Measuring work and heat in ultracold quantum gases

We propose a feasible experimental scheme to direct measure heat and work in cold atomic setups. The method is based on a recent proposal which shows that work is a positive operator valued measure (POVM). In the present contribution, we demonstrate that the interaction between the atoms and the light polarisation of a probe laser allows us to implement such POVM. In this way the work done on or extracted from the atoms after a given process is encoded in the light quadrature that can be measured with a standard homodyne detection. The protocol allows one to verify fluctuation theorems and study properties of the non-unitary dynamics of a given thermodynamic process.Comment: Published version in the Focus Issue on "Quantum Thermodynamics

Optical photometry of the UCM Lists I and II

We present Johnson B CCD photometry for the whole sample of galaxies of the Universidad Complutense de Madrid (UCM) Survey Lists I and II. They constitute a well-defined and complete sample of galaxies in the Local Universe with active star formation. The data refer to 191 S0 to Irr galaxies at an averaged redshift of 0.027, and complement the already published Gunn r, J and K photometries. In this paper the observational and reduction features are discussed in detail, and the new colour information is combined to search for clues on the properties of the galaxies, mainly by comparing our sample with other surveys.Comment: 14 pages, 7 PostScript figures, accepted for publication in A&AS, also available vi ftp at ftp://cutrex.fis.ucm.es/pub/OUT/pag/PAPERS

Resonant demagnetization of a dipolar BEC in a 3D optical lattice

We study dipolar relaxation of a chromium BEC loaded into a 3D optical lattice. We observe dipolar relaxation resonances when the magnetic energy released during the inelastic collision matches an excitation towards higher energy bands. A spectroscopy of these resonances for two orientations of the magnetic field provides a 3D band spectroscopy of the lattice. The narrowest resonance is registered for the lowest excitation energy. Its line-shape is sensitive to the on-site interaction energy. We use such sensitivity to probe number squeezing in a Mott insulator, and we reveal the production of three-body states with entangled spin and orbital degrees of freedom.Comment: 5 pages, 3 Figures, Supplemental Materia

Noise models for superoperators in the chord representation

We study many-qubit generalizations of quantum noise channels that can be written as an incoherent sum of translations in phase space. Physical description in terms of the spectral properties of the superoperator and the action in phase space are provided. A very natural description of decoherence leading to a preferred basis is achieved with diffusion along a phase space line. The numerical advantages of using the chord representation are illustrated in the case of coarse-graining noise.Comment: 8 pages, 5 .ps figures (RevTeX4). Submitted to Phys. Rev. A. minor changes made, according to referee suggestion

Luminous Compact Blue Galaxies up to z~1 in the HST Ultra Deep Field: I. Small galaxies, or blue centers of massive disks?

We analyze 26 Luminous Compact Blue Galaxies (LCBGs) in the HST/ACS Ultra Deep Field (UDF) at z ~ 0.2-1.3, to determine whether these are truly small galaxies, or rather bright central starbursts within existing or forming large disk galaxies. Surface brightness profiles from UDF images reach fainter than rest-frame 26.5 B mag/arcsec^2 even for compact objects at z~1. Most LCBGs show a smaller, brighter component that is likely star-forming, and an extended, roughly exponential component with colors suggesting stellar ages >~ 100 Myr to few Gyr. Scale lengths of the extended components are mostly >~ 2 kpc, >1.5-2 times smaller than those of nearby large disk galaxies like the Milky Way. Larger, very low surface brightness disks can be excluded down to faint rest-frame surface brightnesses (>~ 26 B mag/arcsec^2). However, 1 or 2 of the LCBGs are large, disk-like galaxies that meet LCBG selection criteria due to a bright central nucleus, possibly a forming bulge. These results indicate that >~ 90% of high-z LCBGs are small galaxies that will evolve into small disk galaxies, and low mass spheroidal or irregular galaxies in the local Universe, assuming passive evolution and no significant disk growth. The data do not reveal signs of disk formation around small, HII-galaxy-like LCBGs, and do not suggest a simple inside-out growth scenario for larger LCBGs with a disk-like morphology. Irregular blue emission in distant LCBGs is relatively extended, suggesting that nebular emission lines from star-forming regions sample a major fraction of an LCBG's velocity field.Comment: 11 pages, 2 figures, AASTeX; accepted for publication in Astrophysical Journal Letter

Dipolar atomic spin ensembles in a double-well potential

We experimentally study the spin dynamics of mesoscopic ensembles of ultracold magnetic spin-3 atoms located in two separated wells of an optical dipole trap. We use a radio-frequency sweep to selectively flip the spin of the atoms in one of the wells, which produces two separated spin domains of opposite polarization. We observe that these engineered spin domains are metastable with respect to the long-range magnetic dipolar interactions between the two ensembles. The absence of inter-cloud dipolar spin-exchange processes reveals a classical behavior, in contrast to previous results with atoms loaded in an optical lattice. When we merge the two subsystems, we observe spin-exchange dynamics due to contact interactions which enable the first determination of the s-wave scattering length of 52Cr atoms in the S=0 molecular channel a_0=13.5^{+11}_{-10.5}a_B (where a_B is the Bohr radius).Comment: 9 pages, 7 figure