[PDF] Macroscopic Quantum Tunneling In Long Josephson Junctions eBook

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Page : 171 pages
File Size : 35,16 MB
Release : 1991
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Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q (almost equal to) 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement.

Author : C Giovannella
Publisher : World Scientific
Page : 410 pages
File Size : 41,59 MB
Release : 1995-11-16
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ISBN : 9814548898

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This volume is a review on the recent progresses done in the understanding of the physics of the superconducting arrays. It consists of five sessions:All the topical contributions go well beyond those characteristics of the condensed matter physics and offer links to the domains of the nonlinear science, complex systems and statistical mechanics.

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Page : 19 pages
File Size : 40,53 MB
Release : 1993
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This research consisted of studies of the fundamentals and applications of long Josephson Junctions and very small junctions, all fabricated out of NbN. We have developed technology for fabricating by reactive sputtering high quality long Josephson junctions with current densities of 100- 1,000 A/sq cm Such junctions were used for studies of giant steps on the I-V curve caused by fluxon pinning and of macroscopic quantum tunneling down to 15 mK. A new system, a long Josephson junction biased at Fiske steps, is presented for studies of Macroscopic Quantum Tunneling. Our results show applications of fluxons in long Josephson junctions for Fluxon Oscillator, Voltage Standard, and for observing Macroscopic Coherent Tunneling. We, have also studied very small NbN junctions fabricated with a STM where single electron tunneling is observed. We were the first to present such tunneling at room temperature; this is important for applications. Students and postdoctoral fellows were involved in this research.

Author : Wildermuth, Matthias Micha
Publisher : KIT Scientific Publishing
Page : 160 pages
File Size : 10,77 MB
Release : 2023-09-11
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ISBN : 373151303X

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In the last decades, superconducting devices have emerged as a promising platform for quantum technologies, including quantum sensing and quantum computing. Their key elements are Josephson junctions, which allow for coherent supercurrent tunneling between two weakly linked superconductors. If such a junction is extended in one direction to a long junction, the superconducting phase difference can vary in space and time and may allow for quantized phase windings that drive supercurrent vortices.