Quantum theory of the dc Josephson effect: Static tunneling characteristics of ultrasmall Josephson junctions

Abstract

We examine the static tunneling characteristics of ultrasmall Josephson junctions that are current biased on the zero-voltage dc step. Novel scaling, magnetic, and thermal characteristics are exhibited by the supercurrent as the device is scaled down from the 1.0 to the 0.01 μ${\mathrm{m}}^2$ regime. Furthermore, the noise voltage is found to peak for devices in which the electrostatic energy required to transfer a pair is equal to the interaction energy between the two superconductors. For such junctions, noise voltages are on the order of several mV, and the magnitude of the supercurrent is found to be a very sensitive function of device area and operating temperature. Finally, these features of the junction's dynamics have technological implications regarding digital applications of such devices.