The vortex depinning transition in untwinned YBaCuO using complex impedance measurements

We present surface impedance measurement of the vortex linear response in a large untwinned YBCO crystal. The depinning spectra obtained over a broad frequency range (100 Hz- 30 MHz) are those of a surface pinned vortex lattice with a free flux flow resistivity (two modes response). The critical current in the "Campbell" like regime and the flux flow resistivity in the dissipative regime are extracted. Those two parameters are affected by the first order transition, showing that this transition may be related to the electronic state of vortices.Comment: to be published in the proceedings of M2S RI

Irreducible decompositions and stationary states of quantum channels

For a quantum channel (completely positive, trace-preserving map), we prove a generalization to the infinite dimensional case of a result by Baumgartner and Narnhofer. This result is, in a probabilistic language, a decomposition of a general quantum channel into its irreducible positive recurrent components. This decomposition is related with a communication relation on the reference Hilbert space. This allows us to describe the full structure of invariant states of a quantum channel, and of their supports

From n+1-level atom chains to n-dimensional noises

In quantum physics, the state space of a countable chain of (n+1)-level atoms becomes, in the continuous field limit, a Fock space with multiplicity n. In a more functional analytic language, the continuous tensor product space over R of copies of the space C^{n+1} is the symmetric Fock space Gamma_s(L^2(R;C^n)). In this article we focus on the probabilistic interpretations of these facts. We show that they correspond to the approximation of the n-dimensional normal martingales by means of obtuse random walks, that is, extremal random walks in R^n whose jumps take exactly n+1 different values. We show that these probabilistic approximations are carried by the convergence of the basic matrix basis a^i_j(p) of \otimes_N \CC^{n+1} to the usual creation, annihilation and gauge processes on the Fock space.Comment: 22 page

Galvanomagnetic properties and noise in a barely metallic film of V2O3

We have measured the magnetotransport properties of a strained metallic V2O3 thin film. Most of the properties are similar to V2O3 single crystals that have been submitted to a large pressure. In addition, resistance noise analysis indicates that conductivity fluctuations are freezing out at T\approx 10K. Examination of a range of measurements leads to the conclusion that spins-configuration fluctuations dominate in the low temperature regime.Comment: accepted for publication in Phys Rev