T>0 properties of the infinitely repulsive Hubbard model for arbitrary number of holes

Based on representations of the symmetric group $S_N$, explicit and exact Schr\"odinger equation is derived for $U=\infty$ Hubbard model in any dimensions with arbitrary number of holes, which clearly shows that during the movement of holes the spin background of electrons plays an important role. Starting from it, at T=0 we have analyzed the behaviour of the system depending on the dimensionality and number of holes. Based on the presented formalism thermodynamic quantities have also been expressed using a loop summation technique in which the partition function is given in terms of characters of $S_N$. In case of the studied finite systems, the loop summation have been taken into account exactly up to the 14-th order in reciprocal temperature and the results were corrected in higher order based on Monte Carlo simulations. The obtained results suggest that the presented formalism increase the efficiency of the Monte Carlo simulations as well, because the spin part contribution of the background is automatically taken into account by the characters of $S_N$.Comment: 26 pages, 1 embedded ps figure; Phil. Mag. B (in press

0.75 atoms improve the clock signal of 10,000 atoms

Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology, in particular to measure time and to realize the second. In a classical interferometer, an ensemble of atoms is prepared in one of the two input states, whereas the second one is left empty. In this case, the vacuum noise restricts the precision of the interferometer to the standard quantum limit (SQL). Here, we propose and experimentally demonstrate a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. We create a squeezed vacuum state containing an average of 0.75 atoms to improve the clock sensitivity of 10,000 atoms by 2.05 dB. The SQL poses a significant limitation for today's microwave fountain clocks, which serve as the main time reference. We evaluate the major technical limitations and challenges for devising a next generation of fountain clocks based on atomic squeezed vacuum.Comment: 9 pages, 6 figure

Spectral Line Shapes in Plasmas

International audienceFor the first two Spectral Line Shapes in Plasma workshops, participants submitted in total over 1,500 line-shape calculations. The studies collected in this Special Issue explore only a part of this immense work. This book is a reprint of the special issue that appeared in the online open access journal Atoms (ISSN 2218-2004) in 2014 (available at: http://www.mdpi.com/journal/atoms/special_issues/SpectralLineShapes)

Atoms in boxes: from confined atoms to electron-atom scattering

We show that both confined atoms and electron-atom scattering can be described by a unified basis set method. The central idea behind this method is to place the atom inside a hard potential sphere, enforced by a standard Slater type basis set multiplied by a cutoff factor. For confined atoms, where the wall is placed close to the atomic nucleus, we show how the energy of the highest occupied atomic orbital and the static polarizability of helium and neon atoms evolve with the confinement radius. To our knowledge, these are the first confined atom polarizability calculations that include correlation, through the use of time-dependent density-functional theory. By placing the atom in a large spherical box, with a wall outside the electron density, we obtain scattering phase shifts using a recently developed method [M. van Faassen, A. Wasserman, E. Engel, F. Zhang, and K. Burke, Phys. Rev. Lett. {\bf 99}, 043005 (2007)]. We show that the basis set method gives identical results to previously obtained phase shifts for $e$-H and $e$-He${}^{+}$ scattering.Comment: 8 pages, 6 figures, submitted to Journal of Chemical Physic

Coupled dynamics of atoms and radiation pressure driven interferometers

We consider the motion of the end mirror of a cavity in whose standing wave mode pattern atoms are trapped. The atoms and the light field strongly couple to each other because the atoms form a distributed Bragg mirror with a reflectivity that can be fairly high. We analyze how the dipole potential in which the atoms move is modified due to this backaction of the atoms. We show that the position of the atoms can become bistable. These results are of a more general nature and can be applied to any situation where atoms are trapped in an optical lattice inside a cavity and where the backaction of the atoms on the light field cannot be neglected. We analyze the dynamics of the coupled system in the adiabatic limit where the light field adjusts to the position of the atoms and the light field instantaneously and where the atoms move much faster than the mirror. We calculate the side band spectrum of the light transmitted through the cavity and show that these spectra can be used to detect the coupled motion of the atoms and the mirror.Comment: 11 pages; 13 figures; two added references and other minor correction

Atoms of None of the Elements Ionize While Atoms of Inert Behavior Split by Photonic Current

As studied, atoms deal with the positive or negative charge by losing or gaining an electron. However, the gaseous and solid atoms can execute interstate electron dynamics. They can also deal with transition states. Solid atoms can elongate from the east-west poles at the ground surface level. Under suitable energy, solid atoms can expand, and gaseous atoms can contract. When the excessive field is intact, flowing inert gas atoms can split. The splitting inert gas atoms convert into electron streams. Those electron streams carrying the photons when impinging on the naturally-elongated solid atoms, further elongation of the atoms takes place. If not, elongated atoms at least deform. Gaseous atoms can squeeze by the suffering of their lattices. Such behaviors of the atoms validate that they cannot ionize. On splitting the flowing inert gas atoms, characteristics of the photons become apparent. Those photons that are not carried by the electron streams can enter the air medium directly. On traveling photons in the air medium, their energy dissipates in heat, and their force confines in the form of a field. On confinement of the field of traveling photons with the field of air-medium, a glow of light is appeared, which is better known in plasma. The splitting of inert gas atoms, the carrying of photons by the electron streams, and the lighting of traveling photons validate that an electric current is photonic. In various microscopes, the magnification of an image is based on the resolving power of photons. Photonic current is due to the propagation of the photons in the structure of the interstate electron gap. Some well-known principles are also discussed, validating that an electric current is a photonic current. Indeed, this study brings about profound changes in science