Generalized reduction formula for Discrete Wigner functions of multiqubit systems

Density matrices and Discrete Wigner Functions are equally valid representations of multiqubit quantum states. For density matrices, the partial trace operation is used to obtain the quantum state of subsystems, but an analogous prescription is not available for discrete Wigner Functions. Further, the discrete Wigner function corresponding to a density matrix is not unique but depends on the choice of the quantum net used for its reconstruction. In the present work, we derive a reduction formula for discrete Wigner functions of a general multiqubit state which works for arbitrary quantum nets. These results would be useful for the analysis and classification of entangled states and the study of decoherence purely in a discrete phase space setting and also in applications to quantum computingComment: 7 Pages and zero figure

Spin flip of multiqubit states in discrete phase space

Time reversal and spin flip are discrete symmetry operations of substantial import to quantum information and quantum computation. Spin flip arises in the context of separability, quantification of entanglement and the construction of Universal NOT gates. The present work investigates the relationship between the quantum state of a multiqubit system represented by the Discrete Wigner Function (DWFs) and its spin-flipped counterpart. The two are shown to be related through a Hadamard matrix that is independent of the choice of the quantum net used for the tomographic reconstruction of the DWF. These results would be of interest to cases involving the direct tomographic reconstruction of the DWF from experimental data and in the analysis of entanglement related properties purely in terms of the Discrete Wigner function

Hidden Markov models for the activity profile of terrorist groups

The main focus of this work is on developing models for the activity profile of a terrorist group, detecting sudden spurts and downfalls in this profile, and, in general, tracking it over a period of time. Toward this goal, a $d$-state hidden Markov model (HMM) that captures the latent states underlying the dynamics of the group and thus its activity profile is developed. The simplest setting of $d=2$ corresponds to the case where the dynamics are coarsely quantized as Active and Inactive, respectively. A state estimation strategy that exploits the underlying HMM structure is then developed for spurt detection and tracking. This strategy is shown to track even nonpersistent changes that last only for a short duration at the cost of learning the underlying model. Case studies with real terrorism data from open-source databases are provided to illustrate the performance of the proposed methodology.Comment: Published in at http://dx.doi.org/10.1214/13-AOAS682 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Towards Low-Threshold, Real-Time Solar Neutrino Detectors

We discuss an alternative approach to the detection of solar neutrinos using a coarsely segmented detector based on inverse-beta decay onto $^{160}$Gd or $^{176}$Yb. While it is know that similar approaches, already discussed in the literature, can in principle provide low-threshold, real-time energy spectroscopy with intrinsic background rejection features, the concepts presented here make this scheme possible with lower background and current technology.Comment: 10 pages, 2 figure

Development of a Gd Loaded Liquid Scintillator for Electron Anti-Neutrino Spectroscopy

We report on the development and deployment of 11.3 tons of 0.1% Gd loaded liquid scintillator used in the Palo Verde reactor neutrino oscillation experiment. We discuss the chemical composition, properties, and stability of the scintillator elaborating on the details of the scintillator preparation crucial for obtaining a good scintillator quality and stability.Comment: 9 pages, 4 figures, submitted to NIM