# Heidelberg 2015 – wissenschaftliches Programm

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# A: Fachverband Atomphysik

## A 18: Poster: Ultra-cold atoms, ions and BEC (with Q)

### A 18.9: Poster

### Dienstag, 24. März 2015, 17:00–19:00, C/Foyer

**Out-of-equilibrium dynamics of two interacting bosons** — •Tim Keller^{1}, Thomás Fogarty^{1,2}, and Giovanna Morigi^{1} — ^{1}Theoretische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany — ^{2}Quantum Systems Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan

Small systems of ultracold quantum gases are a leading candidate for studying interesting quantum phenomena in interacting many-body systems. To this end we study the out-of-equilibrium dynamics of two interacting bosons in a one-dimensional harmonic trap after a quench by a delta-shaped potential located in the centre of the trap. We make use of an approximate variational calculation called Lagrange-mesh method to solve the Schrödinger equation. We examine the dynamics by calculating the single particle density and calculate the correlations between the particles via the von Neumann entropy. We investigate the irreversibility of the quenched system by calculating the Loschmidt echo. This is related to the spectral function, with which one can discern distinct scattering states created by the quench and the emergence of the orthogonality catastrophe. We show that a thorough examination of the parameter space leads to the excitation of distinct separate or collective oscillations and also the creation of NOON states depending on the interaction and strength of the quench. We also show that the distribution of the Loschmidt echo over large time scales can be used to identify different distinct regimes, which are heavily dependent on the interaction strength between the atoms.