Conferences

Program and list of abstracts: HERE.

Topics:

• Anderson localization & transition
• Topological insulators
• 2D metal-insulator transition & electron interaction
• Many body-localisation
• Integer quantum Hall systems
• Non-Hermitian systems
• Cold atoms
• Weyl semimetals

Talk: Measurement-induced transition in random quantum circuits: from stroboscopic to continuous
M. Szyniszewski, A. Romito, H. Schomerus

Talk: Localisation, ergodicity, and quantum measurements

Talk: Entanglement transition from variable-strength weak measurements
M. Szyniszewski, A. Romito, H. Schomerus

Topics:

• Foundations of quantum mechanics
• Quantum measurement in information processing
• Quantum measurements in nanodevices
• Quantum measurement and thermodynamics
• Quantum metrology and precision measurements

Topics:
1. Statistical Mechanics: from foundations to quantum information.
2. Numerical methods: high-level programming and advanced numerical methods.
3. Coherent dynamics: entanglement, decoherence, phase transitions, driven systems.
4. Topological quantum matter: phases and diagnostics.
5. Physical implementations: cold atoms, trapped ions, nanophysics, materials.

Lecturers:
F. Alet (CNRS, Toulouse, France)
E. Andrei (Rutgers University, US)
B. Beri (University of Cambridge, UK)
I. Bloch (MPQ, Garching, Germany)
P. Calabrese (SISSA, Trieste, Italy)
J. Chalker (University of Oxford, UK)
X. Chen (Caltech, US)
J. Dalibard (College de France, Paris, France)
M. Devoret (Yale University, US)
D. Dhar (Indian Institute of Science Education and Research, Pune)
M. Heyl (MPIPKS Dresden, Germany)
V. Khemani (Harvard University, US)
W. Krauth (Ecole Normale Superieure, Paris, France)
B. Lake (Berlin Technical University, Germany)
C. Laumann (Boston University, US)
A. Lazarides (MPIPKS Dresden, Germany)
A. MacKenzie (MPI-CPfS Dresden, Germany)
E. Martinez (University of Copenhagen, Denmark)
U. Schollwoeck (LMU Munich, Germany)
M. Znidaric (University of Ljubljana, Slovenia)

Topics:

• Modern Applications of Random Permutations
• Random Matrices and Quantum Symmetries
• Applications of Probability in Statistical Learning Theory

Topics:

• Floquet engineering (Andre Eckardt)
• Topological order and anyons (Belen Paredes)
• Chern numbers counted in a synthetic-dimension quantum Hall strip (Ian B. Spielman)
• Realization of gauge fields in quantum gases (Ian B. Spielman)
• Topological insulators (Jan Carl Budich)
• Experimental realization of Chern insulators / Gauge fields in optical lattices (Monika Aidelsburger)
• Floquet topological insulators in photonic wave-guides (Alexander Szameit)
• Fractional Chern insulators and Methods (Frank Pollmann)
• Floquet states of irradiated electrons in topological solid-state systems (Fahad Mahmood)

Lecturers (and preliminary topics):

• Philippe Corboz (Amsterdam): Projected entangled pair states (PEPS) (introduction)
• Olivier Parcollet (Saclay): Dynamical Mean Field Theory (DMFT) and impurity solvers
• Lode Pollet (LMU): Quantum Monte Carlo methods
• Ulrich Schollwoeck (LMU): Matrix product states (MPS), Density matrix renormalization group (DMRG)
• Norbert Schuch (MPQ): PEPS (mathematical aspects)
• Andreas Weichselbaum (LMU): Numerical renormalization group (NRG)
• Steve White (UC Irvine): DMRG in two dimensions

Poster: Charge-density-wave phases of a one-dimensional model with long-range repulsive interactions

Poster: Charge-density-wave phases of a one-dimensional model with long-range repulsive interactions

Abstract:
The one-dimensional extended t-V model on a lattice describes fermions with repulsive interactions of finite range and exhibits a quantum phase transition between a Luttinger liquid conducting phase and a Mott insulating phase. Its properties make it useful in the description of candidate materials for Mott transistor devices. It is known that by tailoring the potential energy of the insulating system, one can force a phase transition into a different insulating phase [1, 2]. We show how to construct all possible charge-density-wave phases of the system at low critical densities in the atomic limit. Higher critical densities are investigated by a brute-force analysis of the possible finite unit cells of the Fock states. We present example phase diagrams of the system.

We construct a matrix product operator representation of the Hamiltonian of the t-V model. Using the matrix product states (MPS) approach we go beyond the atomic limit, where the phase diagrams are much richer. MPS method is especially problematic near the transition between two different charge-density-wave phases and we show how the bond dimension must be increased in order to converge the results.

Our results indicate that the number of possible insulating phases grows with both the maximum interaction range and the fermion density and may cause the loss of insulating properties of the material at finite temperatures.

References:
[1] P. Schmitteckert and R. Werner, Phys. Rev. B, 69, 195115 (2004).
[2] T. Mishra, J. Carrasquilla, and M. Rigol, Phys. Rev. B, 84, 115135 (2011).

Talk: Effects of strain in graphene/hexagonal-boron-nitride heterostructures
M. Szyniszewski, E. Mostaani, N.D. Drummond, V.I. Fal'ko

Poster: Fermions with long-range interactions using a matrix-product-states approach

Abstract:
The long-range t-V model of fermions on a lattice is known to exhibit a transition between a Luttinger liquid phase and a Mott insulator phase [1]. At insulating densities, one can tailor the potential energy of the model in such a way that one forces a quantum phase transition to either another insulating charge-density-wave phase, a bond-order phase or a Luttinger liquid [2]. We show how to construct a matrix product operator representation of the Hamiltonian of the t-V model and we present phase diagrams calculated using the matrix-product-states approach [3]. We compare these phase diagrams with results obtained in the atomic limit.

References:
[1] G. Gomez-Santos, Phys. Rev. Lett. 70, 3780 (1993).
[2] P. Schmitteckert and R. Werner, Phys. Rev. B 69, 195115 (2004); T. Mishra et al., Phys. Rev. B 84, 115135 (2011).
[3] D. Perez-Garcia et al., Quantum Inf. Comput. 7, 401 (2007); F. Verstraete et al., Adv. Phys. 57, 143 (2008).

Talk: Diffusion Monte Carlo study of charge carrier complexes in two-dimensional semiconductors
M. Szyniszewski, E. Mostaani, C. Price, R. Maezono, N. Drummond, V. Fal'ko

Talk: Diffusion Monte Carlo study of charge carrier complexes in two-dimensional semiconductors
M. Szyniszewski, E. Mostaani, C. Price, R. Maezono, N. Drummond, V. Fal'ko

Talk: Diffusion Monte Carlo study of charge carrier complexes in two-dimensional semiconductors
M. Szyniszewski, E. Mostaani, N. Drummond, V. Fal'ko

Abstract:
We use a novel description of the interaction between charges in two-dimensional (2D) semiconductors to investigate the binding properties of two-, three- and four-particle complexes of charge carriers (excitons, trions and biexcitons). We report binding energies and pair distribution functions calculated using diffusion quantum Monte Carlo methods, which are exact for these systems. Our results will enable the interpretation of experimental photoabsorption and photoluminescence measurements on 2D transition-metal dichalcogenide materials. We show that our data are consistent with previous binding-energy data for the limits in which the interactions between charges reduce to logarithmic and Coulomb (1/r) forms. We find that the logarithmic interaction that has previously been used to study excitons and trions in 2D semiconductors provides an inadequate description of the behaviour of systems such as molybdenum disulphide, and we provide accurate binding-energy data for excitons, trions and biexcitons in these materials.

Poster: Strong coupling expansion of the $t$-$V$ model (further results)
M. Szyniszewski, E. Burovski

Abstract:
We employ a strong coupling expansion - similar to the one used in the lattice field theory studies [1] - to solve the one-dimensional extended $t$-$V$ model of fermions on a lattice [2]. This model is solved for a range of filling factors, including both commensurate - where a charge density wave is present - and incommensurate densities. The first set consists not only of a trivial case of half filling. The method allows us to trace the transition from a Luttinger liquid phase to a Mott insulating phase and calculate the critical parameter $K$. This simple yet powerful method is not based on Bethe ansatz and it works for both integrable and non-integrable systems. Furthermore, we investigate how tailoring the interaction can introduce other ordered phases of the system [3].

References:
[1] C.J. Hamer, Phys. Lett. B 82, 75-78 (1979); D.P. Crewther, C.J. Hamer, Nucl. Phys. B 170, 353-368 (1980).
[2] G. Gomez-Santos, Phys. Rev. Lett. 70, 3780 (1993); R.G. Dias, Phys. Rev. B 62, 7791 (2000).
[3] P. Schmitteckert, R. Werner, Phys. Rev. B 69, 195115 (2004); T. Mishra et al., Phys. Rev. B 84, 115135 (2011).

Topics:

• matrix product states (MPS)
• projected entangled pair states (PEPS)
• multiscale entanglement renormalization ansatz (MERA)

Poster: Generalised $t$-$V$ model in one dimension
M. Szyniszewski, E. Burovski

Abstract:
We use a strong coupling expansion [1] to solve the one-dimensional extended $t$-$V$ model of fermions [2,3]. The model is solved for a range of densities, including both commensurate - where a charge density wave is present - and incommensurate densities. The first set consists not only of a trivial case of half filling. The method allows us to trace the transition from a Luttinger liquid phase to a Mott insulating phase. This simple yet powerful method is not based on Bethe ansatz and it works for both integrable and non-integrable systems.

References:
[1] C.J. Hamer, Phys. Lett. B 82, 75-78 (1979).
[2] G. Gomez-Santos, Phys. Rev. Lett. 70, 3780 (1993).
[3] R.G. Dias, Phys. Rev. B 62, 7791 (2000).

Talk: Lattice Hamiltonian approach to the Schwinger model
K. Cichy, A. Kujawa-Cichy, M. Szyniszewski

Abstract:
We employ exact diagonalization with strong coupling expansion to the massless and massive Schwinger model. For the massless case, this allows us for a high accuracy continuum limit estimation of the ground state energy and scalar and vector mass gaps with precisions of the order of one part per billion or better. Furthermore, we investigate the chiral condensate and compare our calculations to previous results available in the literature. Oscillations of the chiral condensate which are present while increasing the expansion order are also studied and are shown to be directly linked to the presence of flux loops in the system.

Activities:

• making graphene and playing with models of carbon materials
• crystallography: how a shadow of a 3D shape can change depending on the angle

Activities:

• making graphene
• crystallography: making shapes and looking at their shadows

Activities:

• hydrophobic sand
• making graphene

Activities:

• hydrophobic sand and coat
• LEGO magnetic force microscope
• making graphene
• ferrofluids