Strong coupling of a qubit to shot noise

We perform a nonperturbative analysis of a charge qubit in a double quantum dot structure coupled to its detector. We show that strong detector-dot interaction tends to slow down and halt coherent oscillations. The transitions to a classical and a low-temperature quantum overdamping (Zeno) regime are studied. In the latter, the physics of the dissipative phase transition competes with the effective shot noise.Comment: 5 pages, 4 figure

Exotic composites: the decay of deficit angles in global-local monopoles

We study static, spherically symmetric, composite global-local monopoles with a direct interaction term between the two sectors in the regime where the interaction potential is large. At some critical coupling the global defect disappears and with it the deficit angle of the space-time. We find new solutions which represent local monopoles in an Anti-de-Sitter spacetime. In another parameter range the magnetic monopole, or even both, disappear. The decay of the magnetic monopole is accompanied by a dynamical transition from the higgsed phase to the gauge-symmetric phase. We comment on the applications to cosmology, topological inflation and braneworlds.Comment: 17 pages, 11 figures; Minor corrections, matches published versio

Vector magnetometer design study: Analysis of a triaxial fluxgate sensor design demonstrates that all MAGSAT Vector Magnetometer specifications can be met

The design of the vector magnetometer selected for analysis is capable of exceeding the required accuracy of 5 gamma per vector field component. The principal elements that assure this performance level are very low power dissipation triaxial feedback coils surrounding ring core flux-gates and temperature control of the critical components of two-loop feedback electronics. An analysis of the calibration problem points to the need for improved test facilities

No spin-glass transition in the "mobile-bond" model

The recently introduced ``mobile-bond'' model for two-dimensional spin glasses is studied. The model is characterized by an annealing temperature T_q. On the basis of Monte Carlo simulations of small systems it has been claimed that this model exhibits a non-trivial spin-glass transition at finite temperature for small values of T_q. Here the model is studied by means of exact ground-state calculations of large systems up to N=256^2. The scaling of domain-wall energies is investigated as a function of the system size. For small values T_q<0.95 the system behaves like a (gauge-transformed) ferromagnet having a small fraction of frustrated plaquettes. For T_q>=0.95 the system behaves like the standard two-dimensional +-J spin-glass, i.e. it does NOT exhibit a phase transition at T>0.Comment: 4 pages, 5 figures, RevTe

Measurable Consequences of the Local Breakdown of the Concept of Temperature

Local temperature defined by a local canonical state of the respective subsystem, does not always exist in quantum many body systems. Here, we give some examples of how this breakdown of the temperature concept on small length scales might be observed in experiments: Measurements of magnetic properties of an anti-ferromagnetic spin-1 chain. We show that those magnetic properties are in fact strictly local. As a consequence their measurement reveals whether the local (reduced) state can be thermal. If it is, a temperature may be associated to the measurement results, while this would lead to inconsistencies otherwise.Comment: some comments added, results remain unchange

Prognostic factors in seminomas with special respect to HCG: Results of a prospective multicenter study

Objective: In a prospective multicenter trial, it was our intention to elucidate clinical prognostic factors of seminomas with special reference to the importance of human chorionic gonadotropin (HCG) elevations in histologically pure seminomas. Methods: Together with 96 participating urological departments in Germany, Austria, and Switzerland, we recruited 803 seminoma patients between 1986 and 1991. Out of 726 evaluable cases, 378 had elevated, while 348 had normal HCG values in the cubital vein. Histology was reviewed by two reference pathologists. HCG levels were determined in local laboratories and in a study laboratory. Standard therapy was defined as radiotherapy in stages I (30 Gy) and IIA/B (36 Gy) to the paraaortal and the ispilateral (stage I) and bilateral (stage IIA/B) iliac lymph nodes; higher stages received polychemotherapy and surgery in case of residual tumor masses. Statistics included chi-square tests, linear Cox regression, and log-rank test. Results: The HCG elevation is associated with a larger tumor mass (primary tumor and/or metastases). HCG-positive and HCG-negative seminomas had no different prognostic outcome after standard therapy. The overall relapse rate of 6% and the survival rate of 98% after 36 months (median) indicate an excellent prognosis. The calculation of the relative risk of developing a relapse discovered only stage of the disease and elevation of the lactate dehydrogenase concentration and its prolonged marker decay as independent prognostic factors for seminomas. A more detailed analysis of the prognostic significance of the stage revealed that the high relapse rate in stage IIB seminomas after radiotherapy (24%) is responsible for this result. Conclusions: We conclude that HCG-positive seminomas do not represent a special entity. Provided standard therapy is applied, HCG has no influence on the prognosis. Patients with stage IIB disease should be treated with chemotherapy because of the demonstrated higher relapse rate outside the retroperitoneum. Copyright (C) 1999 S. Karger AG. Basel

Lower Critical Dimension of Ising Spin Glasses

Exact ground states of two-dimensional Ising spin glasses with Gaussian and bimodal (+- J) distributions of the disorder are calculated using a ``matching'' algorithm, which allows large system sizes of up to N=480^2 spins to be investigated. We study domain walls induced by two rather different types of boundary-condition changes, and, in each case, analyze the system-size dependence of an appropriately defined ``defect energy'', which we denote by DE. For Gaussian disorder, we find a power-law behavior DE ~ L^\theta, with \theta=-0.266(2) and \theta=-0.282(2) for the two types of boundary condition changes. These results are in reasonable agreement with each other, allowing for small systematic effects. They also agree well with earlier work on smaller sizes. The negative value indicates that two dimensions is below the lower critical dimension d_c. For the +-J model, we obtain a different result, namely the domain-wall energy saturates at a nonzero value for L\to \infty, so \theta = 0, indicating that the lower critical dimension for the +-J model exactly d_c=2.Comment: 4 pages, 4 figures, 1 table, revte