Abstracts Category : Other

Impurity dynamics and nearest-neighbor interactions in one-dimensional lattices

by Anne-Maria Visuri

An impurity coupled to a bath is a paradigmatic problem of many-body physics and relevant for various systems. In this work, we study the dynamics due to impurities in one-dimensional lattice systems using the numerical time-evolving block decimation method and analytic calculations. We consider both noninteracting and interacting fermions as the bath, in particular fermions in a singlet superfluid state due to attractive on-site interactions, and baths with a periodic or nearly periodic structure due to nearest-neighbor repulsion. Previous theoretical and experimental research mainly considers homogeneous baths with contact interactions.We find novel phenomena when the bath is probed with energies above its characteristic energyscale. In publication I, a driven perturbation with velocity above the speed of sound of the interacting fermions retains the ground-state power-law decay of singlet superfluid correlations. In publication III, we study the decoherence of an impurity in terms of the purity of its density matrix. The impurity and the bath fermions have different masses, and we find the fastest decoherence for a light impurity in a heavy bath, whereas the fastest dissipation of energy occurs for equal masses.In publications II and IV, we consider a bath of fermions with repulsive nearest-neighbor interactions. In a half-filled lattice, the bath is in the Mott insulator state with a particle every two sites. A filling above one half leads to solitons seen as domain walls in the arrangement of the particles. We find that within a resonance region of interactions, the impurity can create an additional soliton-antisoliton pair in the bath. These two excitations have very different dynamics: The antisoliton can form a bound state with the impurity while the soliton excitation propagates. When the ground state of the bath contains solitons, the antisoliton excitation is confined close to its origin. These phenomena are explained by energy conservation, since processes with an energy change larger than the bandwidth are suppressed.Recent developments in experiments with ultracold gases in optical lattices offer possibilities for testing the theoretical predictions of this work. Long-range interactions in lattice models have been observed in experiments with magnetic atoms and dipolar molecules. Furthermore, single-site addressing techniques allow to create localized impurities and track their motion, and to measure the purity of many-body states.; Hiukkaskylvyn kanssa vuorovaikuttavat eppuhtaushiukkaset esiintyvt usein monen kappaleen fysiikassa. Tss tyss eppuhtaushiukkasten teoriaa tutkitaan yksidimensioisissa hiloissa kytten sek numeerista time-evolving block decimation -menetelm (hajotelma kvanttimekaanisen aikakehityksen laskemiseen) ett analyyttisi menetelmi. Hilassa hiukkasten liike-energiaa rajoittaa energiavyn leveys. Lydmme uudenlaisia ajasta riippuvia ilmiit, kun hiukkaskylpy hiritn vynleveytt suuremmalla energia-alueella.Julkaisu I ksittelee singlettisupranestetilassaAdvisors/Committee Members: Trm, Pivi, Prof., Aalto University, Department of Applied Physics, Finland (advisor).