Cold atoms in space: community workshop summary and proposed road-map

We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies

Vibrational spectra of (BaF \u3c inf\u3e 2 ) \u3c inf\u3e n (n=1-6) clusters

© 2016 Author(s). The vibrational properties of alkaline-earth metal fluoride clusters (BaF2)n (n=1-6) are investigated in the framework of density functional theory. The calculated Raman and Infrared (IR) spectra reveals shift in Raman and IR peak position towards lower frequency region with the increase in the cluster size. Further the calculated spectra have been compared with the experimental vibrational spectra of bulk BaF2 crystal. Even though the smaller size cluster lacks translational symmetry, the structural and vibrational characteristic of (BaF2)5-6 are nearer to bulk counterpart

A theoretical study of structural and electronic properties of alkaline-earth fluoride clusters

The structural evolution and variation of electronic properties of alkaline-earth metal fluoride clusters (MF2)n (M=Mg, Ca, Sr, Ba; n=1-6) are investigated using density functional theory. All these clusters demonstrate ionic-bonding dominated through all sizes considered here, and generally show a preference of 3D structures when n≥4. It is found that the structural evolution of (MgF2)n clusters are distinct from the rest of the alkaline-earth clusters owing to the competitive interplay of much smaller ionic radius of Mg and the stronger Mg-F bond. In the ground state configurations, (MgF2)n clusters prefer the planar building units, whereas the rest of the (MF2)n clusters prefer the 3D building units of a M2F3 type maximizing the coordination number of the constituent metal atoms. The variations of the binding energy, the ionization potential, the electron affinity and the HOMO-LUMO gap with the cluster size are explained in terms of the change in the ionic radius and the basicity of the constituent metal ions in going from (MgF2)n to (CaF2)n, (SrF2)n, and (BaF2)n. © 2014 Elsevier B.V

Temperature dependent interaction of hydrogen with PdAg nanocomposite thin films revealed by in-situ synchrotron XRD

PdAg nanocomposite alloy thin films were synthesized using a DC magnetron sputtering process to study the structural changes that occur in the alloy film during the process of hydrogenation and dehydrogenation at different temperatures. The atomic composition of the nano-composite film is 88 at % Pd and 12% at Ag, as determined by the EDAX analysis. In-situ synchrotron X-ray diffraction (XRD) has been used to monitor the subtle structural changes that occurred throughout the hydrogenation and dehydrogenation cycles at an interval of 10 s. This aspect has not been addressed so far. In-situ XRD studies reveal that the XRD peak shifts towards a lower angle due to the lattice expansion in the alloy due to hydrogenation. The change in peak shift is found to be different for different temperatures. The present study also shows no hysteresis during the hydrogen absorption and desorption processes. In addition, the results show that (i) the phase segregation has been observed at 250 , (ii) the peak shift during the hydrogenation process at higher temperatures is not significant, whereas the peak shift throughout the process is more rapid and pronounced at ambient temperature

In-situ investigation on hydrogenation-dehydrogenation of Pd–Ag alloy films

The present work reports on synthesis of PdeAg nano-composite films by magnetron cosputteringand the structural changes in the alloy film during hydrogenation and dehydrogenation.Synchrotron X-ray diffraction is employed in-situ to reveal subtle structuralchanges occurring during hydrogenation and dehydrogenation processes, an aspect notinvestigated so far. It is revealed that the nanocomposite film having 88 at% Pd shows theformation of a-phase as an intermediate phase, however, completion of the hydrogenationprocess yields only b-phase. No b-phase formation is observed in nanocomposite thin filmcontaining 54 at% of Pd, suggesting the suppression of formation of b-phase with increasein Ag concentration. On dehydrogenation, the peak returns to its original position i.e. thevalue before hydrogenation. The data also demonstrated that the addition of Ag in Pd resultsin complete removal of dissolved hydrogen thereby eliminates the problem of hysteresis.The study shows that the lower concentrations of Ag in Pd are better in terms ofextent of peak-shift on hydrogenation/dehydrogenation and faster response/recoverykinetics