A Static or Dynamic Atom?

John B. Underwood

C. Y. Lee, J. M. Hettema, Thomas F. Gallagher +1 more

We report measurements of the microwave ionization of Rydberg atoms as a function of static electric field, for static fields from zero to the classical ionization limit. The microwave-ionization threshold field shows clear structure as a function of the static field, in some static field regimes actually increasing as the static field is increased. The dependence of the microwave field can be understood by considering the dynamics of the levels in a temporally varying field.

Arthur Holly Compton

Marcelo A. Romero, Fernando Flores, E. C. Goldberg

In this work we introduce a formalism that provides a good description of the correlated charge states of an atom interacting statically or dynamically with a metal surface, including realistic features of the atom-surface system. Our treatment of the Anderson impurity with an intrasite finite repulsion is based on the use of a projection operator technique and the application of the equation of motion method. The specific case of charge state configurations having zero, one, and two valence electrons of atoms with $s$-type valence orbital is discussed in this work. Static properties, such as the average occupation and the local density of states at the atom site and dynamical charge fractions in atom scattering processes, are compared with exact calculations and also with other existing approximations. Our treatment of the finite electronic repulsion at the atom site also reproduces satisfactorily the experimental behavior of the transmission phase shift of a dot measured by Aharonov-Bohm interferometry in both weak and strong coupling limits.

Fangzhao Alex An, Eric J. Meier, Bryce Gadway

Ultracold atoms in optical lattices offer a unique platform for investigating disorder-driven phenomena. While static disordered site potentials have been explored in a number of experiments, a more general, dynamical control over site-energy and off-diagonal tunnelling disorder has been lacking. The use of atomic quantum states as synthetic dimensions has introduced the spectroscopic, site-resolved control necessary to engineer more tailored realisations of disorder. Here, we present explorations of dynamical and tunneling disorder in an atomic system by controlling laser-driven dynamics of atomic population in a momentum-space lattice. By applying static tunnelling phase disorder to a one-dimensional lattice, we observe ballistic quantum spreading. When the applied disorder fluctuates on time scales comparable to intersite tunnelling, we instead observe diffusive atomic transport, signalling a crossover from quantum to classical expansion dynamics. We compare these observations to the case of static site-energy disorder, where we directly observe quantum localisation.Cold atom quantum simulation has had challenges in realising the tailored, dynamic types of disorder relevant to real materials. Here, the authors use synthetic momentum-space lattices to engineer spatially and dynamically controlled disorder to observe ballistic, diffusive, and arrested atomic transport.

James Gerald Crowther