CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel

Giuseppe Policastro (ENS)

Title: Quantum complexity and holography

Abstract: I will discuss the motivations for introducing the notion of quantum complexity in physics, coming from the issues related to the information loss paradox in black holes. I will introduce the definition of complexity, the different proposals for its holographic computation, its inherent ambiguity, then present the computation for the case of a boundary/defect CFT.

Ridge, NY, 26 February 2020 — The American Physical Society (APS) has selected 147 Outstanding Referees for 2020 that have demonstrated exceptional work in the assessment of manuscripts published in the Physical Review journals. A full list of the Outstanding Referees is available online at http://journals.aps.org/OutstandingReferees.

The Summer School will take place from July 7 to July 17 2020 at the Institut d'Etudes Scientifiques de Cargèse, located on the west cost of the beautiful Corsica island, nearby the city of Ajaccio.

The purpose of this Summer School is to train the next generation of young researchers in the field of quantum simulation and, more generally, quantum technologies. Grouping together a diverse community as well as young and leading senior researchers, we expect a stimulating cross-fertilization of ideas, methods, and approaches, able to further develop this fields beyond the present frontiers.

Information about the Summer School, including a list of speakers and application forms can be found on the website: 
https://quantsim2020.sciencesconf.org

Important dates
Opening of applications: Mon, 24 Feb 2020
Deadline for application: Fri, 20 March 2020
Notification of acceptance: Mid-April
Deadline for registration: Mon, 15 May 2020

Organizers 
Thierry Giamarchi, Giacomo Roati, and Laurent Sanchez-Palencia

PhD student

Research group: Particle Physics

Thesis: "Proton spin structure and gauge symmetry"
Advisor: Cédric Lorcé

Keywords: Quantum Chromodynamics, Spin and Orbital Angular Momentum, Spectator Diquark Model.

Publication

Amor-Quiroz DA, Burkardt M, Focillon W, Lorcé C.
Potential linear and angular momentum in the scalar diquark model.
European Physical Journal C. 2021;81(7):589.
DOI: 10.1140/epjc/s10052-021-09345-9. 

Amor-Quiroz DA, Burkardt M, Focillon W, Lorcé C.
Study of the potential transverse momentum and potential angular momentum within the scalar diquark model.
Presented at the Workshop of QCD and Forward Physics at the EIC, the LHC, and Cosmic Ray Physics in Guanajuato, Mexico, November 18-21 2019.
arXiv:200608490

Silke Biermann, Présidente du Département de Physique à l'Ecole Polytechnique, Professeur à l'Ecole Polytechnique et chercheuse au Centre de Physique Théorique, s'est vue décerner la médaille d'argent du CNRS pour ses travaux développant des approches de calculs de structures électroniques pour les matériaux corrélés à partir de premiers principes.

La médaille d'argent distingue des chercheurs et des chercheuses pour l'originalité, la qualité et l'importance de leurs travaux, reconnus sur le plan national et international.

THURSDAY 13 FEBRUARY, 2 p.m.  SALLE LOUIS MICHEL

BALT VAN REES

QANTUM FIELD THEORY in ANTI-DE SITTER and the S-MATRIX

Abstract:
We discuss results obtained by considering gapped QFTs in a fixed Anti-de Sitter background. Much like in the AdS/CFT correspondence, we can naturally define
'boundary' observables that exhibit conformal invariance in one dimension less. These observables can be analyzed using conformal bootstrap techniques which results in new non-perturbative bounds on the strength of the coupling constants in a general QFT. When we send the AdS curvature to zero the boundary observables should morph into the S-matrix of the flat-space QFT. We will discuss the different ways in which this connection can be made explicit, and how it might end up teaching us new lessons about the non-perturbative structure of scattering amplitudes.

THURSDAY 13 FEBRUARY, 3.15 p.m.    SALLE LOUIS MICHEL

JÜRG FRÖHLICH

THE FOURTH PILLAR which QUANTUM MECHANICS RESTS UPON

Abstract:
Traditionally, the three concepts of states, observables and unitary evolution form the pillars Quantum Mechanics is built upon. It is well known that they do not suffice to solve, for example, the so-called measurement problem.
In this talk I will describe a fourth fundamental concept, proposed only recently, namely the "Principle of Diminishing Potentialities". I will then show how it enables one to come up with a precise notion of "events" in Quantum Mechanics and with a new understanding of the time evolution of states of isolated systems.
 As results, the "measurement problem" and the unitarity- or information paradox disappear, and a "Quantum Mechanics without Observers" emerges. 

The next CPHT colloquium will take place on Thursday, February 6 at 2 pm in the Louis Michel conference room.

The speaker will be Zaki Leghtas, and his topic will be quantum information.

"Quantum computing with Schrödinger cat states".

Le processus de définition de la stratégie européenne en physique des particules est en son cours. Après la réunion de Grenade, le « Physics Briefing Book » a été publié en septembre, et depuis le groupe restreint sur la stratégie prépare la session de rédaction de Bad Honnef (20-24 janvier 2020) qui doit déboucher sur des recommandations qui seront données au Conseil du CERN.

Plusieurs scénarios de futurs collisionneurs sont discutés dans ce cadre-là. Nous vous proposons d'échanger ensemble à ce sujet, le lundi 13 janvier de 14h à 17h dans l'amphi Charpak du LPNHE. Il s'agira notamment de présenter les scénarios considérés et de discuter d'une position commune française à défendre à Bad Honnef.

Inscription (gratuite mais indispensable) sur https://indico.in2p3.fr/event/20221/

Divers documents d’information sont disponibles aux liens suivants:

http://arxiv.org/abs/1912.11871

https://arxiv.org/abs/1912.13466

http://cds.cern.ch/record/2705370

PhD defense on December 17 at 2 pm in salle Louis Michel, CPHT, Ecole Polytechnique

Julien Despres
(Group Condensed Matter)

"Correlation spreading in quantum lattice models with variable-range interactions"

In this thesis, we have investigated the spreading of quantum correlations in isolated lattice models with short- or long-range interactions driven far from equilibrium via sudden global quenches. A main motivation for this research topic was to shed new light on the conflicting results in the literature concerning the scaling law of the correlation edge, its lack of universality and the incompleteness of the existing physical pictures to fully characterize the propagation of quantum correlations. To do so, we have presented a general theoretical approach relying on a quasiparticle theory. The latter has permitted to unveil a generic expression for the equal-time connected correlation functions valid both for short-range and long-range interacting particle and spin lattice models on a hypercubic lattice. Relying on stationary phase arguments, we have shown that its causality cone displays a universal twofold structure consisting of a correlation edge and a series of local extrema defining the outer and inner structure of the space-time correlations. For short-range interactions, the motion of each structure is ballistic and the associated spreading velocities are related to the group and phase velocites of the quasiparticle dispersion relation of the post-quench Hamiltonian. For long-range interactions of the form 1/|R|^{\alpha}, the correlation spreading is substantially different due to a possible divergence of group velocity when tuning the power-law exponent \alpha. For a divergent group velocity, ie. the quasi-local regime, we have presented evidence of a universal algebraic structure for the causality cone. While, the correlation edge motion has been found to be always slower than ballistic, the local extrema propagate faster than ballistically and ballistically for gapless and gapped quantum systems respectively. For the local regime implying a well-defined group velocity, we have recovered similar scaling laws and spreading velocities than the short-range case for the causality cone of correlations. The previous theoretical predictions have been verified numerically using tensor network techniques within the case study of the short-range Bose-Hubbard chain and the long-range s=1/2 XY and transverse Ising chains.