Direct measurement of the Josephson plasma resonance frequency from I-V Characteristics

The speed of Josephson circuits such as those required for rapid single flux quantum logic is limited by the Josephson plasma frequency, ω_p, which (with few exceptions) increases monotonically with increasing critical current density, J_c. Here we describe a new technique for directly measuring ω_p, using the current-voltage characteristics of a simple structure based on externally-shunted, series-connected tunnel junctions. We present both experimental and theoretical demonstrations of the technique and describe its application to the determination of the junction capacitance, a property poorly characterized for high-J_c junctions.