Demonstrated Readout of a QFP Logic Element with an RQL Josephson Transmission Line

Recent interest in superconducting digital logic has increased as demonstrated by the IARPA Cryogenic Computing Complexity (C3) program with AQFP logic and RQL logic demonstrated as leading competitors with complex logic and large-scale device demonstrations [1, 2]. In a fully realized cryogenic digital computer, it may be beneficial to utilize both logic families for optimal performance. To that end, we demonstrate the first generalizable, reliable mapping of Quantum Flux Parametron (QFP) circulating states into Reciprocal Quantum Logic (RQL) single flux quantum pulse pairs. By simultaneously measuring the QFP state with both a flux tunable resonator and RQL, we verify that the RQL components of our circuit are faithfully transmitting the digital information stored in the QFP state. The individual bit error rate of this process does not exceed 2E-6 at a maximum reference clock frequency of 6 GHz, and is limited only by the length of the measurement.

1. A. Y. Herr et al, “An 8-bit carry look-ahead adder with 150 ps latency and sub-microwatt power dissipation at 10 GHz,” J. Appl. Phys. 13, 033911 (2013).

2. K. Inoue et al., “Simulation and Implementation of an 8-bit Carry Look-Ahead Adder Using Adiabatic Quantum-Flux-Parametron”, ISEC, 2013 IEEE 14th International (2013).