Current and entanglement in a Bose-Hubbard lattice

We study the generation of entanglement for interacting cold atoms in an optical lattice. The entanglement is generated by managing the interaction between two distinct atomic species. It is found that the current of one of the species can be used as a good indicator of entanglement generation. The thermalization process between the species is also shown to be closely related to the evolution of the current.Comment: 10 pages, 5 figure

Area Littlewood-Paley functions associated with Hermite and Laguerre operators

In this paper we study Lp-boundedness properties for area Littlewood-Paley functions associated with heat semigroups for Hermite and Laguerre operator

Aztec Economic Woes Continue

Initial estimates for the first quarter of 2009 indicate that the Mexican economy declined by 8.2 percent from the same period in 2008. The leading economic indicator index of INEGI, the national statistics institute, points to additional economic contraction in the coming months. The Consensus Mexico survey results are in agreement with the INEGI barometer. Panelist projections for real gross domestic product point to a comparatively steep decline. The current consensus forecast calls for a real GDP decrease for Mexico of -4.8 percent for the year as a whole.Mexico Economic Outlook

The Trough Deepens

As the third quarter of 2009 comes to a close, the Mexican economy remains severely battered. The latest INEGI data indicate that the second quarter of 2009 brought with it an annual GDP decrease, in real terms, of nearly 10.3 percent. The current consensus outlook calls for the light at the end of the tunnel to appear in 2010. In spite of this austere outlook, the financial system in Mexico has fared better than it did in prior recessions and the economy seems poised for growth once exports recover. The consensus outlook for real gross domestic product (GDP) calls for a noticeably sharp decline in 2009 of 7.1 percent. Relative to the consensus from last quarter, that represents a sharp downward revision. Individual panelist forecasts range from a drop of 6.5 percent to a steeper decline of 8.2 percent. An important source of the more pessimistic outlook is private consumption. Compared with the previous quarter, Mexican consumers are expected to reduce purchases by 6.9 percent, more than double the rate of decline expected three months ago.Mexico, Macroeconomic Forecast, Consensus Survey

Light at the End of Tunnel?

For 2009 as a whole, this quarter’s consensus outlook anticipates a steep decline of 6.9 percent in real gross domestic product (GDP). This outlook for inflation-adjusted GDP is not surprising given the panelists expectations for private consumption, as consumers are expected to reduce expenditures by 6.5 percent this year alone. Projections for the government stimulus package have declined substantially, however, with government consumption growth expected to slow to less than 1 percent. Diminished confidence in the Mexican business sector is still expected to cause total fixed investment to shrink at double digit rates. Given the lingering effects of the global economic downturn, the panelists also expect imports and exports to display steep contractions in excess of 11 and 22 percent, respectively. The 2009 consensus figure calls for consumer price increase in excess of 4 percent. Against this backdrop, the panelists expect a 2009 average exchange rate of 13.42 pesos per dollar. The consensus outlook for the 2009 yield on 28-day Treasury Certificates (CETES) holds steady at 5.5 percent, again, this quarter.Mexico, Macroeconomic Outlook, Consensus Survey

Optimization of soliton ratchets in inhomogeneous sine-Gordon systems

Unidirectional motion of solitons can take place, although the applied force has zero average in time, when the spatial symmetry is broken by introducing a potential $V(x)$, which consists of periodically repeated cells with each cell containing an asymmetric array of strongly localized inhomogeneities at positions $x_{i}$. A collective coordinate approach shows that the positions, heights and widths of the inhomogeneities (in that order) are the crucial parameters so as to obtain an optimal effective potential $U_{opt}$ that yields a maximal average soliton velocity. $U_{opt}$ essentially exhibits two features: double peaks consisting of a positive and a negative peak, and long flat regions between the double peaks. Such a potential can be obtained by choosing inhomogeneities with opposite signs (e.g., microresistors and microshorts in the case of long Josephson junctions) that are positioned close to each other, while the distance between each peak pair is rather large. These results of the collective variables theory are confirmed by full simulations for the inhomogeneous sine-Gordon system

First clear evidence of quantum chaos in the bound states of an atomic nucleus

We study the spectral fluctuations of the $^{208}$Pb nucleus using the complete experimental spectrum of 151 states up to excitation energies of $6.20$ MeV recently identified at the Maier-Leibnitz-Laboratorium at Garching, Germany. For natural parity states the results are very close to the predictions of Random Matrix Theory (RMT) for the nearest-neighbor spacing distribution. A quantitative estimate of the agreement is given by the Brody parameter $\omega$, which takes the value $\omega=0$ for regular systems and $\omega \simeq 1$ for chaotic systems. We obtain $\omega=0.85 \pm 0.02$ which is, to our knowledge, the closest value to chaos ever observed in experimental bound states of nuclei. By contrast, the results for unnatural parity states are far from RMT behavior. We interpret these results as a consequence of the strength of the residual interaction in $^{208}$Pb, which, according to experimental data, is much stronger for natural than for unnatural parity states. In addition our results show that chaotic and non-chaotic nuclear states coexist in the same energy region of the spectrum.Comment: 9 pages, 1 figur

Inhomogeneous soliton ratchets under two ac forces

We extend our previous work on soliton ratchet devices [L. Morales-Molina et al., Eur. Phys. J. B 37, 79 (2004)] to consider the joint effect of two ac forces including non-harmonic drivings, as proposed for particle ratchets by Savele'v et al. [Europhys. Lett. 67}, 179 (2004); Phys. Rev. E {\bf 70} 066109 (2004)]. Current reversals due to the interplay between the phases, frequencies and amplitudes of the harmonics are obtained. An analysis of the effect of the damping coefficient on the dynamics is presented. We show that solitons give rise to non-trivial differences in the phenomenology reported for particle systems that arise from their extended character. A comparison with soliton ratchets in homogeneous systems with biharmonic forces is also presented. This ratchet device may be an ideal candidate for Josephson junction ratchets with intrinsic large damping

Ratchet behavior in nonlinear Klein-Gordon systems with point-like inhomogeneities

We investigate the ratchet dynamics of nonlinear Klein-Gordon kinks in a periodic, asymmetric lattice of point-like inhomogeneities. We explain the underlying rectification mechanism within a collective coordinate framework, which shows that such system behaves as a rocking ratchet for point particles. Careful attention is given to the kink width dynamics and its role in the transport. We also analyze the robustness of our kink rocking ratchet in the presence of noise. We show that the noise activates unidirectional motion in a parameter range where such motion is not observed in the noiseless case. This is subsequently corroborated by the collective variable theory. An explanation for this new phenomenom is given