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Due to the excellent electromagnetic properties of superconductor materials, superconducting generators have higher efficiency, lower weight and volume than traditional rotating machines. However, it is difficult to simulate the electromagnetic behavior in the superconducting generator due to the nonlinear E–J relationship. A numerical model based on the T–A formulation and moving mesh method is adopted to simulate the superconducting rotating machine, and the electromagnetic and mechanical behaviors of the superconducting rotating machine are investigated. The fully superconducting generator investigated in this article is radial type, which consists of field windings and armature windings made from YBa2Cu3O7−Δ (YBCO) superconducting race-track coils. The anisotropic field-dependent critical current density and the E–J power law relationship are considered in our model. The “virtual tape” model is introduced to calculate the induced current in the T–A formulation. The numerical results are obtained by the finite element method. The electromagnetic results calculated by our model are compared with results from the H–A formulation. The ac losses and stress distributions in superconducting coils are presented based on the T–A formulation. The results show that the body force and stress are periodic, and the stress will concentrate on the boundary of the coil. The magnetic field in the rotor is larger than that in the stator, and the field windings suffer greater body force and stress than the armature windings. This model has acceptable relative error with the H–A model for the time saved following T–A approach and relevance to mechanical calculations. Thus, this model can aid the design of superconducting rotating machines. [ABSTRACT FROM AUTHOR]

AC loss has become a key problem for practical applications of high-temperature superconductors. It is well known that mechanical deformation will affect the critical current and ac loss as the superconductor is subjected to the magnetic field or transport current. In this paper, the ac losses in Bi2Cr2Ca2Cu 3O10 (Bi2223)/Ag tapes under bending deformation are investigated. Bi2223 tape consists of Ag matrix and Bi2223 filaments, and the ac losses are generated by transport current and external field. By considering the plastic deformation of Ag matrix and residual strain, the simplified mechanical fracture model is established. Then, the finite element method analysis is used to investigate the relation of critical current and ac loss with bending deformations, and the losses are presented for different transport current and external magnetic field conditions. The influences of filament fracture on the ac loss are discussed for transport current and external magnetic field cases, respectively. [ABSTRACT FROM PUBLISHER]

From microwave and resonant tunneling spectroscopy measurements we independently obtained all device parameters needed to reconstruct the Hamiltonian of an rf-SQUID flux qubit. Energy relaxation of the qubit as a function of flux bias and temperature was investigated experimentally. It is found that the energy relaxation rate at different flux biases scales to a universal temperature dependence. This universal T-dependence of T1 time agrees well with a theoretical model in which the thermal equilibrium population of the excited states is considered. [ABSTRACT FROM AUTHOR]

The flux state quantum bit (qubit) is promising for a solid state implementation of scalable quantum computing. The simplest flux state qubit consists of an rf SQUID with two fluxoid states, which can be readout with a dc SQUID—the most sensitive magnetic flux detector. Efficient readout with less back-action is desirable for quantum computing. In this work, we report measurements of the switching flux and switching current distributions of under damped dc SQUIDs. The data show that single shot readout of flux qubit with very high efficiency (>99%) can be realized using underdamped hysteretic dc SQUIDs. [ABSTRACT FROM AUTHOR]

Rabi oscillation between macroscopic quantum states of superconducting devices has important implications to the foundations of quantum mechanics as well as the development of quantum computing. At low temperature and low damping, a Josephson tunnel junction biased slightly below its critical current constitutes a macroscopic two-level quantum system. Here we report the results of a single-qubit rotation experiment in a NbN/AIN/NbN Josephson tunnel junction. We show that the state of the junction qubit can be controlled by varying the duration of the microwave pulses. [ABSTRACT FROM AUTHOR]