An on-chip superconducting clock with two modes

A superconducting clock based on a 2-junction SQUID (superconducting quantum interference device) flip-flop with feedback is presented. The feedback consists of transmission lines that emanate from and return to the SQUID; the entire clock is built as a compact integrated circuit. The period of the clock is mainly determined by the length of transmission line, and there are two modes of operation that can be separately excited whose periods are in a ratio of 2:1. I-V data for a pair of clocks with different designed periods confirm the presence of the two modes, show how period depends on length, and give information on the switching time of the SQUID flip-flops. Specifically, the I-V data show that there exist both a fundamental model for flux bias at odd multiples of Φ ₀/2 (half-flux quantum) and a doubled mode with precisely half the period flux bias at even multiples. Clocks with longer transmission lines have longer periods, but simple scaling does not occur due to other sources of time delay