Three-dimensional sketch of a superconducting amplifier: the current Ia flowing in the bottom thin film (in black) modulates the critical current of the built-on vertical Josephson interferometer.
Circuit diagrams for: (a) a two-junction interferometer and (b) a four-terminal device consisting of a double junction interferometer having a current Ia flowing in its lower arm, which necessitates partitioning the inductances. The junctions are marked by an ×.
Numerically computed positive and negative interferometer threshold curves ic (ϕe ) with = Icr and + βr = 2: (a) symmetric case, = βr = 1, and (b) (fully) asymmetric case = 0 and βr = 2. In the experiments, only the stable solutions are measured, which correspond to the upper and lower envelopes of the threshold curves.
Sketch (not in scale) of two linear current amplifiers based on vertical Josephson interferometers. The base electrode is in black, the top electrode is in gray, and the junction area is white: (a) symmetric bias and (b) asymmetric bias.
(a) A vertical double-junction interferometer (in gray) can count the number of flux quanta trapped in a superconducting loop (in black); (b) its equivalent circuit. and are two independent control variables.
Sketch (not in scale) of two circular vertical double junction interferometers. The base electrode is in black, the top electrode in gray, and the junction area is white: (a) symmetric bias and (b) asymmetric bias.
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