Replica Symmetry Breaking in Cold Atoms and Spin Glasses

We consider a system composed by N atoms trapped within a multimode cavity, whose theoretical description is captured by a disordered multimode Dicke model. We show that in the resonant, zero field limit the system exactly realizes the Sherrington-Kirkpatrick model. Upon a redefinition of the temperature, the same dynamics is realized in the dispersive, strong field limit. This regime also gives access to spin-glass observables which can be used to detect Replica Symmetry Breaking.Comment: 6 pages, 3 figure

Nonlocal compensation of pure phase objects with entangled photons

We suggest and demonstrate a scheme for coherent nonlocal compensation of pure phase objects based on two-photon polarization and momentum entangled states. The insertion of a single phase object on one of the beams reduces the purity of the state and the amount of shared entanglement, whereas the original entanglement can be retrieved by adding a suitable phase object on the other beam. In our setup polarization and momentum entangled states are generated by spontaneous parametric downconversion and then purified using a programmable spatial light modulator, which may be also used to impose arbitrary space dependent phase functions to the beams. As a possible application, we suggest and demonstrate a quantum key distribution protocol based on nonlocal phase compensation.Comment: 7 pages, 5 figure

AFM study of oxygen reduction products on HOPG in the LiPF6–DMSO electrolyte

Ex situ atomic force microscopy (AFM) has been used to study the morphology of oxygen reduction products in the LiPF6–dimethyl sulfoxide (DMSO) electrolyte, i.e. Li2O2 on a highly oriented pyrolytic graphite (HOPG) surface. Both cyclic voltammetry and chronoamperometry have shown that at low cathodic polarization the initial deposits decorate the edge steps of HOPG. At higher overpotentials a massive deposit covers the terraces. Upon charging the battery cathode Li2O2 oxidation and dissolution do not take place until high overpotentials are reached at which solvent decomposition has been demonstrated by in situ FTIR studies.Fil: Herrera, Santiago Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Tesio, Alvaro Yamil. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Clarenc, Romain. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Calvo, Ernesto Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin

Programmable entanglement oscillations in a non Markovian channel

We suggest and demonstrate an all-optical experimental setup to observe and engineer entanglement oscillations of a pair of polarization qubits in a non-Markovian channel. We generate entangled photon pairs by spontaneous parametric downconversion (SPDC), and then insert a programmable spatial light modulator in order to impose a polarization dependent phase-shift on the spatial domain of the SPDC output and to create an effective non-Markovian environment. Modulation of the enviroment spectrum is obtained by inserting a spatial grating on the signal arm. In our experiment, programmable oscillations of entanglement are achieved, with the maximally revived state that violates Bell's inequality by 17 standard deviations.Comment: 4 pages, 4 figure

Optomechanical self-structuring in cold atomic gases

The rapidly developing field of optomechanics aims at the combined control of optical and mechanical (solid-state or atomic) modes. In particular, laser cooled atoms have been used to exploit optomechanical coupling for self-organization in a variety of schemes where the accessible length scales are constrained by a combination of pump modes and those associated to a second imposed axis, typically a cavity axis. Here, we consider a system with many spatial degrees of freedom around a single distinguished axis, in which two symmetries - rotations and translations in the plane orthogonal to the pump axis - are spontaneously broken. We observe the simultaneous spatial structuring of the density of a cold atomic cloud and an optical pump beam. The resulting patterns have hexagonal symmetry. The experiment demonstrates the manipulation of matter by opto-mechanical self-assembly with adjustable length scales and can be potentially extended to quantum degenerate gases.Comment: 20 pages, 6 figure

Management of red rice (Oryza sativa) and barnyardgrass (Echinochloa crus-galli) grown with sorghum with reduced rate of atrazine and mechanical methods.

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Quantum threshold for optomechanical self-structuring in a Bose-Einstein condensate

Theoretical analysis of the optomechanics of degenerate bosonic atoms with a single feedback mirror shows that self-structuring occurs only above an input threshold that is quantum mechanical in origin. This threshold also implies a lower limit to the size (period) of patterns that can be produced in a condensate for a given pump intensity. These thresholds are interpreted as due to the quantum rigidity of Bose-Einstein condensates, which has no classical counterpart. Above the threshold, the condensate self-organizes into an ordered supersolid state with a spatial period self-selected by optical diffraction

A critique of Rasch analysis using the Dyspnoea‐12 as an illustrative example

Aim. This paper is a report of a study of the application and critique of Rasch analysis to the development of the Dyspnoea‐12 questionnaire; an instrument that measures breathlessness severity. Background. The development of questionnaires has traditionally involved application of classical test theory. Rasch analysis has gained international momentum as a robust application of ‘modern’ psychometric testing for the development of new instruments and the refinement of existing ones. Method. A total of 358 patients [mean age 62 (sd = 8); chronic obstructive pulmonary disease = 123, interstitial lung disease = 129, heart failure = 106], responded to an initial list of 81 items (between May 2006 and February 2008). Hierarchical modelling reduced the list to 34 items. Rasch analysis was used to inform decisions about further item removal and fit to the unidimensional model. Rasch analysis included tests of item response appropriateness, item residual, differential item functioning (including gender and diagnosis) and unidimensionality. Results. Twenty‐two items failed to reach the requirements of the Rasch model and were removed. Reasons included high residuals and item bias associated with gender and diagnosis. The 12‐items conformed to the Rasch unidimensional parameters (number of statistically significant t‐tests 6·7%; confidence interval: 4·4–9·0%). Conclusion. We have presented the steps involved in reducing and refining a large item‐set by identifying those items which possessed the most reliable measurement properties. The Dyspnoea‐12 is reliable and simple to use and should find utility in both practice and research settings. We recommend that nurses consider Rasch analysis in the development of health‐related questionnaires