Minimum-width control-current pulse for Josephson logic gates

For a given level of overdrive, there exists a minimum-width control-current pulse that must be applied to switch a Josephson logic gate. Determination of this minimum pulsewidth is useful in setting limits on the speed of various Josephson circuit configurations and also in finding the narrowest pulse that a Josephson-junction gate can detect when it is employed as a pulse detector. The minimum control-current pulsewidth is a strong function of the overdrive factor of the control current. It scales as (C/I_{m})^{1/2} , where I m is the junction critical current, and C is the capacitance, and is on the order of 10 ps for Josephson quantum interferometers in 5-µm technology. Computer simulations have been done to find the dependence of minimum control-current pulsewidths on overdrive magnitude for a single-junction gate and for two- and three-junction interferometers. Analytic expressions of the minimum control-current pulsewidth that are in good agreement with simulations have been obtained for these three types of Josephson logic gates.