Superconducting electronics
Context and objectives
Research activities on superconducting electronics are mostly based on Rapid Single-Flux-Quantum (RSFQ) digital Electronics. Associated digital circuits use the Josephson tunnel junction as the basic component that is, for superconducting electronics, the device equivalent to transistors in the semiconductor world.
RSFQ circuits use Josephson junctions that are resistively shunted in a careful way in order to be able to generate, propagate and store the binary information through quanta of magnetic flux h/2e (h is Planck's constant and e is the elementary charge) corresponding to 2,0710-15 Wb. This binary information propagates through the circuit as quantized voltage pulses whose area is 2.07 mV.ps. The pulse duration being of the order of a few picoseconds, the repetition rate of such pulses, that is the maximum clock frequency that RSFQ circuits can handle, is of several tens to several hundreds of GHz. Pulse propagation takes place without losses in the superconducting circuits at a speed close to half the light speed. The presence of a quantized pulse in a given time interval is digitally coded as '1', while the absence of such pulse is coded as '0'. Binary information is stored in the circuits as a permanent current running in a superconducting loop. The flux associated to this current corresponds to the magnetic flux quantum: it equals L I = 2,07 pH.mA, where L is the inductance of the storing loop.
Superconducting electronics is of great interest for several niche applications, like ultrafast routers for communication networks, analog-to-digital converters working in the microwave field, and ultra sensitive digital receivers, which have no counterpart in the semiconductor world.
Expertise
Activities in the RSFQ field have started in 1997 on the Savoie-located part of the laboratory; this provides us an expertise unique in France. We have established a software environment for RSFQ design, along with measurements benches that allow us to perform routine laboratory tests of RSFQ circuits. We have also tested RSFQ circuits in a specific low-noise underground environment in the frame of the digital SQUID activities. The RSFQ circuits that are being studied are so far fabricated by the FLUXONICS foundry in the frame of a European collaboration.
DigitalSQUID Magnetometer
Design of RSFQ Analog-to-Digital Converters (ADCs)
Date of update November 26, 2019