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The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community.   [ More information ]


Upcoming Seminars
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Monday 4 July 2022, 10:45 at LPTMC, salle 523 du LPTMC - Tour 12-13 Jussieu SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat
Kirill Polovnikov Constrained fractal polymer chain in curved geometry: how far is KPZ?
Abstract: Can intrinsic curvature of the space yield a similar regime of fluctuations as a certain type of random potentials? In this talk by means of scaling analyses of the free energy and computer simulations I will discuss stretching of a fractal polymer chain around a disc in 2D (or a cylinder in 3D) of radius R. The typical excursions of the polymer away from the surface scale as $\Delta \sim R^{\beta}$, with the Kardar-Parisi-Zhang (KPZ) growth exponent $\beta=1/3$ and the curvature-induced correlation length is described by the KPZ exponent z=3/2. Remarkably, the uncovered KPZ scaling is independent of the fractal dimension of the polymer and, thus, is universal across the classical polymer models, e.g. SAW, randomly-branching polymers, crumpled unknotted rings. The one-point distribution of fluctuations, as found in simulations, can be well described by the squared Airy law, connecting our 2D polymer problem with the (1+1)D Ferrari- Spohn universality class of constrained random walks. A relation between directed polymers in quenched random potential (KPZ) and stretched polymers above the semicircle will be explained.

Tuesday 5 July 2022, 11:00 at LPTMS, Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530
( For zoom info, please write to valentina.ros@universite-paris-saclay.fr or check LPTMS website )
LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay)) cond-mat.stat-mech
Thomas Barthel ( Duke University ) Crossover functions for entanglement entropy in many-body energy eigenstates and universality
Abstract: We consider the entanglement entropies of energy eigenstates in quantum many-body systems. For the typical models that allow for a field-theoretical description of the long-range physics, we find that the entanglement entropy of (almost) all eigenstates is described by a single crossover function. The eigenstate thermalization hypothesis (ETH) implies that such crossover functions can be deduced from subsystem entropies of thermal ensembles and that they assume universal scaling forms in quantum-critical regimes. They describe the full crossover from the groundstate entanglement scaling for low energies and small subsystem size (area or log-area law) to the extensive volume-law regime for high energies or large subsystem size. For critical 1d systems, the scaling function follows from conformal field theory (CFT). We use it to also deduce the scaling function for Fermi liquids in d>1 dimensions. These analytical results are complemented by numerics for large non-interacting systems of fermions in d=1,2,3 and the harmonic lattice model (free scalar field theory) in d=1,2. Lastly, we demonstrate ETH for entanglement entropies and the validity of the scaling arguments in integrable and non-integrable interacting spin chains. [1] « Eigenstate entanglement: Crossover from the ground state to volume laws”, Phys. Rev. Lett. 127, 040603 (2021) [2] « Scaling functions for eigenstate entanglement crossovers in harmonic lattices », Phys. Rev. A 104, 022414 (2021) [3] « Eigenstate entanglement scaling for critical interacting spin chains”, Quantum 6, 642 (2022)

Tuesday 5 July 2022, 14:00 at LPTHE, Library 4th floor and online (link in comments)
( https://cnrs.zoom.us/j/98061606464?pwd=NlBxVHJiUm5YQjdKdWkxY05XVlltQT09 )
LPTHE-PPH (Particle Physics at LPTHE) astro-ph|hep-ph|hep-th
Giacomo Landini ( University of Valencia ) Macroscopic Dark Matter from a dark confining phase transition
Abstract: First order phase transitions can leave relic pockets of false vacua and their particles, that manifest as macroscopic Dark Matter. I present one predictive model: a gauge theory with a dark quark relic heavier than the confinement scale. During the first order phase transition to confinement, dark quarks remain in the false vacuum and get compressed, forming Fermi balls that can undergo gravitational collapse to stable dark dwarfs (gravitational bound states analogous to white dwarfs) near the Chandrasekhar limit, or primordial black holes. Dark Matter manifests as a macroscopic object made of dark particles.

Tuesday 5 July 2022, 15:00 at LPTMC, Jussieu towers 12/13 room 523 (5th floor) SEM-INFOR (Séminaire informel) cond-mat.mes-hall
Zohar Nussinov ( Washington University in St Louis ) D-dimensional gauge like symmetries, dualities, and topological orders
Abstract: We introduce and discuss aspects of "d-dimensional gauge-like symmetries" (also often referred to as "higher" or "subsystem symmetries''). We show how such symmetries may lead to dimensional reductions. In particular, we discuss the effects of thermal fluctuations using a generalization of Elitzur's theorem. We describe how these symmetries can lead to topological orders and illustrate that, depending on the system geometry, there are both quantum and classical systems that have degeneracies that depend on the system topology or are exponentially large in the system boundary area. We will then briefly discuss the "bond algebraic" approach to dualities and explain why dualities are often conformal. Using this approach, we illustrate that the nearest neighbor "XXZ honeycomb compass" (a two component (XY) analog of the Kitaev model on the honeycomb lattice) and square lattice Majorana Hubbard model both exhibit exact 3D Ising type transitions. With these dualities, we compute the free energies of the X-cube model and other topologically ordered systems.

Wednesday 6 July 2022, 13:45 at LKB, Collège de France, site Marcelin-Berthelot, salle 2 - Paris 5 SEM-LKB (Séminaire du Laboratoire Kastler Brossel) quant-ph
Andreas Wallraff ( Department of Physics, ETH Zurich, Switzerland ) Realizing Quantum Error Correction with Superconducting Circuits
Abstract: Superconducting electronic circuits are ideally suited for studying quantum physics and its applications. Since complex circuits containing hundreds or thousands of elements can be designed, fabricated, and operated with relative ease, they are one of the prime contenders for realizing quantum computers. Currently, both academic and industrial labs vigorously pursue the realization of universal fault-tolerant quantum computers. However, building systems which can address commercially relevant computational problems continues to require significant conceptual and technological progress. For fault-tolerant operation quantum computers must correct errors occurring due to unavoidable decoherence and limited control accuracy. Here, we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit we encode quantum information in a distance-three logical qubit building up on our recent distance-two error detection experiments [1]. In an error correction cycle taking only 1.1 µs, we demonstrate the preservation of four cardinal states of the logical qubit. Repeatedly executing the cycle, we measure and decode both bit- and phase-flip error syndromes using a minimum-weight perfect-matching algorithm in an error-model-free approach and apply corrections in postprocessing. We find a low logical error probability of 3 % per cycle [2]. The measured characteristics of our device agree well with a numerical model. Our demonstration of repeated, fast, and high-performance quantum error correction cycles, together with recent advances in ion traps, support our understanding that fault-tolerant quantum computation will be practically realizable. [1] C. Kraglund Andersen et al., Nature Physics 16, 875–880 (2020) [2] S. Krinner, N. Lacroix et al., Nature 605, 669–674 (2022) * Work done in collaboration with Sebastian Krinner, Nathan Lacroix, Ants Remm, Agustin Di Paolo, Elie Genois, Catherine Leroux, Christoph Hellings, Stefania Lazar, Francois Swiadek, Johannes Herrmann, Graham J. Norris, Christian Kraglund Andersen, Markus Müller, Alexandre Blais, Christopher Eichler, and Andreas Wallraff

Thursday 7 July 2022, 14:00 at LPTHE, Seminar room at LPTMC towers 13-12 room 523 (5th floor) TQM (Theory of quantum matter) math-ph
Gregory Fiete ( Northeastern university, Boston ) Manipulation of magnetic order and band topology through selective phonon excitation
Abstract: Quantum materials driven out-of-equilibrium by a laser pump offer new opportunities for exploring intriguing quantum phenomena, including electron-correlation behaviors and topological properties of excitations. After reviewing some recent motivating pump-probe experiments, I will turn to our theoretical studies of driven many-body quantum systems. I will place particular emphasis on the situation where the laser frequency is chosen to selectively excite particular phonon modes and describe the impact of the non-equilibrium lattice on the electron properties, such as magnetism and band topology. The layered van der Waals materials CrI3 and MnBi2Te4 serve as excellent examples of the broader phenomena one might expect. I will also describe how hybrid phonon-magnon excitations in insulating antiferromagnets can exhibit highly tunable topological transitions in the presence of an externally applied magnetic field. The talk will conclude with an outlook for the prospects of achieving other interesting many-body phenomena in driven materials.

Monday 11 July 2022, 10:45 at LPTMC, salle 523 du LPTMC - Tour 12-13 Jussieu SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat
Thomas Franosch ( Universität Innsbruck ) TBA

Monday 11 July 2022, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-PHM (Séminaire de physique mathématique) math-ph
Andrea Cappelli ( INFN and Department of Physics, Florence, Italy ) Surface excitations of 3d Topological Insulators: conformal invariance, self-duality and bosonization
Abstract: Massless fermions and anyons on the surface of (3 1)-dimensional topological insulators can be described at the semiclassical level by a non-local Abelian gauge theory involving two gauge fields. The theory is non-trivial owing to its solitonic excitations with electric and magnetic charges. We compute the partition function and the solitonic spectrum, thus showing conformal invariance and electric-magnetic self-duality. This theory also provides a framework for semiclassical bosonization of (2 1)d fermions.

Tuesday 12 July 2022, 11:00 at LPTMS, Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530
( For zoom info, please write to valentina.ros@universite-paris-saclay.fr or check LPTMS website )
LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay)) cond-mat.stat-mech
Thomas Franosch ( University of Innsbruck ) Gravitaxis of a single active particle
Abstract: The active Brownian particle (ABP) model has become a paradigm for dynamics far from equilibrium and has attracted considerable attention in the statistical-physics/soft-matter community [1,2]. In this model particles undergo directed motion along their axis of orientation which is subject to orientational diffusion. While it is rather easy to simulate the dynamics of such agents in a prescribed potential landscape, analytical progress even for the simplest set-ups has been difficult. Here I present an exact solution for the dynamics of active Brownian particle in a uniform gravitational field as described by the equations of motion of Ref. [3]. We show that the problem maps to the noisy overdamped pendulum or dynamics in a tilted washboard potential. Close to the underlying classical bifurction we unravel a resonance for the diffusion coefficient. We derive the corresponding Fokker-Planck equation and use techniques familiar from quantum mechanics to provide a complete solution. The scaling behavior at the resonance is rationalized in terms of a simple harmonic oscillator picture. [1] Clemens Bechinger, Roberto Di Leonardo, Hartmut Löwen, Charles Reichhardt, Giorgio Volpe, and Giovanni Volpe, Active particles in complex and crowded environments, Rev. Mod. Phys. 88, 045006 (2016). [2] C. Kurzthaler, C. Devailly, J. Arlt, T. Franosch, W. C. K. Poon, V. A. Martinez, and A. T. Brown, Probing the spatiotemporal dynamics of catalytic janus particles with single-particle tracking and differential dynamic microscopy, Physical Review Letters 121, 078001 (2018). [3] B. ten Hagen, F. Kümmel, R. Wittkowski, D. Takagi, H. Löwen, and C. Bechinger, Gravitaxis of asymmetric self-propelled colloidal particles, Nature Communications 5, 4829 (2014).

Tuesday 12 July 2022, 13:30 at LPENS, Conf IV LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
Stephan Roche ( ICREA / ICN2, Barcelona ) Topological Spin Transport in Quantum Materials & Entanglement Dynamics
Abstract: In this talk, I will present theoretical spin transport features in Quantum Materials such as MoTe2 and WTe2-based materials which have recently been the subject of great attention within the broad context of Topological Quantum Matter [1]. By focusing on the monolayer limit, using DFT-derived tight-binding models and using both efficient bulk and multi-terminal formalisms and techniques [2,3], I will first discuss the emergence of new forms of intrinsic spin Hall effect (SHE) that produce large and robust in-plane spin polarizations. Quantum transport calculations on realistic device geometries with disorder demonstrate large charge-to-spin interconversion efficiency with gate tunable spin Hall angle as large as θxy≈80%, and SHE figure of merit λs.θxy∼8-10 nm, largely superior to any known SHE material [4]. Besides, I will present our theoretical prediction of an unconventional canted quantum spin Hall phase in the monolayer Td-WTe2, which exhibits hitherto unknown features in other topological materials [5]. The low-symmetry of the structure induces a canted spin texture in the yz plane, dictating the spin polarization of topologically protected boundary states. Additionally, the spin Hall conductivity gets quantized (2e2/h) with a spin quantization axis parallel to the canting direction. Our theoretical predictions for the canted QSHE findings have just been confirmed experimentally [6], and we have also shown that a perpendicular electric field could tailor the canting angle, with a 90° coherent rotation [7]. I will finally discuss the role of entanglement between intraparticle degrees of freedom in spin transport and dynamical patterns of entanglement, as enabling novel platform for generating and manipulating quantum entanglement between internal and interparticle degrees of freedom [8]. [1] The 2020 Quantum Materials Roadmap, F. Giustino et al., J. Phys. Mater. 3 042006 (2020); [2] M. Vila et al., Phys. Rev. Lett. 124, 196602 (2020); [3] Z. Fan et al., Physics Reports 903, 1-69 (2021); [4] M. Vila et al., Phys. Rev. Research 3, 043230 (2021); [5] J.H. Garcia et al., Phys. Rev. Lett. 125 (25), 256603 (2020); [6] W. Zhao et al., Phys. Rev. X 11, 041034 (2021); [7] J.H. Garcia et al., submitted Phys Rev Lett.; [8] BG de Moraes et al., Physical Review B 102 (4), 041403 (2020).

Thursday 13 October 2022, 09:00 at LPTENS, Salle Jaurès, ENS Paris
( https://sites.google.com/view/parisiday-ens/home register at http://www.phys.ens.fr/spip.php?article5622 )
WORK-CONF (Workshop or Conference) hep-th
Two Days With Giorgio Parisi In Paris TBA

Friday 14 October 2022, 09:00 at LPTENS, Salle Jaurès, ENS Paris
( https://sites.google.com/view/parisiday-ens/home register at http://www.phys.ens.fr/spip.php?article5622 )
WORK-CONF (Workshop or Conference) hep-th
Two Days With Giorgio Parisi In Paris TBA

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