QUROPE Quantum Information Processing and Communication in Europe

Time-periodic driving like lattice shaking offers a low-demanding method to generate artificial gauge fields in optical lattices. We identify the relevant symmetries that have to be broken by the driving function for that purpose and demonstrate the power of this method by making concrete proposals for its application to two-dimensional lattice systems: We show how to tune frustration and how to create and control band touching points like Dirac cones in the shaken kagome lattice.

We discuss a general framework for the realization of a family of abelian lattice gauge theories, i.e., link models or gauge magnets, in optical lattices. We analyze the properties of these models that make them suitable to quantum simulations. Within this class, we study in detail the phases of a U(1)-invariant lattice gauge theory in 2+1 dimensions originally proposed by Orland. By using exact diagonalization, we extract the low-energy states for small lattices, up to 4x4.

We study strongly correlated phases of a pseudo-spin-1/2 Bose gas in an artificial gauge field using the exact diagonalization method. The atoms are confined in two dimensions and interact via a two-body contact potential. In Abelian gauge fields, pseudospin singlets are favored by pseudo-spin-independent interactions. We find a series of incompressible phases at fillings ν=2k/3.

We solve the open question of the existence of four-qubit entangled symmetric states with positive partial transpositions (PPT states). We reach this goal with two different approaches. First, we propose a half-analytical–half-numerical method that allows us to construct multipartite PPT entangled symmetric states (PPTESSs) from the qubit-qudit PPT entangled states. Second, we adapt the algorithm allowing us to search for extremal elements in the convex set of bipartite PPT states [ Phys. Rev.

We study a system of polar dipolar fermions in a two-dimensional optical lattice and show that multi-band Fermi-Hubbard model is necessary to discuss such system. By taking into account both on-site, and long-range interactions between different bands, as well as occupation-dependent inter- and intra-band tunneling, we predict appearance of novel phases in the strongly-interacting limit.

We study a system of polar fermions in a two-dimensional optical lattice and show that the multiband Fermi-Hubbard model is necessary to discuss its properties. We take into account both onsite and long-range interactions between different bands, as well as occupation-dependent inter- and intraband tunnelings. For strong-enough dipolar interactions we predict the appearances of phases such as multiband crystals, smectic metal, and exotic p-wave supersolids.

We investigate the relation between unextendible product bases (UPB) and Bell inequalities found recently in R. Augusiak et al. [ Phys. Rev. Lett. 107 070401 (2011)]. We, first, review the procedure introduced there that associates to any set of mutually orthogonal product vectors in a many-qubit Hilbert space a Bell inequality.

We use the exact diagonalization method to analyze the possibility of generating strongly correlated states in two-dimensional clouds of ultracold bosonic atoms that are subjected to a geometric gauge field that was created by coupling two internal atomic states to a laser beam. On tuning the gauge field strength, the system undergoes stepwise transitions between different ground states (GSs), which we describe by using analytical trial wave functions, including the Pfaffian (Pf), the Laughlin and a Laughlin quasiparticle many-body state.

Dieter Meschede (P6 UBONN) talk "Digital Control of Neutral Atoms"

Andrea Alberti (P6 UBONN) talk "Interferometers, quantum walks, and Bloch oscillations"