A three-terminal device that exhibits transistor-like functionality at cryogenic temperatures may be formed from a single layer of superconducting material. A main current-carrying channel of the device may be toggled between superconducting and normal conduction states by applying a control signal to a control terminal of the device. Critical- current suppression and device geometry are used to propagate a normal-conduction hotspot from a gate constriction across and along a portion of the main current-carrying channel. The three-terminal device may be used in various superconducting signal-processing circuitry.

Superconducting three-terminal device and logic gates

A superconducting quantum interference devices (SQUID) comprises a superconducting inductive loop with at least two Josephson junction, whereby a magnetic flux coupled into the inductive loop produces a modulated response up through radio frequencies. Series and parallel arrays of SQUIDs can increase the dynamic range, output, and linearity, while maintaining bandwidth. Several approaches to achieving a linear triangle-wave transfer function are presented, including harmonic superposition of SQUID cells, differential serial arrays with magnetic frustration, and a novel bi-SQUID cell comprised of a nonlinear Josephson inductance shunting the linear coupling inductance. Total harmonic distortion of less than −120 dB can be achieved in optimum cases.

High linearity superconducting radio frequency magnetic field detector

A superconducting integrated circuit, comprising a plurality of superconducting circuit elements, each having a variation in operating voltage over time; a common power line; and a plurality of bias circuits, each connected to the common power line, and to a respective superconducting circuit element, wherein each respective bias circuit is superconducting during at least one time portion of the operation of a respective superconducting circuit element, and is configured to supply the variation in operating voltage over time to the respective superconducting circuit element.

Low-power biasing networks for superconducting integrated circuits

An electronic clock has a single Josephson junction connected in parallel to a resonant circuit, which is a delay line with a matching resistance at the input end to provide series termination. The opposite end of the delay line is an open end to reflect pulses, and the pulse transit time on the line determines the clock rate. A zero crossing detector is provided to initiate the clock operation when an input signal rises above a given threshold, and a reset circuit is included to turn off the clock when the input signal falls below this threshold. A flip-flop circuit allows the clock to be turned on by alternate initiating signal pulses. A modification includes a pulse rejuvenating circuit at the end of the delay line to offset pulse degradation. All of the circuits are fabricated with Josephson junction elements, and the zero crossing detector, reset circuit, flip-flop circuit and pulse rejuvenator circuits include dc-SQUID's. The clock is capable of operation at frequencies up to 100 GHz and can sample input single frequencies as high as 15 GHz.

System and circuits using Josephson junctions

A two-dimensional array of Josephson junctions is used as a high-frequency oscillator capable of emitting coherent power of predetermined frequencies since the geometry of the two-dimensional array allows the individual Josephson junctions to phase lock at predetermined frequencies. The array is controlled at a given voltage and excited by the application of DC current through the array, in effect providing a rapidly tunable DC-to-AC converter at GHz and THz frequencies. The oscillator operates without the application of external high frequency signals or a connection to a cavity resonator. Load matching and other adjustments can be made by selecting the appropriate number of Josephson junctions in the array, selecting a damping factor which determines non-hysteretic operation, adding resistive shunts or a superconducting ground plane. The two-dimensional array used as an oscillator has advantages over one dimensional arrays in that voltage equalization from junction-to-junction occurs naturally so that phase locking is less likely to be affected by non-identical junctions, greater power output can be realized, an output having a narrower line width is produced and impedance matching is relatively easy.

Two-dimensional, Josephson-array, voltage-tunable, high-frequency oscillator

A coherent array of Josephson oscillators is provided Individual hysteresis-free Josephson junctions are longitudinally arranged in a line and have such a spacing as to substantially eliminate quasiparticle interactions To provide a common frequency of operation, equal and opposite dc voltages are produced in adjacent pairs of the Josephson junctions by an arrangement of interlocking dc SQUID's (Superconductive Quantum Interference Device) connected to transversely extending biasing leads Phase coherence for the array is provided by a rf current circulating in an inductive feedback path that loops between the ends of the array

Coherent array of Josephson oscillators with external bias leads

A coherent array of Josephson oscillators is provided. Individual hysteresis-free Josephson junctions are longitudinally arranged in a gap of a central conductor in a line and have such a spacing as to substantially eliminate quasiparticle interactions. To provide a common frequency of operation, equal and opposite dc voltages are produced in adjacent pairs of the Josephson junctions by an arrangement of interlocking dc SQUID's (Superconductive Quantum Interference Device) connected to the longitudinal central conductor using microwave bias tees. Phase coherence for the array is provided by a rf current circulating in an inductive feedback path that loops between the ends of the array.

Transmission line biased coherent array of Josephson oscillators

A method for fabricating indium variable thickness super conducting microbridges uses a single layer of electron resist and EBL to draw a mask which has a gap with a small amount of undercut. A thin layer of material is deposited at normal incidence to form the bridge and material deposited at a sufficiently large oblique angle forms the banks separately. Typical VTB's have bridges 1000 Å thick and <0.4 μm long with the banks 7 μm thick and Rn.sup.˜ 0.1Ω. The method can also form other non-hysteretic weak links such as the SNS junction.

James E. Lukens

Papers

Coherent array of Josephson oscillators with external bias leads

Transmission line biased coherent array of Josephson oscillators

Method for fabricating superconducting weak-links using electron beam lithography