Synthetic clock transitions via continuous dynamical decoupling

Decoherence of quantum systems due to uncontrolled fluctuations of the environment presents fundamental obstacles in quantum science. `Clock' transitions which are insensitive to such fluctuations are used to improve coherence, however, they are not present in all systems or for arbitrary system parameters. Here, we create a trio of synthetic clock transitions using continuous dynamical decoupling in a spin-1 Bose-Einstein condensate in which we observe a reduction of sensitivity to magnetic field noise of up to four orders of magnitude; this work complements the parallel work by Anderson et al. (submitted, 2017). In addition, using a concatenated scheme, we demonstrate suppression of sensitivity to fluctuations in our control fields. These field-insensitive states represent an ideal foundation for the next generation of cold atom experiments focused on fragile many-body phases relevant to quantum magnetism, artificial gauge fields, and topological matter.Comment: 8 pages, 4 figures, Supplemental material

Perpetual emulation threshold of PT-symmetric Hamiltonians

We describe a technique to emulate a two-level \PT-symmetric spin Hamiltonian, replete with gain and loss, using only the unitary dynamics of a larger quantum system. This we achieve by embedding the two-level system in question in a subspace of a four-level Hamiltonian. Using an \textit{amplitude recycling} scheme that couples the levels exterior to the \PT-symmetric subspace, we show that it is possible to emulate the desired behaviour of the \PT-symmetric Hamiltonian without depleting the exterior, reservoir levels. We are thus able to extend the emulation time indefinitely, despite the non-unitary \PT dynamics. We propose a realistic experimental implementation using dynamically decoupled magnetic sublevels of ultracold atoms.Comment: 15 pages, 8 figure

Fourier transform spectroscopy of a spin-orbit coupled Bose gas

We describe a Fourier transform spectroscopy technique for directly measuring band structures, and apply it to a spin-1 spin-orbit coupled Bose-Einstein condensate. In our technique, we suddenly change the Hamiltonian of the system by adding a spin-orbit coupling interaction and measure populations in different spin states during the subsequent unitary evolution. We then reconstruct the spin and momentum resolved spectrum from the peak frequencies of the Fourier transformed populations. In addition, by periodically modulating the Hamiltonian, we tune the spin-orbit coupling strength and use our spectroscopy technique to probe the resulting dispersion relation. The frequency resolution of our method is limited only by the coherent evolution timescale of the Hamiltonian and can otherwise be applied to any system, for example, to measure the band structure of atoms in optical lattice potentials

The mean frequency of recurrence of in-time-multidimensional events for drought analyses

International audienceDroughts are related with prolonged periods when moisture is significantly below normal values. Drought indices attempt to scale the main drought features to facilitate comparisons. Numerous indices are found in the literature based on different drought features. Many of them were created for particular places and specific objectives, and therefore not suitable to generalize the results. However, there have been attempts to develop a general index, which would provide full characterization of drought events. Two of the most well known are the Palmer Drought Severity Index (PDSI) and the Standard Precipitation Index (SPI). Each one has particular advantages and disadvantages. Still neither of them or any other includes a full representation of droughts in a single value index, being useful for all general application. The fact that droughts have a random nature prescribes the statistical theory for the foundation of a complete and generic index, which would meet this goal. In this work, a procedure that allows a complete statistical characterization of drought events is presented. Droughts are characterized, from a statistical point of view, based both on the deviation from a normal regime and persistence. The events are represented as multivariate ones, whose dimensionality depends on the duration. Equal duration events are discriminated through their deviations from normality. The mean frequency of recurrence (MFR) is theoretically derived for such multivariate events, and it is used to scale such deviations. Therefore, events with different dimensionalities can be compared on a common dimension of interest, the MFR. This may be used as a drought index for drought characterization, both for analyzing historical events and monitoring current conditions. It may also be applied to analyze precipitation, streamflows and other hydroclimatic records. Its statistical nature and its general conception support its universality. Results may be applied not only to drought analysis, but also to analyze other random natural hazards. Applications of the procedure for drought analysis in Texas (USA) and in Gibraltar (Iberian Peninsula) are made and compared with PDSI and SPI results. The MFR applied over drought analysis allows the representation of the main drought characteristics in a single value, based on the statistical feature of the phenomenon, and scaled on the mean frequency of recurrence

Contribución a la palinología de Liliaceae en Andalucía Occidental (excepto subfamilias Scilloideae y Allioideae)

Se estudia la morfol ogía del polen de 23 especies de Liliaceae en Andal ucía Occidental, pertenecientes a los géneros Asphodelus, Anthericum, Simethis, Aphyllanthes, Colchicum, Merendera, Gag ea , Tulipa, Fri tillaría, Po!ygonatum, Asparagus, Ruscus y Smilax. Por l os caracteres polinices analizados se reconocen 14 tipos diferentes . Palinológicamente está justificada la separación de Smilacoideae como familia independiente , pero no se justifica la separación de Liliaceae y AmaryllidaceaeThe pollen morphol ogy of 23 species of Liliaceae from W. Andalucía belonging to the genera Asphodelus, Anthericum, Simethis, Aphyllanthes, Colchicum , Merendera, Gagea, Tulipa , Fritillaria, Polygonatum, Asparagus, Ruscus and Smilax have been studied. Fourteen types of pollen grains have been found, which are more or l ess in accordance wi t h the accepted genera . The palynol ogical data agree wi th the separation o f Smila9oideae as a different family. The tradi ti anal separation of Liliaceae a nd Amaryllidaceae is not justificd palynologicall