In electronics, rapid single flux quantum (RSFQ) is a digital electronic device 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.
Others include Reciprocal Quantum Logic (RQL), ERSFQ – energy-efficient RSFQ version that does not use bias resistors, etc.
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.