Rapid single flux quantum

In electronics, rapid single flux quantum (RSFQ) is a digital electronics technology that uses superconducting devices, namely Josephson junctions, to process digital signals. In RSFQ logic, information is stored in the form of magnetic flux quanta and transferred in the form of Single Flux Quantum (SFQ) voltage pulses. RSFQ is one family of superconducting or SFQ logic. Others include Reciprocal Quantum Logic (RQL), ERSFQ - energy-efficient RSFQ version that does not use bias resistors, etc. Josephson junctions are the active elements for RSFQ electronics, just as transistors are the active elements for semiconductor electronics. RSFQ is a classical digital, not quantum computing, technology.

RSFQ is very different from the CMOS transistor technology used in conventional computers:

An SFQ pulse is produced when magnetic flux through a superconducting loop containing a Josephson junction changes by one flux quantum, Φ0 as a result of the junction switching. SFQ pulses have a quantized area ʃV(t)dt = Φ0 ≈ 2.07•10-15 Wb = 2.07 mV ps = 2.07 mA pH due to magnetic flux quantization, a fundamental property of superconductors. Depending on the parameters of the Josephson junctions, the pulses can be as narrow as 1 ps with an amplitude of about 2 mV, or broader (e.g., 5–10 ps) with correspondingly lower amplitude. The typical value of the pulse amplitude is approximately 2IcRn, where IcRn is the product of the junction critical current, Ic, and the junction damping resistor, Rn. For Nb-based junction technology IcRn is on the order of 1 mV.

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References

  1. Yerosheva, Lilia Vitalyevna; Peter M. Kogge (April 2001). "High-Level Prototyping for the HTMT Petaflop Machine (2001)". Department of Computer Science and EngineeringNotre Dame, Indiana.
  2. Bunyk, Paul, Mikhail Dorojevets, K. Likharev, and Dmitry Zinoviev. "RSFQ subsystem for HTMT petaFLOPS computing." Stony Brook HTMT Technical Report 3 (1997).

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