Macroscopic limit of a solvable dynamical model

The interaction between an ultrarelativistic particle and a linear array made up of $N$ two-level systems (^^ ^^ AgBr" molecules) is studied by making use of a modified version of the Coleman-Hepp Hamiltonian. Energy-exchange processes between the particle and the molecules are properly taken into account, and the evolution of the total system is calculated exactly both when the array is initially in the ground state and in a thermal state. In the macroscopic limit ($N \rightarrow \infty$), the system remains solvable and leads to interesting connections with the Jaynes-Cummings model, that describes the interaction of a particle with a maser. The visibility of the interference pattern produced by the two branch waves of the particle is computed, and the conditions under which the spin array in the $N \rightarrow \infty$ limit behaves as a ^^ ^^ detector" are investigated. The behavior of the visibility yields good insights into the issue of quantum measurements: It is found that, in the thermodynamical limit, a superselection-rule space appears in the description of the (macroscopic) apparatus. In general, an initial thermal state of the ^^ ^^ detector" provokes a more substantial loss of quantum coherence than an initial ground state. It is argued that a system decoheres more as the temperature of the detector increases. The problem of ^^ ^^ imperfect measurements" is also shortly discussed.Comment: 30 pages, report BA-TH/93-13

Einstein-Podolsky-Rosen-like correlation on a coherent-state basis and inseparability of two-mode Gaussian states

The strange property of the Einstein-Podolsky-Rosen (EPR) correlation between two remote physical systems is a primitive object on the study of quantum entanglement. In order to understand the entanglement in canonical continuous-variable systems, a pair of the EPR-like uncertainties is an essential tool. Here, we consider a normalized pair of the EPR-like uncertainties and introduce a state-overlap to a classically correlated mixture of coherent states. The separable condition associated with this state-overlap determines the strength of the EPR-like correlation on a coherent-state basis in order that the state is entangled. We show that the coherent-state-based condition is capable of detecting the class of two-mode Gaussian entangled states. We also present an experimental measurement scheme for estimation of the state-overlap by a heterodyne measurement and a photon detection with a feedforward operation.Comment: 9 pages, 5 figures. A part of the materials in Sec. VI B of previous versions was moved into another paper: Journal of Atomic, Molecular, and Optical Physics, 2012, 854693 (2012). http://www.hindawi.com/journals/jamop/2012/854693

Exponential behavior of a quantum system in a macroscopic medium

An exponential behavior at all times is derived for a solvable dynamical model in the weak-coupling, macroscopic limit. Some implications for the quantum measurement problem are discussed, in particular in connection with dissipation.Comment: 8 pages, report BA-TH/94-17

Dynamical Semigroup Description of Coherent and Incoherent Particle-Matter Interaction

The meaning of statistical experiments with single microsystems in quantum mechanics is discussed and a general model in the framework of non-relativistic quantum field theory is proposed, to describe both coherent and incoherent interaction of a single microsystem with matter. Compactly developing the calculations with superoperators, it is shown that the introduction of a time scale, linked to irreversibility of the reduced dynamics, directly leads to a dynamical semigroup expressed in terms of quantities typical of scattering theory. Its generator consists of two terms, the first linked to a coherent wavelike behaviour, the second related to an interaction having a measuring character, possibly connected to events the microsystem produces propagating inside matter. In case these events breed a measurement, an explicit realization of some concepts of modern quantum mechanics ("effects" and "operations") arises. The relevance of this description to a recent debate questioning the validity of ordinary quantum mechanics to account for such experimental situations as, e.g., neutron-interferometry, is briefly discussed.Comment: 22 pages, latex, no figure

Anomalous Anisotropic Magnetoresistance in Heavy-Fermion PrFe4P12

We have investigated the anisotropy of the magnetoresistance in the Pr-based HF compound PrFe4P12. The large anisotropy of effective mass and its strong field dependence have been confirmed by resistivity measurements. Particularly for H||[111], where the effective mass is most strongly enhanced, the non-Fermi liquid behavior has been observed. Also, we have found the angular dependence of the magnetoresistance sharply enhanced at H||[111], which is evidently correlated with both the non-Fermi liquid behavior and the high-field ordered state (B-phase).Comment: 3 pages, 3 figures. J. Phys. Soc. Jpn. Vol.77, No.8, in pres

Non-Equilibrium Ionization States of GRB Environments

Iron spectral features are thought to be the best tracer of a progenitor of gamma-ray bursts (GRBs). The detections of spectral features such as an iron line and/or a Radiative Recombination edge and Continuum (RRC) were reported in four X-ray afterglows of GRBs. However their properties were different each other burst by burst. For example, Chandra observation of GRB 991216 reported both the strong H-like iron line together with its RRC. On the contrary, Yoshida et al. (2001) report only a detection of the strong RRC in GRB 970828 with ASCA. Since it is difficult to produce the strong RRC, we have to consider special condition for the line and/or the RRC forming region. In this paper, we point out a possibility of a ``non-equilibrium ionization state'' for the line and the RRC forming region.Comment: 10pages, 2figures. Accepted for ApJL. This is a companion paper by A.Yoshida et. a