Detailed programme

Monday, February 23rd

10.00–10.45 Registration and Coffee (11th floor of the Physics Institute)

10.45–11.15 Welcome information (Lecture Hall 1, 1st floor of the Physics Institute)

11.15–12.45 LECTURE – Introduction to many particle quantum theory (1/4)

Mark Fannes

15.00–15.45 PARTICIPANT CONTRIBUTION – Exciton transport and dissociation in organic photovoltaics

Irene Burghardt (Goethe-Universität, Frankfurt)

15.45–16.30 PARTICIPANT C ONTRIBUTION – Multiple scattering of interacting bosons in weakly random media

Thomas Wellens (Albert-Ludwigs Universität Freiburg)

In this talk, I will give an overview of our works on multiple scattering of interacting bosons in random media. Starting first with the non-interacting case, the effects of coherent backscattering and weak localization are introduced as the main interference corrections to diffusive transport in weak disorder. Then, I will extend the underlying theoretical concepts (ladder and crossed diagrams) to the case of many interacting particles (beyond the mean field approximation), and derive nonlinear transport equations which finally characterize the effect of interactions on diffusive transport and coherent backscattering. Furthermore, I will show that, by combining many-particle transport theory with quantum optical methods, our theory is also able to describe multiple scattering of intense laser light by dilute clouds of cold atoms.

Tuesday, February 24^th

09.15–10.45 LECTURE – Introduction to many particle quantum theory (2/4)

Mark Fannes

11.15–12.45 LECTURE – Towards many-particle experiments with neutral atoms (1/2)

Andrea Alberti

15.00–15.45 PARTICIPANT CONTRIBUTION – Nonequilibrium dynamics of open systems: Quantum memory effects and nonlocal correlations

Heinz-Peter Breuer (Albert-Ludwigs Universität Freiburg)

The dynamics of open quantum systems is usually modeled by means of Markovian processes in which the open system irretrievably loses information to its surroundings. However, open systems in structured environments often show a rich and complex dynamics: In addition to purely classical effects like the dissipation of energy and the relaxation of populations to a thermal equilibrium or nonequilibrium stationary state, the time evolution features genuine quantum effects such as the decay and revival of quantum coherences, correlations, and entanglement. Such a behavior is characterized by a flow of information from the environment back to the open system. This backflow of information implies the presence of memory effects and represents the key feature of non-Markovian quantum dynamics. We will explain the general theoretical characterization and quantification of non-Markovianity in the quantum regime, and discuss recent experiments which allow to control the information flow between system and environment and to monitor the transition from the Markovian to the non-Markovian regime. Moreover, we will develop schemes for the detection of system-environment correlations, and introduce the concept of nonlocal memory effects in composite open systems.

15.45–16.30 PARTICIPANT CONTRIBUTION – Photocatalytic water decomposition on Ti(OH)_4 and dimers

Fermin R. Hernandez (Technische Universität Dresden)

The photocatalytic process of water splitting on small molecular clusters, resembling a TiO_2 surface of a photocatalyst, is studied within a DFT computational approach. Different pathways for the reaction mechanism are considered. Anionic systems are taking into account in some of these pathways, they address the same process when the surface is sensitized. Different initial structures are used for the water decomposition: Ti(OH)_4 , Ti(OH)_3 -O-Ti(OH)_3 and Ti(OH)_2-O_2-Ti(OH)_2. Representative structures of the pathways, its corresponding energy barriers and comparisons between them and a previous theoretical work [Z. Fang and D. A. Dixon, J. Phys. Chem. A 2013, 117, 3539-3555] are presented.

Wednesday, February 25^th

09.15–10.45 LECTURE – Introduction to many particle quantum theory (3/4)

Mark Fannes

11.15–12.45 LECTURE – Towards many-particle experiments with neutral atoms (2/2)

Andrea Alberti

15.00–16.30 LECTURE – Summing paths in Fock space: the semiclassical approach to many body interference (1/4)

Juan-Diego Urbina

17.00–17.45 PARTICIPANT CONTRIBUTION – Quantum reflection of antihydrogen from the Casimir-Polder potential

Gabriel Dufour (Université Pierre et Marie Curie)

Atoms or antiatoms in the vicinity of a material medium interact with that medium via the fluctuations of the electromagnetic field and experience a Casimir-Polder force. Contrary to the classical expectation, an atomic wavepacket incident on the attractive Casimir-Polder potential is partly reflected in the quantum regime. This quantum reflection is relevant to experiments such as GBAR where cold antihydrogen atoms will be dropped on an annihilation plate with the aim of measuring the gravitational acceleration of antimatter. I will present realistic estimates of the Casimir-Polder potential and quantum reflection probability for an antihydrogen atom incident on a material slab, taking into account the specificities of antihydrogen and the optical properties of the slab. The quantum reflection probability turns out to be markedly affected by the composition of the slab. In particular, quantum reflection is enhanced on a medium interacting weakly with the electromagnetic field. This counter-intuitive effect is better understood by mapping the problem of reflection on an attractive well onto that of reflection on a repulsive wall. Highly reflective materials could be used to trap and guide cold antihydrogen with material walls and allow a more precise study of the gravitational properties of antimatter. With this in mind we computed reflection probabilities on thin silica slabs, graphene and nanoporous media. For the latter we use an effective medium model and show a dramatic increase of the reflection probability as the porosity of the medium increases.

Thursday, February 26^th

09.15–10.45 LECTURE – Introduction to many particle quantum theory (4/4)

Mark Fannes

11.15–12.45 RESEARCH T ALK – Ionization and Recombination in a Microwave Field

Tom Gallagher (University of Virginia)

Recent investigations of ionization of ground state atoms by high intensity laser pulses have shown that atoms are left in Rydberg states subsequent to the laser pulse. Contrary to earlier work, recent microwave ionization experiments have shown a similar phenomenon. Furthermore, laser excitation above the limit in a microwave field leads to bound atoms. The latter recombination process occurs for laser excitation at specific phases of the microwave field. Common threads of the microwave and laser experiments are identified.

15.00–16.30 LECTURE – Multiphoton interference experiments (1/2)

Fabio Sciarrino

17.00–17.45 PARTICIPANT CONTRIBUTION – Quantum Zeno dynamics of a Rydberg atom

Adrien Signoles (Universität Heidelberg)

Quantum Zeno dynamics allows one to tailor dynamically at will a system's Hilbert space. Recent proposals, particularly in the Cavity Quantum Electrodynamics (CQED) context, highlight the interest of QZD for quantum state engineering tasks. In this talk I will report the observation of QZD in the 51-dimension Hilbert space of a large angular momentum J = 25. Continuous selective interrogation limits the evolution of this angular momentum to an adjustable multi-dimensional subspace. This confined dynamics leads to the production of non-classical 'Schrödinger cat' states, quantum superpositions of angular momentums pointing in different directions.

Friday, February 27^th

09.15–10.45 LECTURE – Multiphoton interference experiments (2/2)

Fabio Sciarrino

11.15–12.45 LECTURE – Experiments on multimode interference and entanglement (1/4)

Nicolas Treps

15.00–16.30 LECTURE – Summing paths in Fock space: the semiclassical approach to many body interference (2/4)

Juan-Diego Urbina

Monday, March 2^nd

09.15–10.45  LECTURE – Summing paths in Fock space: the semiclassical approach to many body interference (3/4)

Juan-Diego Urbina

11.15–12.45  LECTURE – Multiparticle quantum transport theory (1/4)

Mattia Walschaers

15.00–16.30 RESEARCH TALK – Electronic transport through many-particle systems:the case of the transmission phase of a quantum dot

Rodolfo Jalabert (Université de Strasbourg, IPCMS)

Interaction effects critically influence the transport through very small electronic devices. At low temperatures, the current can be Coulomb-blockaded in the case of quantum dots connected through tunnel barriers to electrodes. If a quantum dot operating in the Coulomb-blockade regime is embedded in one of the arms of an Aharonov-Bohm interferometer, the transmission phase through the quantum dot can be inferred. Such phase-sensitive experiment has been performed, and it yielded a puzzling in-phase locking between consecutive Coulomb-blockade resonances peaks. We show that the spatial wave-function correlations existing in chaotic ballistic quantum dots provide a tendency for the emergence of large universal sequences of in-phase resonances in the short electron-wavelength limit. This effective one-particle description, developed from the constant-charging energy model of the Coulomb-blockade, is valid for quantum dots with at least one hundred of electrons. Smaller dots require going beyond mean-field approaches by including the effect of electronic correlations. Numerical methods, based on Density Matrix Renormalization Group, can be used to obtain the transmission phase of a strongly interacting system. Using such an approach, we demonstrate that electronic correlations do not generically lead to the in-phase behavior and that small dots are always in the regime of random relative phases.

17.00–17-45 PARTICIPANT CONTRIBUTION – Exciton Interactions in Two Dimensions

Valentin Walther (MPIPKS Dresden)

Recent experiments have shown that excitons with binding energies of up to 1 eV can be produced in a special class of two-dimensional semiconductors (so-called TMDCs). In this talk, I will discuss their level structure and present calculations of exciton interactions at asymptotic distances.

Tuesday, March 3^rd

09.15–10.45 LECTURE – Summing paths in Fock space: the semiclassical approach to many body interference (4/4)

Juan-Diego Urbina

11.15–12.45 LECTURE – Experiments on multimode interference and entanglement (2/4)

Nicolas Treps

15.00–16.30 LECTURE – Multiparticle quantum transport theory (2/4)

Mattia Walschaers

17.00–17.45 PARTICIPANT CONTRIBUTION – Multiplexed Boson Sampling with integrated photonics

Niko Viggianiello (Sapienza Università di Roma)

Boson Sampling is a computational task strongly believed to be hard for classical computers, but efficiently solvable by orchestrated bosonic interference in a specialised quantum computer. Current experimental schemes, however, are still insufficient for a convincing demonstration of the advantage of quantum over classical computation. A new variation of this task, Scattershot Boson Sampling, leads to an exponential increase in speed of the quantum device, using a larger number of photon sources based on parametric downconversion. This is achieved by having multiple heralded single photons being sent, shot by shot, into different random input ports of a interferometer. Here I’ll introduce the Scattershot Boson Sampling experiment, where six different photo pair sources are coupled to integrated photonic circuits. This approach represents an important leap towards a convincing experimental demonstration of the quantum computational supremacy.

Wednesday, March 4^th

09.15–10.45 LECTURE – Multiparticle quantum transport theory (3/4)

Mattia Walschaers

11.15–12.45 LECTURE – Experiments on multimode interference and entanglement (3/4)

Nicolas Treps

15.00–15.45 PARTICIPANT CONTRIBUTION – Phase Correlation Length and Universal OAM Entanglement Decay in Turbulence

Vyacheslav Shatokhin (Albert-Ludwigs Universität Freiburg)

We consider the propagation of two photonic qubits, initially maximally entangled in their orbital angular momenta (OAM), across a weakly turbulent atmosphere. By introducing the phase correlation length of an OAM beam, we show that the photonic entanglement exhibits a universal exponential decay.

15.45–16.30  PARTICIPANT CONTRIBUTION – Memory effects in a qubit coupled to a generic environment: divisibility and distinguishability

Moisés Carrera (UNAM, Cuernavaca, Mexico)

We analyze a two level quantum system (qubit) which is interacting with a environment, the last one is modeled by a Gaussian Unitary Ensemble (GUE). We study the divisibility of the quantum channel and the distinguishability of the states of the qubit. Such properties are related to the memory effects and then to the quantum non-Markovianity. We will show that this kind of environment induced strong memory effects on the open system.

17.00–17.45  PARTICIPANT CONTRIBUTION – TBA

Benedikt Kloss (Goethe-Universität, Frankfurt, Germany)

Thursday, March 5^th

09.15–10.45 LECTURE – Multiparticle quantum transport theory (4/4)

Mattia Walschaers

11.15–12.45 LECTURE – Experiments on multimode interference and entanglement (4/4)

Nicolas Treps

15.00–15.45 PARTICIPANT CONTRIBUTION -

Quantum-to-classical transition in the Anderson model

Clemens Gneiting (Albert-Ludwigs Universität Freiburg)

The problem of single- and many-particle transport through disordered media lies at the heart of a multitude of physical processes. A prominent consequence of disorder is that the propagation of particles may be hindered by destructive interference, a phenomenon known as Anderson localization. We investigate how this transition into localized asymptotic states takes place. In particular, we focus on single- and many-particle coherence properties and their evolution in the ensemble average. We find that, upon averaging over the disorder realizations, the effective time evolution of arbitrary initial states exhibits a dephasing process towards their Anderson-localized asymptotic limit, for

instance indicated by the decreasing visibility of an interference pattern. We characterize this dephasing process in terms of quantum master equations for the case of a single and two particles in a discrete lattice with a disordered potential and different initial states.

15.45–16.30 PARTICIPANT CONTRIBUTION – Decoherence in a tripartite system

Hector Moreno (UNAM, Cuernavaca, Mexico)

For many experimental quantum information devices, the central system is  well isolated against simple decoherence processes, but it is subject to some  imperfections in the apparatus. To describe this situation, we use a tripartite system which consist of a central system, near environment and a heat bath, this in  order to analyze the decoherence of the central system for different values of the coupling between the near and far environments.

17.00–17.45 PARTICIPANT CONTRIBUTION – TBA

TBA