Entropy Distance: New Quantum Phenomena

We study a curve of Gibbsian families of complex 3x3-matrices and point out new features, absent in commutative finite-dimensional algebras: a discontinuous maximum-entropy inference, a discontinuous entropy distance and non-exposed faces of the mean value set. We analyze these problems from various aspects including convex geometry, topology and information geometry. This research is motivated by a theory of info-max principles, where we contribute by computing first order optimality conditions of the entropy distance.Comment: 34 pages, 5 figure

Disordered hyperuniformity in two-component non-additive hard disk plasmas

We study the behavior of a two-component plasma made up of non-additive hard disks with a logarithmic Coulomb interaction. Due to the Coulomb repulsion, long-wavelength total density fluctuations are suppressed and the system is globally hyperuniform. Short-range volume effects lead to phase separation or to hetero-coordination for positive or negative non-additivities, respectively. These effects compete with the hidden long-range order imposed by hyperuniformity. As a result, the critical behavior of the mixture is modified, with long-wavelength concentration fluctuations partially damped when the system is charged. It is also shown that the decrease of configurational entropy due to hyperuniformity originates from contributions beyond the two-particle level. Finally, despite global hyperuniformity, we show that in our system, the spatial configuration associated with each component separately is not hyperuniform, i.e., the system is not "multihyperuniform.

A sound card based multi-channel frequency measurement system

For physical processes which express themselves as a frequency, for example magnetic field measurements using optically-pumped alkali-vapor magnetometers, the precise extraction of the frequency from the noisy signal is a classical problem. We describe herein a frequency measurement system based on an inexpensive commercially available computer sound card coupled with a software single-tone estimator which reaches Cram\'er--Rao limited performance, a feature which commercial frequency counters often lack. Characterization of the system and examples of its successful application to magnetometry are presented.Comment: 4 pages, 3 figures, 1 tabl

Rb*He_n exciplexes in solid 4_He

We report the observation of emission spectra from Rb*He_n exciplexes in solid 4He. Two different excitation channels were experimentally identified, viz., exciplex formation via laser excitation to the atomic 5P3/2 and to the 5P1/2 levels. While the former channel was observed before in liquid helium, on helium nanodroplets and in helium gas by different groups, the latter creation mechanism occurs only in solid helium or in gaseous helium above 10 Kelvin. The experimental results are compared to theoretical predictions based on the extension of a model, used earlier by us for the description of Cs*He_n exciplexes. We also report the first observation of fluorescence from atomic rubidium in solid helium, and discuss striking differences between the spectroscopic feature of Rb-He and Cs-He systems.Comment: 8 pages, 8 figure