Terahertz time-domain reflectometry was used to monitor the progress of a thermally grown oxide layer and stress-induced, air-filled voids at the interface of an Yttria-stabilized-zirconia ceramic thermal-barrier coating and a metal surface. The thicknesses of these internal layers, observed in scanning-electron-microscope images to increase with thermal-exposure time, have been resolved - even when changing on the order of only a few micrometers - by distinguishing not only increased delays in the arrival times of terahertz pulses reflected from this multilayer structure, but also changes in the width and shape of the pulses. These unique features can be used to predict the lifetime of thermal-barrier coatings and to indicate or warn of spallation conditions. The trends of the experimental results are also confirmed through Fresnel-reflection time-domain simulations.

The stability of entanglement of two atoms in a cavity is analyzed in this work. By studying the general Werner states we clarify the role of Bell-singlet state in the problem of suppression of disentanglement due to spontaneous emission. It is also shown explicitly that the final amount of entanglement depends on the initial ingredients of the Bell-singlet state.PACS numbers: 03.65.Yz 03.65.Ud 03.65.TaOne of the specific features of quantum world is the existence of quantum coherence which forms the basis of describing wide varieties of phenomena including superconductivity and Bose-Einstein condensation of cold atoms. During the last decade, another aspect of quantum coherence, namely, quantum entanglement[1], has been recognized as the essential element of quantum computing [2]. In order to realize quantum information processing, stability of entanglement of quantum subsystems is one of the important problems that requires careful analysis. Instabilities of quantum entanglement can be generated through different mechanisms [3]. In general, an entangled state of a closed system can be disentangled by its own dynamics [4]. On the other hand, due to decoherence, system and environment interaction might not preserve initially entangled state. However, decoherence can also be a dynamical effect if one includes the quantum fluctuation of vacuum. In fact, such fluctuation is the origin of spontaneous emission which can reduce entangled state to separable state via photon emission.The recent work of Yu and Eberly [5] has discussed the finite-time disentanglement via spontaneous emission. In their system two non-interacting atoms are coupled to two separate cavities(environments). As a result, the dynamical evolution of the atoms are independent and, depending on initial state, the effect of spontaneous emission can drive the system to disentangled in finite time. However it is not clear if the disentangle phenomenon will persist if the atoms are allowed to interact. Intuitively, it is easy to imagine that for two atoms interacting in a lossless cavity, the photon emits by one atom during spontaneous emission can be absorbed by the other. As a result, entanglement might be preserved through this mechanism. In fact the above photon process is equivalent to the interaction between atoms by exchanging photon. Furthermore it is also more practical for constructing the quantum circuit inside one cavity instead of distribute the atoms in different separate ones. Consequently, it is inevitable to include the effects of interaction among atoms for any discussions on disentanglement via spontaneous emission. This problem has also been * Electronic address: fmliu@phys.ncku.edu.tw † Electronic address: chiachu@phys.ncku.edu.tw addressed in the interesting work by Tanaś and Ficek[6]. By putting two atoms inside the same cavity they showed that the entanglement exhibits oscillatory behavior, and the amount of entanglement is directly related to the population of the slowly decaying Bell-singlet state in the long time limit. Their ...

Utilizing experimental results, which demonstrate the presence of both Faraday rotation and electric-field-induced linear birefringence in a diluted-magnetic-semiconductor crystal of cadmium manganese telluride (CMT), a single probe that is capable of sensing both electric and magnetic fields independently has been developed. A higher field sensitivity and greater accuracy are observed for the CMT crystal when compared to a lithium tantalate electro-optic crystal and terbium gallium garnet magneto-optic crystal. The linear electro-optic coefficient r41 for CMT has been calculated from electric-field measurements to be 3.5±0.2pm∕V.

A single <110> cadmium-manganese-telluride crystal that exhibits both the Pockels and Faraday effects is used to produce a Poynting-vector sensor for signals in the microwave regime. This multi-birefringent crystal can independently measure either electric or magnetic fields through control of the polarization of the optical probe beam. After obtaining all the relevant electric and magnetic field components, a map of the Poynting vector along a 50-Omega microstrip was experimentally determined without the need for any further transformational calculations. The results demonstrate that this sensor can be used for near-field mapping of the Poynting vector. Utilizing both amplitude and phase information from the fields in the microwave signal, it was confirmed for the case of an open-terminated microstrip that no energy flowed to the load, while for a microstrip with a matched termination, the energy flowed consistently along the transmission line.

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