Work, heat and entropy production in bipartite quantum systems

In bipartite quantum systems commutation relations between the Hamiltonian of each subsystem and the interaction impose fundamental constraints on the dynamics of each partition. Here we investigate work, heat and entropy production in bipartite systems characterized by particular commutators between their local Hamiltonians and the interaction operator. We consider the formalism of [Weimer, EPL, 83:30008, 2008], in which heat (work) is identified with energy changes that (do not) alter the local von Neumann entropy, as observed in an effective local measurement basis. We demonstrate the consequences of the commutation relations on the work and heat fluxes into each partition, and extend the formalism to open quantum systems where one, or both, partitions are subject to a Markovian thermal bath. We also discuss the relation between heat and entropy in bipartite quantum systems out of thermal equilibrium, and reconcile the aforementioned approach with the second law of thermodynamics.Comment: 16 pages, 2 figures (to appear in NJP

Restrictions on the coherence of the ultrafast optical emission from an electron-hole pairs condensate

We report on the transfer of coherence from a quantum-well electron-hole condensate to the light it emits. As a function of density, the coherence of the electron-hole pair system evolves from being full for the low density Bose-Einstein condensate to a chaotic behavior for a high density BCS-like state. This degree of coherence is transfered to the light emitted in a damped oscillatory way in the ultrafast regime. Additionally, the photon field exhibits squeezing properties during the transfer time. We analyze the effect of light frequency and separation between electron and hole layers on the optical coherence. Our results suggest new type of ultrafast experiments for detecting electron-hole pair condensation.Comment: 4 pages,3 figures, to be published in Physical Review Letters. Minor change

Microestructura y resistencia a la corrosión de nitruros de cromo obtenidos por nitruración gaseosa al vacío de cromo electrolítico depositado sobre acero AISI H13.

En este artículo se caracteriza la microestructura y se evalúa la resistencia a la corrosión de nitruros de cromo obtenidos a partir de un tratamiento dúplex constituido por un recubrimiento electrolítico de cromo aplicado sobre un acero AISIH13 combinado posteriormente a un proceso de nitruración gaseosa, mediante un tratamiento termoquímico al vacío, utilizando NH3 como gas precursor de nitrógeno. Este tipo de tratamientos dúplex permite combinar las ventajas de tratamientos individuales y con este efecto sinérgico, obtener compuestos tipo CrxN en forma más económica que los producidos tradicionalmente de deposición física en fase de vapor (PVD). Los resultados obtenidos mediante difracción de rayos-X (XRD) indican una transformación superficial y subsuperficial del recubrimiento electrolítico de cromo con formación de fases CrN y Cr2N. Así mismo, los ensayos de polarización potenciodinámica indican un incremento en la resistencia a la corrosión de este tipo de compuestos en comparación con los obtenidos con cromo duro electrolítico.

Maximally entangled mixed states of two atoms trapped inside an optical cavity

In some off-resonant cases, the reduced density matrix of two atoms symmetrically coupled with an optical cavity can very approximately approach to maximally entangled mixed states or maximal Bell violation mixed states in their evolution. The influence of phase decoherence on the generation of maximally entangled mixed state is also discussed. PACS numbers: 03.67.-a, 03.65.UdComment: 7 pages, 4 figures, Latex, have a major revision of content

Métodos de enriquecimiento de glicoproteínas bacterianas para su posterior análisis y caracterización mediante espectrometría de masas

Comunicaciones a congreso

Entanglement of a microcanonical ensemble

We replace time-averaged entanglement by ensemble-averaged entanglement and derive a simple expression for the latter. We show how to calculate the ensemble average for a two-spin system and for the Jaynes-Cummings model. In both cases the time-dependent entanglement is known as well so that one can verify that the time average coincides with the ensemble average.Comment: 10 page

Diversity of the nitrite reductase gene nirS in the sediment of a free-water surface constructed wetland

The diversity of the nitrite reductase gene nirS was studied in the bulk sediment of a free-water surface constructed wetland (FWS-CW) located next to the Empuriabrava wastewater treatment plant (WWTP), in Castelló d’Empúries (Girona, NE Spain). The study period extended from the inception of the treatment wetland, in June 1998, until March 1999 and comprised periods of relatively high nitrate and ammonium concentrations at the influent and low nitrate-removal efficiencies. To evaluate nirS diversity, partial gene sequences were obtained by cloning of the respective PCR products. Rarefaction curves based on DOTUR analyses of the deduced amino-acid sequences predicted a greater diversity of nirS genes in samples containing higher ammonium concentrations. Estimated Shannon-Weaver indices of the four cloned samples showed a positive relationship with the N-NH4 +/N-NO3− ratios measured at the FWS-CW inlet. Identities between the deduced amino-acid sequences and those previously deposited in public databases ranged from 72 to 97%. Phylogenetic analysis based on these deduced sequences grouped 165 nirS clones in seven main clusters according to high similarity indices. Up to 60% of the clones clustered together in a highly homogeneous group with little homologies to any sequence retrieved from cultured representatives. Moreover, prevailing environmental conditions appeared to select for particular denitrifying populations, e.g., with respect to ammonium load and nitrogen removal efficiencies. This observation is of particular interest for the management of treatment wetlands, in which only slight variations in the theoretical denitrification potential of the system can occur. [Int Microbiol 2007; 10(4): 253-260

Ensemble averaged entanglement of two-particle states in Fock space

Recent results, extending the Schmidt decomposition theorem to wavefunctions of identical particles, are reviewed. They are used to give a definition of reduced density operators in the case of two identical particles. Next, a method is discussed to calculate time averaged entanglement. It is applied to a pair of identical electrons in an otherwise empty band of the Hubbard model, and to a pair of bosons in the the Bose-Hubbard model with infinite range hopping. The effect of degeneracy of the spectrum of the Hamiltonian on the average entanglement is emphasised.Comment: 19 pages Latex, changed title, references added in the conclusion