Scaling-up quantum heat engines efficiently via shortcuts to adiabaticity

The finite-time operation of a quantum heat engine that uses a single particle as a working medium generally increases the output power at the expense of inducing friction that lowers the cycle efficiency. We propose to scale up a quantum heat engine utilizing a many-particle working medium in combination with the use of shortcuts to adiabaticity to boost the nonadiabatic performance by eliminating quantum friction and reducing the cycle time. To this end, we first analyze the finite-time thermodynamics of a quantum Otto cycle implemented with a quantum fluid confined in a time-dependent harmonic trap. We show that nonadiabatic effects can be controlled and tailored to match the adiabatic performance using a variety of shortcuts to adiabaticity. As a result, the nonadiabatic dynamics of the scaled-up many-particle quantum heat engine exhibits no friction and the cycle can be run at maximum efficiency with a tunable output power. We demonstrate our results with a working medium consisting of particles with inverse-square pairwise interactions, that includes noninteracting and hard-core bosons as limiting cases.Comment: 15 pages, 3 figures; typo in Eq. (51) fixed. Feature paper in the Special Issue "Quantum Thermodynamics" edited by Prof. Dr. Ronnie Koslof

Atom laser dynamics in a tight-waveguide

We study the transient dynamics that arise during the formation of an atom laser beam in a tight waveguide. During the time evolution the density profile develops a series of wiggles which are related to the diffraction in time phenomenon. The apodization of matter waves, which relies on the use of smooth aperture functions, allows to suppress such oscillations in a time interval, after which there is a revival of the diffraction in time. The revival time scale is directly related to the inverse of the harmonic trap frequency for the atom reservoir.Comment: 6 pages, 5 figures, to be published in the Proceedings of the 395th WE-Heraeus Seminar on "Time Dependent Phenomena in Quantum Mechanics ", organized by T. Kramer and M. Kleber (Blaubeuren, Germany, September 2007

Stability of spinor Fermi gases in tight waveguides

The two and three-body correlation functions of the ground state of an optically trapped ultracold spin-1/2 Fermi gas (SFG) in a tight waveguide (1D regime) are calculated in the plane of even and odd-wave coupling constants, assuming a 1D attractive zero-range odd-wave interaction induced by a 3D p-wave Feshbach resonance, as well as the usual repulsive zero-range even-wave interaction stemming from 3D s-wave scattering. The calculations are based on the exact mapping from the SFG to a ``Lieb-Liniger-Heisenberg'' model with delta-function repulsions depending on isotropic Heisenberg spin-spin interactions, and indicate that the SFG should be stable against three-body recombination in a large region of the coupling constant plane encompassing parts of both the ferromagnetic and antiferromagnetic phases. However, the limiting case of the fermionic Tonks-Girardeau gas (FTG), a spin-aligned 1D Fermi gas with infinitely attractive p-wave interactions, is unstable in this sense. Effects due to the dipolar interaction and a Zeeman term due to a resonance-generating magnetic field do not lead to shrinkage of the region of stability of the SFG.Comment: 5 pages, 6 figure

Respuestas vegetativa, productiva y calidad del aceite a la aplicación foliar de P y K a olivos “Arbequinos” y “Picual”

A completed hedgerow of cv. Arbequina and a youth vase trained orchard of cv. Picual were fertilized with foliar applications of Phosphorus (P) or Potassium (K) throughout four seasons. The orchards were located near Valdepeñas in the dry area of La Mancha (Spain). Vegetative growth, yield and oil quality were evaluated. Foliar treatments did not increase P or K leaf concentration. Most of the evaluated parameters were not significantly affected by treatments. It was observed that the P treatment increased olive growth and oil yield in both orchards and in certain seasons due to an increment in fruit number. P and K application significantly increased ‘Arbequina’ olive and oil yield in 2008 when spring was wetter than the other years. Oil quality was not modified by fertilizer treatments in the ‘Arbequina’orchard. However, oxidative stability was negatively affected by P and K treatments in ‘Picual’. Oil extraction could be negatively affected by treatments because of the increase in the water content in the fruit obtained from both orchards.Un olivar en seto completamente formado de la variedad Arbequina y otro olivar en vaso joven de la variedad Picual fueron tratados vía foliar con Fósforo (P) y Potasio (K) durante cuatro años. Los olivares estuvieron localizados cerca de Valdepeñas, en la zona árida de La Mancha (España). Se evaluaron el crecimiento vegetativo, el rendimiento y la calidad del aceite. Los tratamientos foliares no aumentaron los niveles foliares de P y K. La mayoría de parámetros de crecimiento y producción evaluados no se vieron afectados por los tratamientos. En ambos olivares y en algún año del ensayo, el tratamiento con P incrementó el crecimiento y el rendimiento, debido al incremento en el número de frutos. Las aplicaciones de P y K aumentaron significativamente el rendimiento en aceituna y aceite en Arbequina en 2008, cuando la primavera fue más húmeda que el resto de años. Los tratamientos no modificaron la calidad del aceite obtenido en ‘Arbequina’. Sin embargo, en ‘Picual’ los tratamientos con P y K afectaron negativamente a la estabilidad oxidativa del aceite. La extracción del aceite podría verse perjudicada por los tratamientos, debido al incremento en el contenido de agua en el fruto obtenido en ambos olivares

Dynamics of a Tonks-Girardeau gas released from a hard-wall trap

We study the expansion dynamics of a Tonks-Girardeau gas released from a hard wall trap. Using the Fermi-Bose map, the density profile is found analytically and shown to differ from that one of a classical gas in the microcanonical ensemble even at macroscopic level, for any observation time larger than a critical time. The relevant time scale arises as a consequence of fermionization.Comment: 4 pages, 6 figure

Tachyon warm inflationary universe model in the weak dissipative regime

Warm inflationary universe model in a tachyon field theory is studied in the weak dissipative regime. We develop our model for an exponential potential and the dissipation parameter $\Gamma=\Gamma_0$=constant. We describe scalar and tensor perturbations for this scenario.Comment: 9 pages, accepted by European Physical Journal