Dynamics of superconducting qubits with exactly solvable bias pulses

The dynamics of a quantum two-state system (qubit) with external control bias pulses of special shapes is considered. The bias pulses represent the potentials for which the Schrödinger equation can be solved exactly. The probability to register a definite direction of the current in a loop and its time-averaged values are calculated for the flux qubit; calculations are performed both analytically and numerically in the presence of relaxation and decoherence within the framework of the density matrix formalism. It is demonstrated that there exist external bias pulses for which the definite current direction probability is a monotonically increasing function of time that approaches a limiting value exceeding 1/2. The probability to find the system in the excited state is calculated, and the possibility of inverse population in a properly driven two-state system is demonstrated given that the relaxation and decoherence rates are small enough.     

Nature of low-energy dipole strength in nuclei: the case of a resonance at particle threshold in 208Pb

A high-resolution (gamma,gamma') study of the electric dipole response in 208Pb at the S-DALINAC reveals a resonance structure centered around the neutron emission threshold. Microscopic quasiparticle phonon model calculations in realistic model spaces including the coupling to complex configurations are able to describe the data in great detail. The resonance is shown to result from surface density oscillations of the neutron skin relative to an approximately isospin-saturated core. It also forms an integral part of a toroidal E1 mode representing an example of vortex collective motion in nuclei.     

Application of the method of straight lines to determining the stressed-strained state and dynamic characteristics of a hollow noncircular cylinder

Using the method of straight lines, problems of elasticity theory for a noncircular hollow cylinder are investigated. By means of separation of variables along the generatrix and finite-difference approximation across the thickness, the input partial differential equations are reduced to a system of ordinary differential equations, which is solvable by the stable numerical method of discrete orthogonalization. Specific features of application of the method proposed to static and dynamic problems of a hollow noncircular cylinder are illustrated by way of examples. Bibliography: 5 titles. Translated from,Obchyslyuval’na ta Prykladna Matematyka, No. 76, 1992, pp. 89–87.     

Reconfigurable atom chip on a transparent ferrite-garnet film

We introduce a new choice of material for the creation of microscopic magnetic potentials for the trapping and guiding of ultracold neutral atoms. The potentials are created above a ferrimagnetic, transparent (BiYTmGd)₃(FeGa)₅O₁₂ film by patterning the magnetic-domain structure in the film with a magneto-optical recording method. Patterns with linewidth down to 2 μm have been achieved, enabling trap frequencies of the order of 100 kHz for ⁸⁷Rb atoms in the state |F=1, m_F=-1〉. The main advantages of the material are: 1) magnetic-field noise is suppressed due to the dielectricity of the material and the absence of electric currents, 2) trapped atoms can be addressed optically through the transparent film, and 3) the film can be repatterned, which enables different experiments with the same component.