Improved numerical methods for infinite spin chains with long-range interactions

We present several improvements of the infinite matrix product state (iMPS) algorithm for finding ground states of one-dimensional quantum systems with long-range interactions. As a main new ingredient we introduce the superposed multi-optimization (SMO) method, which allows an efficient optimization of exponentially many MPS of different length at different sites all in one step. Hereby the algorithm becomes protected against position dependent effects as caused by spontaneously broken translational invariance. So far, these have been a major obstacle to convergence for the iMPS algorithm if no prior knowledge of the systems translational symmetry was accessible. Further, we investigate some more general methods to speed up calculations and improve convergence, which might be partially interesting in a much broader context, too. As a more special problem, we also look into translational invariant states close to an invariance braking phase transition and show how to avoid convergence into wrong local minima for such systems. Finally, we apply the new methods to polar bosons with long-range interactions. We calculate several detailed Devil's Staircases with the corresponding phase diagrams and investigate some supersolid properties.Comment: Main text: 17 pages plus references, 8 figures. Supplementary info: 6 pages. v2: improved presentation and more results adde

Geometric phase gate on an optical transition for ion trap quantum computation

We propose a geometric phase gate of two ion qubits that are encoded in two levels linked by an optical dipole-forbidden transition. Compared to hyperfine geometric phase gates mediated by electric dipole transitions, the gate has many interesting properties, such as very low spontaneous emission rates, applicability to magnetic field insensitive states, and use of a co-propagating laser beam geometry. We estimate that current technology allows for infidelities of around 10$^{-4}$.Comment: 4 pages, 2 figure

1005-81 Myocardial Protection by Na+/H+ Exchange Inhibition in Ischemic, Reperfused Porcine Hearts

The protective effect of the Na+/H+ exchange inhibitor HOE 694 was tested in porcine hearts subjected to 45min of regional ischemia and 24 h of reperfusion. The compound (3mg/kg) was intravenously injected in 6 pigs each either 10 min before ischemia (group A) or 10 min before reperfusion (group B). Six animals served as controls. Apart from the main end-points, infarct size and regional systolic shortening, the effect of HOE 694 on global hemodynamic parameters which included coronary blood flow and coronary venous oxygen saturation was evaluated. Although the Na+IH+ exchange inhibitor did not affect global hemodynamics, preischemic treatment with HOE 694 decreased infarct size from 65±18% (control group) to 12 ± 9% (p < 0.01) and improved systolic shortening from 8 ± 6% (control group) to 28 ± 9% P < 0.02). In addition, increase in heart rate and myocardial contracture during early reperfusion were significantly attenuated in group A. Treatment of group B did not exhibit protective effects.ConclusionNa+/H+ exchange inhibition is a very protective means in myocardial ischemia and reperfusion when administered before ischemia. In this model, it was ineffective when given before reperfusion

General solution for the complex frequency shift in microwave measurements of thin films

Perturbation of a microwave cavity by a small sample with variable dielectric, magnetic, or conducting properties is considered. The complex frequency shift is derived in terms of a volume integral, or equivalently, in terms of a surface integral. These are used to obtain a general formula for thin films in the microwave electric field maximum. The complex frequency shift depends on the depolarization factor of the film and on its thickness in a nontrivial way. The previously known expressions for the complex frequency shift are shown to be good approximations of the present solution in the low and high conductivity limits. Our formula is applied to calculate the signal shapes in superconducting films of various geometric parameters and conductivities. It is shown that a diversity of signal shapes can result, and experimental support of those shapes is provided. The role of the dielectric substrate on which the thin film is grown is simply reduced to an asymmetry effect

Microwave response of thin niobium films under perpendicular static magnetic fields

The microwave response of high quality niobium films in a perpendicular static magnetic field has been investigated. The complex frequency shift was measured up to the upper critical fields. The data have been analyzed by the effective conductivity model for the type-II superconductors in the mixed state. This model is found to yield consistent results for the coherence lengths in high-kappa superconducting samples, and can be used with HTSC even at temperatures much below T_c. It is shown that for samples with high values of depinning frequency, one should measure both components of the complex frequency shift in order to determine the flow resistivity. The thick Nb film (160 nm) has low resistivity at 10 K, comparable to the best single crystals, and low kappa value. In contrast, the thinnest (10 nm) film has kappa ~ 9.5 and exhibits a high depinning frequency (~20 GHz). The upper critical field determined from microwave measurements is related to the radius of nonoverlaping vortices, and appears to be larger than the one determined by the transition to the normal state.Comment: 8 pages, 7 figures; submitted to PRB; measured rho_n; changes due to the referees' comments (abstract, conclusions, extended introduction