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Josephson 50th Anniversary - Special Session at Applied Superconductivity Conference 2012 (ASC 2012)

The Josephson Effect: Brian Josephson Debates John Bardeen

Presenter: Dr. Don McDonald

Mathematics versus intuition, the vitality of youth versus prestige and maturity; that was the essence of the spectacle of the debate between the graduate student and the Nobel Laureate when Josephson and Bardeen faced-off in London in 1962. Josephson was fascinated by the reality of the phase in the wavefunction of superconductivity, as demonstrated by magnetic flux quantization; could there be other manifestations of the phase? He was intrigued by a Cohen, Falicov, and Phillips paper on tunneling theory and quickly set about applying it to superconductors. At the time the prevailing view in his laboratory, as expressed by his graduate adviser Brian Pippard, was that a single electron had a low probability of tunneling; thus two electrons tunneling simultaneously would be rare indeed. Surprisingly, Josephson’s mathematics told him otherwise. Bardeen argued that the math was wrong. Shortly thereafter, experiments by Philip Anderson and John Rowell decided the issue in favor of Josephson; for tunneling, mathematics beat intuition.

The Josephson Effect: The Observations of Josephson's Effects

Presenter: Dr. John M. Rowell

Brian Josephson’s predictions, made in 1962, that both direct and alternating supercurrents flow through a tunnel barrier between two superconducting films were confirmed experimentally in 1963. Electron tunneling in such junctions had been reported in 1960 by Giaever and the group at A. D. Little. Using copies of entries in my Bell Labs notebooks, I will show how, in a collaboration with P. W. Anderson, the direct supercurrent and its dependence on small magnetic fields was observed in January 1963. The alternating supercurrent was observed by S. Shapiro a few months later. Early in 1964, following experiments by R. D. Parks and J. M. Mochel, Anderson extended the Josephson Effects from tunnel junctions to weak superconducting links

The Josephson Effect: The Original SQUIDs

Presenter: Dr. Arnold H. Silver

The first experiments demonstrating macroscopic quantum interference in superconductors were performed in 1962 and 1963 at the Ford Motor Company Scientific Laboratory as the analog of two-slit interference. Three pioneering experiments, imbedding two Josephson tunnel junctions in thin film multiply connected superconducting circuits, illustrated: two-junction interference superimposed on single junction Fraunhofer diffraction, the Aharonov-Bohm effect of a vector potential in a magnetic field-free region, and Kinetic inductance in thin superconducting films via superconducting pair de-Broglie waves. These experiments followed some unusual microwave observations in superconductors and the demonstrations of flux quantization in superconductors and the Josephson junction. Following these experiments, our efforts shifted to bulk niobium structures using “point-contact” junctions as prototype Josephson junctions, resulting in the invention of the dc (two-junction) and rf (one-junction) Superconducting Quantum Interference Devices, which we named SQUIDs. I will present a first-hand account of the unique sequence of events that led to these discoveries and inventions.



The Josephson Effect: SQUIDs Then and Now: From SLUGS to Axions

Presenter: Prof. John Clarke

In 1964, Jaklevic, Lambe, Silver and Mercereau demonstrated quantum interference in a superconducting ring containing two Josephson tunnel junctions. The following year saw the appearance of the SLUG (Superconducting Low-inductance Undulatory Galvanometer)_a blob of solder frozen around a length of niobium wire_that was used as a voltmeter with femtovolt resolution. Although primitive by today’s standards, the SLUG was used successfully in a number of ultrasensitive experiments, including a comparison of the Josephson voltage-frequency relation in different superconducting materials and the detection of charge imbalance in superconductors. A full theory of the dc SQUID (Superconducting QUantum Interference Device) appeared in 1977. Today, the square washer dc SQUID with an integrated input coil finds a wide range of applications. SQUIDs are used in a variety of configurations_for example, magnetometers, gradiometers, low-frequency and microwave amplifiers, and susceptometers_in applications including magnetoencephalography, magnetocardiography, geophysics, nondestructive evaluation, standards, cosmology, reading out superconducting quantum bits, and a myriad of one-of-a-kind experiments in basic science. Experiments are described to hunt for the axion_a candidate for cold dark matter_ and to perform magnetic resonance imaging in microtesla magnetic fields.

The Josephson Effect: The Josephson Volt

Presenter: Dr. Richard Kautz

In 1962 Brian Josephson predicted that a superconducting tunnel junction subjected to microwave radiation of frequency f will produce voltages quantized in units of hf/2e, where h is the Planck constant and e is the elementary charge. This ac Josephson effect was of immediate interest to metrology, because it relates voltage (a poorly known quantity) to frequency (known to high accuracy) through two fundamental constants. The basic effect was verified experimentally by Sidney Shapiro, and the predicted quantization was subsequently shown to be of metrological accuracy by Don Langenberg and collaborators, among others. Thus, in 1972 the ac Josephson effect was adopted internationally as a practical standard of voltage, becoming the first quantum electrical standard. Today, series arrays including as many as 300,000 Josephson junctions produce quantized dc voltages well in excess of 10 V and are used in measurement laboratories around the world. In addition, pulse-driven junction arrays have been used to generate highly accurate ac waveforms. The metrological community now anticipates that the Josephson volt and the quantum Hall resistance will soon lead to a redefinition of the SI units that eliminates the kilogram as a base unit and rids the system of its last remaining artifact standard.

The Josephson Effect: Josephson Digital Electronics in the Soviet Union

Presenter: Prof. Konstantin K. Likharev

I will present a brief review of the work on superconducting digital electronics, based on the Josephson effect, in the former Soviet Union - from 1967 to 1991. The research efforts by several academic and industrial groups included the catch-up work on latching logic and memory, original design of non-latching Josephson cryotrons, and the conceptual development of single-flux-quantum devices circuits. The latter work has eventually led to the invention of reversible parametric-quantron circuits in 1975, and ultrafast RSFQ logic in 1985.