I–V Characteristic and Josephson inductance of ultra-long intrinsic Josephson junction arrays
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Kinetic inductance
Vicinal
Superconducting tunnel junction
The device that is the workhorse of most superconducting computers is the Josephson Junction, which consists of two superconducting regions separated by a non-superconducting layer—usually an insulator. In this chapter, the authors begin with a basic discussion of tunneling. They use a phenomenological approach to model the coupling between the superconductors in a Josephson junction resulting from the tunneling of Cooper pairs. A qubit can also be formed by placing two Josephson junctions in parallel. This configuration is referred to as a Superconducting Quantum Interference Device, or SQUID. By biasing the Josephson junction with different currents, it can also be used to realize a time-varying inductance that is used in low noise parametric amplifiers. Finally, when two junctions are placed in parallel, the effective inductance can be varied by the application of a magnetic field. This makes it possible to realize tunable qubits.
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Abstract We discuss the prospect of using quantum properties of large scale Josephson junction arrays for quantum manipulation and simulation. We study the collective vibrational quantum modes of a Josephson junction array and show that they provide a natural and practical method for realizing a high quality cavity for superconducting qubit based QED. We further demonstrate that by using Josephson junction arrays we can simulate a family of problems concerning spinless electron–phonon and electron–electron interactions. These protocols require no or few controls over the Josephson junction array and are thus relatively easy to realize given currently available technology.
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Charge qubit
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Kinetic inductance
Vicinal
Superconducting tunnel junction
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Superconducting tunnel junction
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The Hamiltonian of a superconducting thin loop interrupted by a double-barrier Josephson junction is derived. The parameter ε, which takes account of the difference in the Josephson coupling of the two single junctions in the SISIS structure, is seen to allow variation of the energy gap ΔE01 between the ground state and the first excited flux number state of the system. An additional parameter γ, describing the coupling between the outer electrodes of the double-barrier Josephson junction, is introduced. Persistent currents in the system are studied in terms of the usual parameter α, representing the ratio between the Josephson energy and the magnetic energy, and of the externally applied flux.
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Theoretical analysis is carried out on a super-super-super tunnelling structure with double barriers between the sandwiched thin superconducting layer and the two bulk superconductors on either side. The equivalent circuit of this structure is found to be a Josephson junction in parallel with two series-connected Josephson junctions. The function of this device as a memory element is discussed.
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This thesis presents experimental research on Josephson junction devices that behave quantum mechanically. The devices are formed by micrometer-sized superconducting islands, that are interconnected by a Josephson tunnel junction: a thin insulating layer between two superconductors. With current microfabrication technology it is possible to make very clean and well-defined junctions. The research that is presented in this thesis aimed at investigating whether Josephson junction circuits can have quantum coherent dynamics with a long decoherence time.
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The dynamics of fluxons in long Josephson junctions is a well-known example of soliton physics and allows for studying highly nonlinear relativistic electrodynamics on a microscopic scale. Such fluxons are supercurrent vortices that can be accelerated by bias current up to the Swihart velocity, which is the characteristic velocity of electromagnetic waves in the junction. We experimentally demonstrate slowing down relativistic fluxons in Josephson junctions whose bulk superconducting electrodes are replaced by thin films of a high kinetic inductance superconductor. Here, the amount of magnetic flux carried by each supercurrent vortex is significantly smaller than the magnetic flux quantum Φ0. Our data show that the Swihart velocity is reduced by about one order of magnitude compared to conventional long Josephson junctions. At the same time, the characteristic impedance is increased by an order of magnitude, which makes these junctions suitable for a variety of applications in superconducting electronics.
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Superconducting closed loops composed of N series Josephson junctions are discussed. The conditions to achieve the n quantum state of a fluxoid in the loop are analyzed. It is found that the n quantum state exists in Josephson loops having more than 4n pieces of junctions even if it is assumed that the inductance L in the loop is negligibly small. This n quantum state is achieved by an asymmetric current feed to the Josephson loop. The properties of the loop are easily explained by using a pendulum analog.
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