A POSSIBLE QUANTUM CURRENT STANDARD BASED ON A SUPERCONDUCTING WEAK-LINK

William H. Howard, Y. H. Kao

A. Baratoff, James A. Blackburn, Brian B. Schwartz

CHENG GENG-HUA, ZHANG YU-HENG, (1)中国科学技术大学物理系,合肥; (2)中国科学技术大学物理系,研究生

It is pointed out that if a superconducting ring containing a weak link is placed in a cavity, which is in resonant with the current flowing in the ring, i.e., when the frequency of the Josephson current or one of its n-th harmonies is equal to the cavity frequency, and if the cavity has sufficiently high Q-value, then the feedback of the stationary electric-magnetic wave will act on the ring itself and produce a small sinusoidal oscillation superposing on the primary sawtooth wave oscillating current. The period of the small oscillation will be φ0/n and its amplitude that of the sawtooth wave multiplied by 1/nπ.

J.C. Gallop, W.J. Radcliffe

Connor D. Shelly, Patrick See, Ivan Rungger +1 more

We present measurements of microwave-induced Shapiro steps in a superconducting nanobridge weak link in the dissipative branch of a hysteretic current-voltage characteristic. We demonstrate that Shapiro steps can be used to infer a reduced critical current and an associated local temperature. Our observation of Shapiro steps in the dissipative branch shows that a finite Josephson coupling exists in the dissipative state. Although the nanobridge is heated, our model shows that the temperature remains below the critical temperature. This work provides evidence that Josephson behavior can still exist in thermally hysteretic weak-link devices and will allow extension of the temperature range over which nanobridge-based single-flux-quantum circuits, micron-sized superconducting quantum interference devices (i.e., nanoSQUIDs), and Josephson voltage standards can be used.