Quantum interference josephson logic devices

Abstract

A quantum interference Josephson junction logic device is disclosed which comprises three or more junctions connected in parallel which are capable of carrying Josephson current and includes means integral with at least one of the junctions for carrying a larger maximum Josephson current than the remaining junctions. This integral means includes means for carrying a maximum Josephson current which is twice as large as the maximum Josephson current in the remaining junctions. While the spacing between the lobes of the threshold curve (I.sub.m vs. I.sub.c) is increased over that of a two junction interferometer by adding another junction resulting in an increased operating region in which logic circuits switch to the voltage state, good current gains with large lobe separation could not be achieved by the mere addition of junctions. Current gain with large lobe separation is obtained if the two outer junctions having a zero field threshold current, I.sub.o, are connected via an inductance, L, to the center junction with a maximum Josephson current, 2I.sub.o. The gain is maximized if the gate current, I.sub.g, is fed into the device through inductances, L.sub.p, having a value of inductance approximately equal to 3L in the center of inductances L which are disposed between pairs of junctions forming a symmetrical dual feed. Increased gain and operating range can be achieved using the symmetrical dual feed and interferometer arrangements where the maximum Josephson current in all the junctions thereof is the same.