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• It is based on superconductors, so a cryogenic environment is required
• Instead of voltage levels, digital signals are represented by picosecond-duration pulses that travel down superconducting microstrip transmission lines.
• The pulses are single quanta at the lowest energy level allowed by quantum mechanics in the system, and hence cannot change significantly in transit. They do not lose energy, spread out, or interfere.
• The quantum pulses are switched by Josephson junctions instead of transistors
• Unlike normal circuitry, signals cannot be split into multiple outputs without active circuit elements

1 Advantages

• Interoperable with CMOS circuitry
• Extremely fast operating frequency (up to hundreds of gigahertz)
• Low power consumption
• Existing chip manufacturing technology can be adapted to manufacture RSFQ circuitry
• Good tolerance to manufacturing variations
• RSFQ circuitry is essentially self clocking, making asynchronous designs much more practical.

2 Disadvantages

• Requires cryogenic cooling; liquid helium may be necessary unless high-temperature superconductorThe term high-temperature superconductor was initially employed to designate the new family of cuprate-perovskite ceramic materials discovered by J. Bednorz and K. Mueller in 1986. These materials are characterized by presenting superconductivity at a higs can be maufactured in this way.

3 Applications

• Optical and other high-speed network switching devices
• Digital signal processingDigital signal processing DSP is the study of signals in a digital representation and the processing methods of these signals. DSP and analog signal processing are subsets of signal processing. It has three major subfields: audio signal processing, digita, even up to radiofrequency signals.
• High speed analog to digital convertersIn electronics, an analog to digital converter (abbreviated ADC A/D or A to D is a device that converts continuous signals to discrete digital numbers. Typically, an ADC converts a voltage to a digital number. The digital to analog converter or DAC perfor
• Petaflop supercomputers

4 References

• An excellent introduction to the basics and links to further information at the Stony Brook University.
• K.K. Likharev and V.K. Semenov, IEEE Trans. Appl. Supercond. 1 (1991), 3.
• A. H. Worsham, J. X. Przybysz, J. Kang, and D. L. Miller, "A single flux quantum cross-bar switch and demultiplexer," IEEE Trans. on Appl. Supercond., vol. 5, pp. 2996--2999, June 1995.
• Feasibility Study of RSFQ-based Self-Routing Nonblocking Digital Switches (1996)
• Design Issues in Ultra-Fast Ultra-Low-Power Superconductor Batcher-Banyan Switching Fabric Based on RSFQ Logic/Memory Family (1997)
• A Clock Distribution Scheme for Large RSFQ Circuits (1995)
• Josephson Junction Digital Circuits -- Challenges and Opportunities