NIST’s Single Flux Quantum Waveform Synthesizer
To generate quantum-accurate signals at the super-high frequencies needed for next-gen wireless communication, NIST is developing an ultra-fast waveform generator. It works by transferring discrete, exactly quantized units of magnetic flux (“single flux quantum,” or SFQ) along a circuit made of a series of Josephson junctions, each of which consists of two tiny superconducting electrodes separated by a very thin barrier. A SFQ is stored as a persistent current in the superconducting loop formed by adjacent junctions. Applying a current pulse in addition to the current already passing through a junction can cause the junction to switch and the SFQ to be transferred to the next junction in the series. At the end of the line, the SFQ transfer creates a voltage pulse waveform, emitted at frequencies 10 to 100 times higher than those used in today’s cell phones.
September 25, 2018