Josephson Inductance Research Articles

Limits to the fundamental measurement accuracy in Josephson junction array voltage intercomparisons

The dc voltage output from a hysteretic Josephson junction which is locked to an ac frequency source differs from the ideal Josephson relation if the junction drives a current about a closed superconducting circuit. The difference in voltage ΔV from two hysteretic Josephson junctions driven in series opposition is proportional to the difference in their driving frequencies Δω if the junctions are each biased to the nth voltage step. It is shown here, however, that ΔV is systematically smaller than the voltage difference ΔV0 predicted by the ideal junction relation ΔV0=(nℏ/2e)Δω. If the loop inductance approaches zero, the smallest detectable voltage difference ΔV0 between two junctions is limited by the intrinsic Josephson inductance. For arrays of more than one junction, however, ΔV0 remains proportional to the loop inductance.

High-T/sub c/ superconducting monolithic phase shifter

A high temperature superconducting (HTS) X-band phase shifter using a distributed Josephson inductance (DJI) approach was designed and fabricated. Phase swings of over 60 degrees were measured at 65 K and below, with measurable phase shifts at temperatures above 77 K. High quality HTS films and superconducting quantum interference devices (SQUIDs) were deposited by laser ablation. A total of 40 HTS step edge SQUIDs were successfully integrated into a monolithic HTS circuit to produce a phase shifter in a resonant configuration. The magnitude of the Josephson inductance is calculated and a lumped element model is compared to measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Monolithic high-T/sub c/ superconducting phase shifter at 10 GHz

A monolithic high-temperature-superconductor (HTS) phase shifter integrated into a 10-GHz microstrip line is described. This is the first demonstration of a nonresonant HTS circuit based on a distributed Josephson inductance approach. Phase shifts greater than 150 degrees in resonant structures and 20 degrees in broadband circuits were observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement accuracy of macroscopic quantum circuits with RF-biased Josephson junction arrays

The DC voltage output from a hysteretic Josephson junction which is locked to an AC frequency source differs from the ideal Josephson relation if the junction drives a current about a closed superconducting circuit. The difference in voltage Delta V from two hysteretic Josephson junctions driven in series opposition is proportional to the difference in their driving frequencies Delta omega if the junctions are each biased to the nth voltage step. It is shown here, however, that Delta V is systematically smaller than the voltage difference Delta V0 predicted by the ideal Josephson relation Delta V0=(nh(cross)/2e) Delta omega . If the loop inductance approaches zero, the smallest detectable voltage difference Delta V0 between two junctions is limited by the intrinsic Josephson inductance. For arrays of more than one junction, however, Delta V0 remains proportional to the loop inductance.

Use of the Josephson junction in fundamental quantum electronics experiments

The Josephson junction provides two strong nonlinearities, the Josephson inductance utilized in parametric amplification and the sharp resistive knee used in SIS mixing. Both of these nonlinearities can be strong compared to a characteristic quantum current or voltage scale. This opens the possibility of using Josephson junctions to carry out fundamental experiments in quantum electronics that would be difficult or impossible to carry out at optical frequencies due to the lack of a correspondingly large nonlinearity in optical media. Here we propose a number of such experiments ranging from the generation of squeezed states with Josephson-parametric amplifiers to the generation of quantum-mechanical superpositions of macroscopically distinguishable states via Josephson-transmission lines. How the properties of such states can be investigated using SIS mixers will also be described. Squeezed states may be technologically useful in sensitive and precision measurement. How such states can be used to enhance interferometer sensitivity or reduce noise in phase sensitive measurement will also be described.