Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas

We discuss unusual aspects of symmetry that can happen due to entropic effects in the context of multi-scalar field theories at finite temperature. We present their consequences, in special, for the case of nonrelativistic models of hard core spheres. We show that for nonrelativistic models phenomena like inverse symmetry breaking and symmetry non-restoration cannot take place, but a reentrant phase at high temperatures is shown to be possible for some region of parameters. We then develop a model of interest in studies of Bose-Einstein condensation in dilute atomic gases and discuss about its phase transition patterns. In this application to a Bose-Einstein condensation model, however, no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O. Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One reference was update

The Elephant Quantum Walk

We explore the impact of long-range memory on the properties of a family of quantum walks in a one-dimensional lattice and discrete time, which can be understood as the quantum version of the classical "Elephant Random Walk" non-Markovian process. This Elephant Quantum Walk is robustly superballistic with the standard deviation showing a constant exponent, $\sigma \propto t^{3/ 2}$ , whatever the quantum coin operator, on which the diffusion coefficient is dependent. On the one hand, this result indicates that contrarily to the classical case, the degree of superdiffusivity in quantum non- Markovian processes of this kind is mainly ruled by the extension of memory rather than other microscopic parameters that explicitly define the process. On the other hand, these parameters reflect on the diffusion coefficient.Comment: 4 figures, any comments is welcome. Accepted in PR

Inverse Symmetry Breaking in Multi-Scalar Field Theories

We review how the phenomena of inverse symmetry breaking (and symmetry nonrestoration) may arise in the context of relativistic as well as nonrelativistic multi-scalar field theories. We discuss how the consideration of thermal effects on the couplings produce different transition patterns for both theories. For the relativistic case, these effects allow the appearance of inverse symmetry breaking (and symmetry nonrestoration) at arbitrarily large temperatures. On the other hand, the same phenomena are suppressed in the nonrelativistic case, which is relevant for condensed matter physics. In this case, symmetry nonrestoration does not happen while inverse symmetry is allowed only to be followed by symmetry restoration characterizing a reentrant phase. The aim of this paper is to give more insight concerning the, qualitatively correct, results obtained by using one loop perturbation theory in the evaluation of thermal masses and couplings.Comment: 7 pages, 3 figures, talk given at the workshop on Quantum Fields Under the Influence of External Conditions, QFEXT05, Barcelona, sep-200

Evidence for entanglement at high temperatures in an engineered molecular magnet

The molecular compound [Fe$_{2}$($\mu_{2}$-oxo)(C$_{3}$H$_{4}$N$_{2}$)$_{6}$(C$_{2}$O$_{4}$)$_{2}$] was designed and synthesized for the first time and its structure was determined using single-crystal X-ray diffraction. The magnetic susceptibility of this compound was measured from 2 to 300 K. The analysis of the susceptibility data using protocols developed for other spin singlet ground-state systems indicates that the quantum entanglement would remain at temperatures up to 732 K, significantly above the highest entanglement temperature reported to date. The large gap between the ground state and the first-excited state (282 K) suggests that the spin system may be somewhat immune to decohering mechanisms. Our measurements strongly suggest that molecular magnets are promising candidate platforms for quantum information processing

Experimental Determination of Thermal Entanglement in Spin Clusters using Magnetic Susceptibility Measurements

The present work reports an experimental observation of thermal entanglement in a clusterized spin chain formed in the compound Na$_2$Cu$_5$Si$_4$O$_{14}$. The presence of entanglement was investigated through two measured quantities, an Entanglement Witness and the Entanglement of Formation, both derived from the magnetic susceptibility. It was found that pairwise entanglement exists below $\sim 200$ K. Tripartite entanglement was also observed below $\sim 240$ K. A theoretical study of entanglement evolution as a function of applied field and temperature is also presented.Comment: Submited to Phys. Rev.

The Friedreich ataxia GAA repeat expansion mutation induces comparable epigenetic changes in human and transgenic mouse brain and heart tissues

Friedreich ataxia (FRDA) is caused by a homozygous GAA repeat expansion mutation within intron 1 of the FXN gene, leading to reduced expression of frataxin protein. Evidence suggests that the mutation may induce epigenetic changes and heterochromatin formation, thereby impeding gene transcription. In particular, studies using FRDA patient blood and lymphoblastoid cell lines have detected increased DNA methylation of specific CpG sites upstream of the GAA repeat and histone modifications in regions flanking the GAA repeat. In this report we show that such epigenetic changes are also present in FRDA patient brain, cerebellum and heart tissues, the primary affected systems of the disorder. Bisulfite sequence analysis of the FXN flanking GAA regions reveals a shift in the FRDA DNA methylation profile, with upstream CpG sites becoming consistently hypermethylated and downstream CpG sites becoming consistently hypomethylated. We also identify differential DNA methylation at three specific CpG sites within the FXN promoter and one CpG site within exon 1. Furthermore, we show by chromatin immunoprecipitation (ChIP) analysis that there is overall decreased histone H3K9 acetylation together with increased H3K9 methylation of FRDA brain tissue. Further studies of brain, cerebellum and heart tissues from our GAA repeat expansion-containing FRDA YAC transgenic mice reveal comparable epigenetic changes to those detected in FRDA patient tissue. We have thus developed a mouse model that will be a valuable resource for future therapeutic studies targeting epigenetic modifications of the FXN gene to increase frataxin expression