Condensed Matter Physics Seminar
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2022-06-10 (Friday)
join us at 12:15 
Carlos Mejuto Zaera (SISSA, Trieste)Perspective on Selected Configuration Interaction: From Molecules to Solids (ONLINE)
The study of strong correlation in model Hamiltonians has produced a varied palette of results which promise exciting applications for material design. Still, bridging the computational description of simple models with realistic _ab initio_ Hamiltonians presents outstanding challenges, particularly with respect to the accurate yet affordable approximation of multi-orbital models. In this talk, I will give a bird's eye view on our recent efforts to push on some of these numerical issues, which draw inspiration from traditional techniques from the computational chemistry community. In particular, I will discuss the use of simple (and some less simple) variants of selected Configuration Interaction (sCI) to efficiently compute one-body Green functions, with direct application as impurity solvers in Hamiltonian-based DMFT. We will go over the basic heuristic of the algorithm, briefly visit a couple of representative applications in solid state and chemical physics, as well as an honest portrayal of the challenges it faces and how one may alleviate them. For the meeting link contact Pawel Jakubczyk.
2022-06-03 (Friday)
join us at 16:15
Robert Konik (Brookhaven National Lab)Post-Quantum Quench Growth of Renyi Entropies in Perturbed Luttinger Liquids (ONLINE, HOUR CHANGED !!!)
The growth of Renyi entropies after the injection of energy into a correlated system provides a window upon the dynamics of its entanglement properties. We provide here a scheme by which this growth can be determined in Luttinger liquids systems with arbitrary interactions, even those introducing gaps into the liquid. This scheme introduces the notion of a generalized mixed state Renyi entropy. We show that these generalized Renyi entropies can be computed and provide analytic expressions thereof. Using these generalized Renyi entropies, we provide analytic expressions for the short time growth of the second and third Renyi entropy after a quantum quench of the coupling strength between two Luttinger liquids, relevant for the study of the dynamics of cold atomic systems. For longer times, we use truncated spectrum methods to evaluate the post-quench Renyi entropy growth. For the meeting link contact Pawel Jakubczyk or Milosz Panfil.
2022-05-27 (Friday)
join us at 12:15
Pierbiagio Pieri (University of Bologna)FFLO correlations in polarized ultracold Fermi gases (ONLINE)
Quite generally, an imbalance between the densities of spin-up and spin-down fermions hinders pairing and superfluidity in two-component attractive Fermi gases. The Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase, in which pairs condense at a finite value of center-of-mass momentum to compensate for the mismatch of the two Fermi surfaces, was proposed many years ago as a possible superfluid phase compatible with a finite polarization. In this talk, I will discuss how significant precursor FFLO fluctuation effects appear already in the normal phase of polarized Fermi gases, and how they could be observed experimentally. At zero temperature, I will also discuss how the quasi-particle parameters of the normal Fermi gas are changed when approaching an FFLO quantum critical point. Within a fully self-consistent t-matrix approach, we find that the quasi-particle residues vanish and the effective masses diverge at the FFLO quantum critical point, with a complete breakdown of the quasi-particle picture that is similar to what is found in heavy-fermion materials at an antiferromagnetic quantum critical point. For the meeting link contact Pawel Jakubczyk.
2022-05-20 (Friday)
join us at 12:15
Matthieu Tissier (Sorbonne, Paris)The random field Ising model: equilibrium, and out-of-equilibrium, properties (ONLINE)
The aim of this presentation is to convey the audience to an overview of the Random Field Ising Model (RFIM), a paradigmatic system in the field of statistical mechanics in the presence of quenched disorder. I will first discuss several experimental realizations that were considered in the past. I will then present the remarkable results obtained back in the 70's, in particular the famous dimensional reduction property, discovered by Parisi and Sourlas. I will comment on the controversy that emerged at that time.In the second part of the talk , I will give a summary of the work that I did, in collaboration with G. Tarjus. I will give the main necessary ingredients (functional renormalization-group, nonperturbative renormalization group) and give our main results. For the seminar link contact Pawel Jakubczyk.
2022-05-13 (Friday)
room 1.02, Pasteura 5 at 12:15
Krzysztof Jachymski (IFT UW)Quantum simulations of exotic lattice models in ultracold hybrid systems
Ultracold atomic systems can be precisely controlled in experiment, allowing for realization of a wide class of Hamiltonians and studying both their ground state properties and dynamics. A lot of results have been obtained utilizing optical lattices which provide ideal crystal structures for neutral atoms. Optical tweezer arrays combined with Rydberg excitations have recently become the new star in the field. I will discuss the possibilities offered by tweezer setups and an idea for increasing the versatility of the system by adding more atomic species.
2022-04-29 (Friday)
room 1.02, Pasteura 5 at 12:15
Andrzej Chlebicki (IFT UW)The low-temperature phase of the O(N) models below two dimensions
2022-04-22 (Friday)
room 1.02, Pasteura 5 at 12:15
Enej Ilievski (Univ. of Ljubljana)Anomalous transport laws in many-body dynamical systems
Our understanding of non-equilibrium phenomena in quantum many-body systems has tremendously progressed in the past decade. The study of interacting quantum matter constrained to low spatial dimensions has been at the forefront of theoretical research, owing primarily to the development of powerful analytical tools and efficient numerical simulations. The interest has been further amplified by the plethora of experimental advancements in the cold-atom techniques, now finally permitting to directly probe complex relaxation processes with a high degree of accuracy. In this talk, I will discuss a few prominent examples of non-ergodic many-body interacting systems that feature unorthodox dynamical properties and highlight the phenomenon of spin superdiffusion.
2022-04-01 (Friday)
join us at 12:15
Andrea Trombettoni (SISSA, Trieste)Floquet Hamiltonians for Tilted 1D Bose Gases (Online)
After an introduction to 1D ultracold gases and their coherence properties, I discuss how to implement an integrable Floquet Hamiltonian for a periodically tilted 1D Bose gas. In general, an integrable model subjected to a periodic driving gives rise to a non-integrable Floquet Hamiltonian. Here we show that the Floquet Hamiltonian of the integrable Lieb-Liniger model in presence of a linear potential with a periodic time-dependent strength is instead integrable and its quasi-energies can be determined using the Bethe ansatz approach. We discuss various aspects of the dynamics of the system at stroboscopic times and we also propose a possible experimental realizationof the periodically driven tilting in terms of a shaken rotated ring potential. We also discuss the micro-motion operator and the expression for a generic time evolved state of the system. To conclude, a discussion of the applications to atomtronics is presented. For the seminar link contact Pawel Jakubczyk.
2022-03-25 (Friday)
join us at 12:15
Nicolò Defenu (ETH Zurich)Quantum criticality and out-of-equilibrium scaling long-range systems and beyond
The seminar is meant to present a bird's eye view on the field of long-range interacting quantum systems. The talk will start with a brief overview of critical phenomena in systems with power law interactions 1/r^{\alpha} showing how the equilibrium scaling depends of the power-law scaling $\alpha$. Then, I will describe the peculiar out-of-equilibrium scaling dynamics observed in "strong" long-range systems with \alpha < d, both for sudden and slow quenches. Finally, I will show how the study of long-range interacting systems is connected to the case of non-homogeneous disordered structures. For the seminar link contact Pawel Jakubczyk.
2022-03-18 (Friday)
join us at 12:15
Alessio Squarcini (Max Planck Stuttgart & University of Stuttgart)Beyond Derrick’s theorem: vortex mass in the three-dimensional XY model
The three-dimensional XY model describes the universal properties of Helium at its superfluid transition. The attempts to define a mass of vortices in superfluids faced, in particular, the difficulty of a divergence that is a particular case of Derrick’s theorem for classical field theories. We show that nearby the XY critical point, where fluctuations dominate and classical field theory does not apply, the vortex exists as a fundamental topological excitation with a finite mass. We exhibit perfect agreement between high precision Monte Carlo simulations and exact analytic determinations of magnetization and energy density profiles, and in the process determine the mass of the vortex excitation. Before presenting the results for the 3D-XY model this talk will expose an introductory overview of the exact theory of phase separation and interfacial phenomena and its extension to three-dimensional systems. To obtain the meeting link, contact Pawel Jakubczyk.