Coexistence of qubit effects

Two quantum events, represented by positive operators (effects), are coexistent if they can occur as possible outcomes in a single measurement scheme. Equivalently, the corresponding effects are coexistent if and only if they are contained in the ranges of a single (joint) observable. Here we give several equivalent characterizations of coexistent pairs of qubit effects. We also establish the equivalence between our results and those obtained independently by other authors. Our approach makes explicit use of the Minkowski space geometry inherent in the four-dimensional real vector space of selfadjoint operators in a two-dimensional complex Hilbert space

Power and Inefficient Institutions

This paper is concerned with the persistence of inefficient institutions. Why are they not replaced by more effcient ones? What and/or who prevents such change? We provide an answer to these questions based on two key ideas. The principal idea is that institutional change on an issue may adversely affect the bargaining power of some agents on different issues. The second is that certain kinds of frictions (or transaction costs) are present, which do not allow for this deteriorating bargaining power to be compensated for. A key insight obtained from our analysis is that, the greater is the degree of inequality in the players� bargaining powers the more likely it is that ineffcient institutions will persist.

Pairing of a harmonically trapped fermionic Tonks-Girardeau gas

The fermionic Tonks-Girardeau (FTG) gas is a one-dimensional spin-polarized Fermi gas with infinitely strong attractive zero-range odd-wave interactions, arising from a confinement-induced resonance reachable via a three-dimensional p-wave Feshbach resonance. We investigate the off-diagonal long-range order (ODLRO) of the FTG gas subjected to a longitudinal harmonic confinement by analyzing the two-particle reduced density matrix for which we derive a closed-form expression. Using a variational approach and numerical diagonalization we find that the largest eigenvalue of the two-body density matrix is of order N/2, where N is the total particle number, and hence a partial ODLRO is present for a FTG gas in the trap.Comment: 4 pages, 3 figures, revtex

The attitude control of a satellite in an elliptic orbit

Attitude control system for satellite in elliptical orbit calculated by linear equations and computer simulatio

Maintaining Quantum Coherence in the Presence of Noise through State Monitoring

Unsharp POVM measurements allow the estimation and tracking of quantum wavefunctions in real-time with minimal disruption of the dynamics. Here we demonstrate that high fidelity state monitoring, and hence quantum control, is possible even in the presence of classical dephasing and amplitude noise, by simulating such measurements on a two-level system undergoing Rabi oscillations. Finite estimation fidelity is found to persist indefinitely long after the decoherence times set by the noise fields in the absence of measurement.Comment: 5 pages, 4 figure

Decomposition and primary crystallization in undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 melts

Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glasses were prepared by cooling the melt with a rate of about 10 K/s and investigated with respect to their chemical and structural homogeneity by atom probe field ion microscopy and transmission electron microscopy. The measurements on these slowly cooled samples reveal that the alloy exhibits phase separation in the undercooled liquid state. Significant composition fluctuations are found in the Be and Zr concentration but not in the Ti, Cu, and Ni concentration. The decomposed microstructure is compared with the microstructure obtained upon primary crystallization, suggesting that the nucleation during primary crystallization of this bulk glass former is triggered by the preceding diffusion controlled decomposition in the undercooled liquid state

Introduction

Asset management, a distinctive sector within the financial services industry, centers on an agency relationship between a client and an individual manager or firm appointed to manage the client\u27s investment portfolio. Additionally, in many jurisdictions asset managers are subject to a technically complex set of regulatory requirements, which differ across jurisdictions. This book is the only comparative analysis of the law of asset manager liability in the major European jurisdictions, the United States, and Canada, with chapters written by specialists from the relevant jurisdictions plus a comprehensive chapter covering the relevant European law, in particular the MiFID directive. The book\u27s coverage is limited to relationships that pertain to individual portfolios of securities, as opposed to collective investment schemes such as mutual funds and UCITs. A central focus is how regulation interacts with civil liability, whether based on breaches of duties imposed by general law (such as breach of fiduciary duty and duties of care) or on breaches of duties imposed by regulation itself. The Introduction, co-authored by the book\u27s co-editors, situates the country-by-country materials within the broader context of questions about regulatory design and effectiveness. These include whether regulation and liability should be understood as substitutes for each other or as necessary complements; differences in the style of regulation; the role of industry-based self-regulation; and the impact of mandated disclosure of information by asset managers

Quantum Mechanics as a Framework for Dealing with Uncertainty

Quantum uncertainty is described here in two guises: indeterminacy with its concomitant indeterminism of measurement outcomes, and fuzziness, or unsharpness. Both features were long seen as obstructions of experimental possibilities that were available in the realm of classical physics. The birth of quantum information science was due to the realization that such obstructions can be turned into powerful resources. Here we review how the utilization of quantum fuzziness makes room for a notion of approximate joint measurement of noncommuting observables. We also show how from a classical perspective quantum uncertainty is due to a limitation of measurability reflected in a fuzzy event structure -- all quantum events are fundamentally unsharp.Comment: Plenary Lecture, Central European Workshop on Quantum Optics, Turku 2009