar device to Device A with the superinductance shown in green and the constriction shown in pink. The qubit is inductively coupled to a readout resonator (light gray). Scale bar corresponds to 5 μm. c Atomic force microscopy image of the 18 nm wide constriction forming the QPS junction. Scale bar corresponds to 100 nm. d Transition energy spectrum from the ground state of a phase-slip qubit as a function of Φext. At zero flux, the qubit frequency is mainly determined by EL, provided that EL ≫ Es,i. The insets show the wavefunctions of the ground (navy), first (blue), and second-excited (orange) states at Φext = 0, 0.25 and 0.5 Φ0.
