The center for Theoretical Physics (CPHT) at Ecole Polytechnique gathers research scientists working in diverse domains of fundamental and applied Physics. The overall coherence is assured by the corpus of common, transposable, mathematical and numerical methods.
CPHT is a joint research unit of CNRS and Ecole Polytechnique, and has a partnership with the Collège de France. His director is Jean-René Chazottes, Senior Researcher at CNRS.
CPHT is on the campus of Ecole Polytechnique, buildings 5 and 6. The reception offices are located in building 6 , offices 06.1046 and 06.1045.

Postal Address :
Ecole Polytechnique 
91128 Palaiseau cedex 

Secretary phone number : 01 69 33 42 01 (from abroad: +33 169 334 201)

Write an email to someone at CPHT :  :


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.






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.




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".

Superconducting qubits are one of the most promising platforms to implement quantum technologies. Quantum processors of tens of qubits are now available, and exciting applications with these intermediate size systems are in perspective. However, many algorithms, including all those with a proved quantum speed-up, require extremely low error rates. This will most likely require quantum error correction (QEC). Unfortunately, current QEC architectures require daunting overheads in physical qubits and control electronics. The goal of this research is to reduce this overhead, and our approach is based on two key ideas. First, we redundantly encode quantum information in Schrödinger cat states embedded in superconducting resonators. Second, we engineer non-linear dissipation to protect and manipulate this information.


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.

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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.




Le premier colloquium du CPHT de cette nouvelle série aura lieu mardi 19 novembre à 11h en salle des conférences Louis Michel

Mette Gaarde, Professeure à l'Université d'État de la Louisiane

"Making movies of ultrafast dynamics: tracking and controlling femtosecond absorption and emission processes"

Immense progress in the development of femtosecond and attosecond light sources means that scientists are now routinely directing movies of ultrafast electron and molecular dynamics as it is unfolding on its natural time scale. For example, intense femtosecond X-ray pulses from free-electron lasers can directly take pictures of molecular structural changes, and attosecond extreme ultraviolet (XUV) pulses have been used to time the photoelectric effect. I will start this talk with a brief overview of different types of dynamics that are of interest to the ultrafast community and how to probe them. Then I will discuss an example of opto-optical modulation: how to manipulate the femtosecond time-dependence of absorption and emission processes in gases, with an optical laser pulse, in order to control the temporal and spatial properties of an XUV pulse.



La Journée des Thèses a eu lieu au CPHT le vendredi 22 novembre 2019  dans la salle de conférence Louis Michel.

Format : 10 minutes/exposé + 5 minutes pour les questions

10h00 - 11h15

• [10h00 - 10h15] Nicolas DELPORTE Quantum field theory on random geometries

• [10h15 - 10h30] Jordan MOLES Concentration inequalities

• [10h30 - 10h45] James BOUST Rare-Earth-based hard magnetic materials

• [10h45 - 11h00] Thibaut COUDARCHET Vacuum stability in string theory

• [11h00 - 11h15] Alice MOUTENET Developing diagrammatic algorithms to tackle the quantum many-body problem in and out of equilibrium

11h15 - 11h30 : pause café

11h30 - 12h45

• [11h30 - 11h45] Julian LEGENDRE Topology in magnetically ordered Kagome systems

• [11h45 - 12h00] Jan SCHNEIDER Correlation spreading in long-range systems

• [12h00 - 12h15] David RIVERA Topological regularization of gravity

• [12h15 - 12h30] Nahuel BARRIOS Perturbative study of long-distance non-abelian gauge theories

• [12h30 - 12h45] Hepeng YAO One-dimesional ultracold bosons in quasiperiodic potential: localization and fractality

12h45 - 14h00 : pause déjeûner

14h00 -15h00

• [14h00 - 14h15] Sabine HARRIBEY Renormalization in tensor field theory and the melonic fixed point

• [14h15 - 14h30] Benjamin BACQ-LABREUIL Study of an unconventional phase in Na-doped Ca2CuO2Cl using Dynamical Mean Field Theory

• [14h30 - 14h45] Louis VILLA Correlation spreading and excitation spectra of quantum systems out-of-equilibrium

• [14h45 - 15h00] Grégoire VARILLON Non-modal hydrodynamic stability analysis of ablation flows relative to inertial confinement fusion

15h00 - 15h15 : pause café

15h15 - 15h30

Aurélien Canou : Soutien au calcul numérique au CPHT

15h30 - 16h30

• [15h30 - 15h45] Mufei LUO The role of laser bandwidth and random phase effects on the coupling in stimulated scattering instabilities in inhomogeneous plasma

• [15h45 - 16h00] William FOCILLON Structure du spin du proton et théorie de jauge

• [16h00 - 16h15] Balthazar DE VAULCHIER Induced gravity through compactification

• [16h15 - 16h30] Dung LE Light-cone wave function of onium in onium-nucleus scattering in different frames

16h30 : goûter et présentation des nouveaux membres du CPHT



IQUPS organises a new series of courses: on November 26 and  December 10, 12 and 17 (2019), two courses will take place in the same mornings from 9:15 to 12:30:

Quantum fluids of light by Jacqueline Bloch (C2N, Palaiseau) and Quentin Glorieux (LKB, Paris)
Open Quantum Systems: Foundations and Applications by Laurent Sanchez-Palencia (Centre de Physique Théorique, Institut Polytechnique de Paris, Palaiseau)

The courses, in English, will take place at the grand amphi in C2N (new site near IOGS and Polytechnique).

For PhD students: the courses are labelled "complément de formation initiale" by the doctoral schools EDPIF et EDOM.

To attend the courses, please register on-line or send a mail to

See more : here