QUROPE Quantum Information Processing and Communication in Europe

The official web domain for the QUTE-EUROPE project has been registered under http://qute-europe.eu/.

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.

The counting statistics give insight into the properties of quantum states of light and other quantum states of matter such as ultracold atoms or electrons. The theoretical description of photon counting was derived in the 1960s and was extended to massive particles more recently. Typically, the interaction between each particle and the detector is assumed to be limited to short time intervals, and the probability of counting particles in one interval is independent of the measurements in previous intervals.

Dieter Meschede (P6 UBONN) talk "Bottom up to Discrete Quantum Simulation with Neutral Atoms"

We apply the Collins-Huygens integral to analytically describe propagation of a doughnut beam generated by a spiral phase plate.

As its last last deliverable, QUIE2T WP2 has submitted the final updates of the QIPC Strategic Report (v. 1.8) and the Quantum Information Classification scheme QICS (v. 1.3). A detailed report on the update is available from the WP2 deliverables page (deliverable D2.2.2).

We study the driven-dissipative dynamics of photons interacting with an array of micromechanical membranes in an optical cavity. Periodic membrane driving and phonon creation result in an effective photon-number-conserving nonunitary dynamics, which features a steady state with long-range photonic coherence. If the leakage of photons out of the cavity is counteracted by incoherent driving of the photonic modes, we show that the system undergoes a dynamical phase transition to the state with long-range coherence.

We investigate dissipation-induced p-wave paired states of fermions in two dimensions and show the existence of spatially separated Majorana zero modes in a phase with vanishing Chern number. We construct an explicit and natural model of a dissipative vortex that traps a single of these modes, and establish its topological origin by mapping the problem to a chiral one-dimensional wire where we observe a nonequilibrium topological phase transition characterized by an abrupt change of a topological invariant (winding number).

We discuss the preparation of many-body states of cold fermionic atoms in an optical lattice via controlled dissipative processes induced by coupling the system to a reservoir. Based on a mechanism combining Pauli blocking and phase locking between adjacent sites, we construct complete sets of jump operators describing coupling to a reservoir that leads to dissipative preparation of pairing states for fermions with various symmetries in the absence of direct inter-particle interactions. We discuss the uniqueness of these states, and demonstrate it with small-scale numerical simulations.