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 :  :



Pauline Besserve will defend her thesis on Friday, October 6th in Collège de France (11 place Marcelin Berthelot, 75005 Paris.
The defense will take place in room 4 at 2pm and will be followed by a pot in room 8.

Title: Hybrid quantum-classical algorithms for the quantum many-body problem

Advisors: Michel Ferrero (Centre de Physique Théorique, Collège de France) and Thomas Ayral (Eviden Quantum Laboratory).

The thesis explores the quantum-classical implementation of the celebrated Dynamical Mean-Field Theory to study strong electronic correlations in materials. These exhibit rich phases diagrams, spanning - among others - metallic, insulating, high-Tc superconducting behaviours according to external parameters, but remain notoriously difficult to tackle due to the exponential scaling of computational resources their description involves. Quantum computers are widely hailed as promising devices to ease the bottleneck of DMFT and the first, imperfect prototypes of such devices are now becoming available. The thesis explores the use of such imperfect devices concomitantly with that of classical computational power for DMFT. It addresses both of the impediments to a quantum-classical implementation of DMFT on current devices, namely low coherence time and low qubit count, by setting forth an improved variational state preparation scheme and using hardware noise as a resource to alleviate errors inherent to the low qubit count.



The 13th CPHT Young Researchers Seminar will be held on Friday the 22nd of September at 15h00 in Salle de conférence Louis Michel: 

Erik Linnér : "A theoretical description of competing instabilities in strongly correlated fermionic systems" 

Matthieu Vilatte : "Probing the asymptotic structure of gravity"

Adrien Loty : "Does string theory saturate unitarity bounds?"

The seminar will be followed by a high tea.



Colloquium Friedmann 28-9-2023 17:00 Amphi Faure

Slava Mukhanov (Ludwig-Maximilians-Universität München)
How predictive are cosmological theories ?

Affiche Colloquium

Biséminaire Friedmann CPHT-LLR  29-9-2023 salle de conférences du LLR (aile 5 - centre)

Oleg Lebedev (University of Helsinki)
Gravity, dark matter and its detection

Slava Mukhanov (Ludwig-Maximilians-Universität München)
False vacuum decay: thick wall approximation

Affiche Biséminaire




Tuesday, September 19 at 14:00

at CPHT, Conference room Louis Michel

Hareram Swain (IIT Madras)

A semi-holographic approach to strange metallic behaviour

Abstract: "Strange metals" exhibit an anomalous temperature dependence of the low temperature resistivity. This suggests the absence of electron quasiparticles which are the elementary excitations of the Fermi sea. This property is at odds with conventional Fermi liquids, justifying the “strangeness” of this phase. The measurement of the spectral function via ARPES has given us key insights into the nature of elementary constituents in strongly correlated electronic systems that do not admit quasiparticle description, and also demonstrate a rich variety of novel superconducting, metal, and insulating phases. The holographic approach, though allows one to dispense with the notion of quasiparticles, at the same time, this makes it difficult to understand what are the effective microscopic degrees of freedom of the system. In my talk, I will explain how we construct a semi-holographic description for such behaviours. Based on the key insights provided by Faulkner and Polchinski, we propose an effective theory in which the electron of a two-dimensional band hybridizes with a fermionic operator of a critical holographic sector, while also interacting with other bands that preserve quasiparticle characteristics. Besides the scaling dimension $\nu$ of the fermionic operator in the holographic sector, the effective theory has two dimensionless couplings α and γ determining the holographic and Fermi-liquid-type contributions to the self-energy respectively. In the case of DC conductivity that irrespective of the choice of the holographic critical sector, there exists a ratio of the effective couplings for which we obtain linear-in-T resistivity for a wide range of temperatures. This scaling persists to arbitrarily low temperatures when $\nu$ approaches unity in which limit we obtain a marginal Fermi liquid with a specific temperature dependence of the self-energy. Interestingly, we explain the origin of the linear-in-T resistivity and strange metallic behavior as a consequence of the emergence of a universal form of the spectral function which is independent of the model parameters when the ratio of the two couplings takes optimal values determined only by the critical exponent. This universal form fits well with photoemission data of copper oxide samples for under/optimal/over-doping with a fixed exponent over a wide range of temperatures. We further obtain a refined Planckian dissipation scenario in which the scattering time τ=f*h_bar/(k_B*T), with f being O(1) at strong coupling, but O(10) at weak coupling.



Ephraim Bernhardt will publicly defend his thesis work on September 18, 2023 at 10:30 a.m. at the CPHT in the Louis Michel conference room.

Title: Topology and disorder effects in interacting and open quantum spin systems and analogues

Advisor: Karyn Le Hur



Alberto Rosso, Directeur de recherche au CNRS, LPTMS, Université Paris-Saclay (Rapporteur)
Thomas Schmidt, Professeur, Université du Luxembourg (Rapporteur)
Cristiano Ciuti, Professeur, MPQ, Université Paris-Cité (Examinateur)
Michel Ferrero, Chargé de recherche au CNRS, CPHT, École Polytechnique (Examinateur)
Loic Henriet, Chief Technology Officer, PASQAL (Examinateur)
Peter P. Orth, Professeur, Universität des Saarlandes (Examinateur)
Matteo Rizzi, Professeur, Universität zu Köln, (Examinateur)
Karyn Le Hur, Directrice de recherche au CNRS, CPHT, École Polytechnique (Directrice de thèse)
Cyril Elouard, Junior Professor, LPCT, Université de Lorraine (Invité)

The defense will be followed by a reception in the Jean Lascoux room at the CPHT.

After the reception, there will be a workshop on « Quantum many-body physics - new directions and modern applications ».



Chair: Karyn Le Hur, thesis supervisor, CNRS, CPHT, École Polytechnique

- 14h15 - 14h45 Matteo Rizzi (Universität zu Köln): Phase Diagram Detection via Gaussian Fitting of Number Probability Distribution

- 14h45 - 15h15 Thomas Schmidt (Université du Luxembourg) Topology and semiclassical transport in interacting electron system

-15h15 - 15h45 Peter P. Orth (Universität des Saarlandes) Nonlinear interrogation of quantum materials: why higher order response tells you more

- 15h45 - 16h15 Cyril Elouard (LPCT, Université de Lorraine) Extending the laws of thermodynamics for arbitrary autonomous quantum systems

16h15 - 16h30 Café et en-cas

- 16h30 - 17h00 Cristiano Ciuti (MPQ, Université Paris-Cité) New quantum many-body effects in high-impedance multi-mode circuit QED

- 17h00 - 17h30 Loic Henriet (Pasqal) tba

- 17h30 - 18h00 Alberto Rosso (CNRS, LPTMS, Université Paris-Saclay) tba

- 18h00 - 18h30 Michel Ferrero (CNRS, CPHT, École Polytechnique) tba



Tuesday, September 12 at 14:00

at CPHT, Conference room Louis Michel

Naoya Iwahara (Chiba University, Japan)

Dynamic Jahn-Teller effect in cubic spin-orbit Mott insulators

Abstract: The synergistic interplay of different interactions in materials leads to the emergence of novel quantum phenomena. Spin-orbit and vibronic couplings usually counteract each other; however, in cubic 4d/5d double perovskites they can coexist and give rise to spin-orbit-lattice entanglement (dynamic Jahn-Teller effect) on the metal sites. The correlation of these entangled states induced by intersite interactions has not been assessed so far. In the seminar, I will first show that the dynamic Jahn-Teller effect develops in iridium compounds based on the analysis of the resonant inelastic x-ray scattering spectra [1]. Then, I will talk about the ordering of the entangled states in a series of cubic 5d1 double perovskites [2]. The magnetically ordered states in these systems coexist with a vibronic order characterized by the ordering of vibronic quadrupole moments on sites. This treatment allows for the rationalization of a number of unexplained features of experimentally investigated phases.

[1] N. Iwahara and W. Furukawa, Phys. Rev. B 108, 075136 (2023).
[2] N. Iwahara and L. F. Chibotaru, Phys. Rev. B 107, L220404 (2023).




Olesia DMYTRUK, CNRS research fellow with the Center for Theoretical Physics at École Polytechnique, was awarded an ERC Starting Grant.

She receives the ERC support for her project "Quantum light-controlled topological phases of matter".

Controlling properties of materials with light is a novel research direction of condensed matter physics. Topological materials play a particularly important role in this direction due to their robustness and their possible applications in quantum technologies. The aim of the Q-Light-Topo project led by Olesia Dmytruk is to propose a protocol for engineering topological phases of matter with light. To achieve this goal, solid-state systems such as nanowires and two-dimensional materials coupled to cavity photons will be considered. Olesia Dmytruk's project will explore how to control topological phase transitions in various topological materials strongly coupled to light, and also study properties of hybrid polaritonic light-matter excitations arising in such systems.


Renaud Garioud will publicly defend his thesis work on Tuesday 4th July. The defense will be held at 3p.m. in room 2 of Collège de France (Collège de France, 11 Pl. Marcelin Berthelot, 75231 Paris)

Title: When perturbation theory becomes non-perturbative : application to strongly correlated systems

Advisor: Michel Ferrero

Abstract : Strongly correlated materials reveal remarkable physical phenomena at low temperatures. Depending on external parameters, they exhibit extremely different electronic phases, ranging from insulating magnetic orders to strong superconductivity with infinite electrical conductivity. The richness of these physical phenomena takes its roots in the strong interactions that impact heavily the behaviour of electrons. To accurately describe these properties, one must solve the quantum many-body problem of interacting particles. In this thesis, we focus on the development of new algorithms to address strongly interacting fermionic systems.

By considering electronic interactions as a perturbation to the non-interacting system, we focus on computing efficiently, and up to high orders, the perturbation series, which can be expressed as sums of Feynman diagrams. We present the CDet (Connected Determinants) state-of-the-art algorithm which allows us to reach high perturbation orders. We overcome one of the main limitations of perturbation theory by introducing a novel chemical potential shift that breaks a symmetry. We show that this approach allows us to describe perturbatively the physics of ordered phases in the thermodynamic limit. We apply this new algorithm to the cubic half-filled Hubbard model and provide a quantitative description of the Néel order both near the phase transition and at low temperature up to the high coupling regime. This study enables us to detail the limitations to our method and to present the numerical tools that ensure an efficient implementation of the CDet algorithm and an accurate resummation of the resulting perturbative series. The attractive counterpart of this model shows a superconducting phase that can also be described by adapting our symmetry-breaking approach.


We are happy to announce the seminar entitled

"Control of Auto-Resonant Beat-Wave Excitation of Plasma Waves."
given by our former group member
Dr. Mufei Luo
(Chalmers University of Technology, Göteborg, Sweden)

Thursday 29th of June 2023 , 15 h
Salle Louis Michel of CPHT, building 06