Fig. 1. (a) Three states of nanowire: (i) superconducting state, (ii) hotspot state, (iii) normal state (“latched” state). ψ_1,2 denotes the wave function at both ends of the nanowire. (b) Schematic diagram of simplified nanowire model. L₁ denotes the inductance of nanowire. R_hs represents the resistance of hotspot region in hotspot state. SW refers to the switching effect of nanowires. SW is open for hotspot state, while closed for superconducting state.

Fig. 2. (a) Schematic diagram of two parallel ultrathin superconducting nanowires. I_bias is the current through parallel nanowires, i_1,2 denote the currents in nanowires, and i_flux represents the circulating current due to external magnetic flux Φ_e. The direction of circulation depends on fluxoid number n. (b) Equivalent circuit of parallel nanowires based on switch model. L_1,2 denotes nanowire’s inductance. SW_1,2 represents the switching effect of the nanowire. SW_1,2 is open for hotspot state with hotspot resistance R_hs, while closed for superconducting state. (c) Simulation results of flux-to-voltage conversion curves in parallel nanowires. The bias currents for different curves increase from 1.3 ⋅ I_sw to 2.5 ⋅ I_sw in steps of 0.2 ⋅ I_sw from bottom to top. Modulation disappears due to the latching effect.

Fig. 3. (a) Schematic diagram of the nanowire interference device with a shunt resistor. It comprises two parallel ultrathin superconducting nanowires shunted with resistor R_shunt. External inductance L_shunt is taken into consideration to estimate the effect of parasitic parameters. Φ_e is the external magnetic flux applied to the device. i_1,2,3 denote the currents through the parallel nanowires and the shunt resistor respectively. (b) Equivalent circuit of the device with a shunt resistor. Φ_e is the external magnetic flux applied to the device. L_1,2 denote the inductances of nanowires. SW_1,2 denote the switching effect of nanowires. SW_1,2 is open for hotspot state with hotspot resistance of R_hs, while it is closed for the superconducting state.

Fig. 4. (a) Simulation results of current–voltage characteristic with a shunt resistor. Bias current is normalized by switching current of single nanowire I_sw, and output voltage is normalized by the multiplication of switching current and shunt resistance. (b) Simulation results of flux-to-voltage conversion curves. Bias currents of flux modulation curves increase from 1.1 ⋅ I_sw to 2.5 ⋅ I_sw in steps of 0.2 ⋅ I_sw from bottom to top. Each curve has periodicity and symmetry.

Fig. 5. Flux-to-voltage conversion curves for devices with different values of shunt resistance and nanowire inductance. (a) Curves for different values of shunt resistance. Shunt resistances are selected to be 0.01 ⋅ R_hs, 0.05 ⋅ R_hs, 0.1 ⋅ R_hs, 0.15 ⋅ R_hs, and 0.25 ⋅ R_hs respectively from bottom to top for I_bias = 2 ⋅ I_sw. Output voltage is normalized by the multiplication of switching current and hotspot resistance. For a smaller resistor, device can support higher bias current, but output voltage is lower. When resistance becomes larger, device is easier to latch. (b) Flux-to-voltage conversion curves for different values of nanowire inductance of 16.5, 66, 100, 165, 230 pH, respectively, for I_bias = 2 Φ I_sw. Output voltage is normalized by the multiplication of switching current and shunt resistance. As the inductance of nanowire decreases, modulation curve becomes steeper, while output voltage slightly increases.

Table 1. Simulation parameters for device.