Finite size effects and equilibration in Bose-Hubbard chains with central well dephasing

We investigate Bose-Hubbard chains in a central depleted well configuration, with dephasing in the middle well. We look at equilibration of populations, pseudo-entropy, and entanglement measures. Using stochastic integration in the truncated Wigner representation, we find that the initial quantum states of the occupied wells has an influence on the subsequent dynamics, and that with more than three wells, the chains do not reach a full equilibrium, with edge effects becoming important, and the time to reach the steady state becoming longer. The evolutions with and without phase diffusion are qualitatively different. We find no convincing evidence of entanglement in the final states with phase diffusion. Although at least one accepted measure indicates the presence of mode entanglement, we are easily able to show that it can give ambiguous predictions.Comment: 20 pages, 12 figures, theor

Tripartite and bipartite entanglement in continuous-variable tripartite systems

We examine one asymmetric adnd two fully symmetric Gaussian continuous-variable systems in terms of their tripartite and bipartite entanglement properties. We treat pure states and are able to find analytic solutions using the undepleted pump approximation for the Hamiltonian models, and standard beamsplitter relations for a model that mixes the outputs of optical parametric oscillators. Our two symmetric systems exhibit perfect tripartite correlations, but only in the unphysical limit of infinite squeezing. For more realistic squeezing parameters, all three systems exhibit both tripartite and bipartite entanglement. We conclude that none of the outputs are completely analogous to either GHZ or W states, but there are parameter regions where they produce T states introduced by Adesso \etal The qualitative differences in the output states for different interaction parameters indicate that continuous-variable tripartite quantum information systems offer a versatility not found in bipartite systems.Comment: 18 pages, 6 figures. arXiv admin note: text overlap with arXiv:1510.0182

Improved quantum correlations in second harmonic generation with a squeezed pump

We investigate the effects of a squeezed pump on the quantum properties and conversion efficiency of the light produced in single-pass second harmonic generation. Using stochastic integration of the two-mode equations of motion in the positive-P representation, we find that larger violations of continuous-variable harmonic entanglement criteria are available for lesser effective interaction strengths than with a coherent pump. This enhancement of the quantum properties also applies to violations of the Reid-Drummond inequalities used to demonstrate a harmonic version of the Einstein-Podolsky-Rosen paradox. We find that the conversion efficiency is largely unchanged except for very low pump intensities and high levels of squeezing.Comment: 19 pages, 7 figure

The lost sunspot cycle: New support from Be10 measurements

It has been suggested that the deficit in the number of spots on the surface of the Sun between 1790 and 1830, known as the Dalton minimum, contained an extra cycle that was not identified in the original sunspot record by Wolf. Though this cycle would be shorter and weaker than the average solar cycle, it would shift the magnetic parity of the solar magnetic field of the earlier cycles. This extra cycle is sometimes referred to as the 'lost solar cycle' or 'cycle 4b'. Here we reanalyse Be10 measurements with annual resolution from the NGRIP ice core in Greenland in order to investigate if the hypothesis regarding a lost sunspot cycle is supported by these measurements. Specifically, we make use of the fact that the Galactic cosmic rays, responsible for forming Be10 in the Earth's atmosphere, are affected differently by the open solar magnetic field during even and odd solar cycles. This fact enables us to evaluate if the numbering of cycles earlier than cycle 5 is correct. For the evaluation, we use Bayesian analysis, which reveals that the lost sunspot cycle hypothesis is likely to be correct. We also discuss if this cycle 4b is a real cycle, or a phase catastrophe, and what implications this has for our understanding of stellar activity cycles in general.Comment: accepted for publication in A&

Building a Sample of Distant Clusters of Galaxies

Candidate clusters of galaxies drawn from the sample identified from the moderately deep I-band data of the ESO Imaging Survey (EIS), have been used for follow-up optical/infrared imaging and spectroscopic observations. The observations were conducted to assess the nature of these candidates over a large range of redshifts. Currently, 163 EIS candidates have (V-I) colors, 15 have (I-K) and 65 cluster fields have been observed spectroscopically. From a preliminary analysis of these data, we find that > 65% of the candidates studied show strong evidence of being real physical associations, over the redshift range 0.2<z<1.1. The evidence in some cases comes directly from spectroscopic measurements, in others indirectly from the detection of overdensities of objects with either the same color or the same photometric redshift, or from a combination of color and spectroscopic information. Preliminary results also suggest that the redshift derived from the matched-filter algorithm is a reasonable measure of the cluster's redshift, possibly overestimating it by Delta z ~0.1, at least for systems at z<0.7. Overdensities of red objects have been detected in over 100 candidates, 38 of which with estimated redshifts >0.6, and six candidates in the interval 0.45<z<0.81 have either been identified directly from measured redshifts or have been confirmed by the measurement of at least one redshift for galaxies located along a red-sequence typical of cluster early-type galaxies. Lastly, five candidates among those already observed in the infrared have (I-Ks) colors consistent with them being in the redshift interval 0.8<z<1.1. The sample of "confirmed" clusters, already the largest of its kind in the southern hemisphere, will be further enlarged by ongoing observations.Comment: To appear in "Large Scale Structure in the X-ray Universe", ed. M. Plionis and I. Georgantopoulos (Paris: Editions Frontieres), in pres