Synchronous switching of a large number of Josephson junctions

A circuit that allows at least 400 junctions connected in series to be synchronously switched is described. Instead of a few millivolts for a single junction, an array of 400 junctions switches directly to one volt. The junctions, integrated into a stripline circuit similar to that described for series array voltage standards, are commonly biased by a DC current source. When the DC bias is increased the junction with the smallest critical current first switches to the normal state. This causes a pulse to propagate along the stripline, forcing the rest of the junctions to be switched to the normal state. The maximum number of junctions to be switched is proportional to the average critical current of the circuit. The switching time is mainly determined by the signal speed of the pulse in the stripline. Relatively large junctions were used in this experiment. As a result, the length of the stripline containing, for instance, 400 junctions is 16.8 mm. If the junction with the smallest critical current is located in the center of the stripline the switching pulse takes 70 ps to completely pass the line. This time interval can certainly be reduced by a factor of five when smaller junctions are used