The 16th CPHT Young Researchers Seminar will be held Monday 13th November at 15h00 in Jean Lascoux conference room.

Our two speakers are coming from out side our lab this time !!

Ismael Ahlouche (Mons University, Belgium): A geometric point of view on Wigner's classification

Nehal Mittal (Collège de France): Identifying topological phases: verification of bulk-edge correspondence

The seminar will be followed by a high tea.

The 15th CPHT Young Researchers Seminar will be held on November 9th, 2023 at 3:00 p.m. in the Louis Michel Conference Room with two presentations :

Pierre Wang: Analysis of the $\varphi^4_4$-theory with N components using the flow equations

Victor Dubois: Producing energy with nuclear reactions : focus on the fusion-fission hybrid reactor

The seminar will be followed by a high tea.

The 14th CPHT Young Researchers Seminar will be held on Friday the 20nd of October at 15h00 in Salle de conférence Louis Michel:

David Rivera Betancour : "Carrollian perspective of Ricci-flat spacetimes"

David Ramirez : "Chaos and hydrodynamics in 2D CFTs"

The seminar will be followed by a high tea.

Filippo Sottovia soutiendra publiquement ses travaux de thèse le 7 novembre 2023 à 14h00 au CPHT dans la salle de conférence Louis Michel

Titre : Revisiting the Landau criterion: a hydrodynamic and holographic approach to superfluid instabilities

Directeur de thèse: Blaise Goutéraux

La soutenance sera suivi du pot de thèse.

Majdouline Borji soutiendra publiquement ses travaux de thèse le 24 octobre 2023 à 14h00 au CPHT

Titre : Renormalization of QFTs which are not translation invariant

Directeur de thèse: Christoph Kopper

La soutenance sera suivi du pot de thèse dans la salle Jean Lascoux au CPHT.

Tuesday, March 12 at 14:30

at CPHT, Conference room Louis Michel

Eleanor Crane (MIT, USA)

Advantages of Digital Qubit-Boson Hardware for Quantum Simulation

Abstract: Finding a straightforward, scalable and universal framework for quantum simulation of strongly correlated fermions and bosons is important from material science to high-energy physics. Here, we develop hybrid qubit-oscillator operations for microwave cavities coupled to transmon qubits required for implementing dynamics of bosonic matter, fermionic matter, and Abelian gauge fields in (2+1)D. We then expand the method to ground state preparation and propose measurement of various long-range correlation functions required for the study of phase transitions. We implement numerical proof of principle experiments for a (1+1)D Z2 Bose Hubbard (BH) gauge theory and the U(1) Schwinger model. We include the main sources of hardware noise, which we mitigate through post-selection based on Gauss' law. This new approach motivates us to uncover the phase diagram of the Z2 BH model, relevant to the Higgs sector. We discover a new phase of matter which exhibits strong density fluctuations which we dub the `clump' phase. Finally, we perform a complexity analysis and find that for one Trotter step of these example models, qubit systems require higher gate counts than our proposal by three orders of magnitude. Our correspondingly higher circuit fidelities may help us to successfully capture the essential physics of these theories in the near-term.

Le CMAP, le CMLS et le CPHT organisent des journées thématiques dont l'audience visée est un large public de mathématicien-ne-s et de physicien-ne-s. La prochaine journée aura pour thème l'écologie, thème qui sera abordé sous différents points de vue par :

Ada Altieri (Laboratoire Matière et Systèmes Complexes, Université Paris Cité)
Guy Bunin (Physics departement, Technion)
Olivier Hénard (LMO, université Paris-Saclay)
Gaël Raoul (CMAP, CNRS, école polytechnique)

Cette journée aura lieu le 15 novembre 2023 de 10h30 à 16h15.

Plus d'informations sont disponibles à l'adresse suivante :
https://indico.math.cnrs.fr/e/themaEcologie15nov2023

Pour des raisons logistiques, l'inscription est gratuite mais obligatoire. Elle s'effectue à l'adresse suivante :
https://indico.math.cnrs.fr/event/10692/registrations/975/

En espérant vous y voir nombreux et nombreuses,
Pour l'organisation, Anne-Sophie de Suzzoni Jean-René Chazottes Anne de Bouard Cécile Huneau

Conférence grand public à l'occasion de la fête de la science

Samedi 14 octobre 2023 à 15h15 

Amphithéâtre Becquerel 

Tout est quantique !
par Laurent Sanchez-Palencia

La physique quantique a révolutionné notre compréhension du monde à l’échelle atomique et au-delà. Venez en découvrir les mystères, mais également comment elle a envahi les technologies du quotidien et ses promesses pour une nouvelle révolution technologique.

Plaquette de la fête de la science

Tuesday, October 17 at 14:00

at CPHT, Conference room Louis Michel

Ilya Kull (University of Vienna)

Lower bounds on ground-state energies of local Hamiltonians through the renormalization group

Abstract: "Quantum many-body systems present us with intractable optimization problems, e.g. finding the ground state of a many-body system. This problem is most often addressed through the variational ansatz approach, where physical insight can guide us in constructing the correct ansatz for a given system. Yet, variational methods can only provide us with a one sided estimate---an upper bound on the ground state energy. To certify a variational solution a lower bound is also required. Lower bounds can be obtained through relaxation methods, in which the optimization problem is simplified by relaxing some of the constraints that define the set of admissible optimization variables. Relaxation methods have been applied to many-body systems since the 50s and have also proven to be an essential tool in tackling various problems in quantum information theory and conformal field theory (the numerical bootstrap). Such methods, however, suffer from the drawback of exponential scaling of their complexity with the accuracy of the solution. In contrast, variational algorithms such as the density matrix renormalization group (DMRG), and other tensor-network algorithms which are based on the renormalization group idea, exhibit polynomial scaling.
In this talk I will describe how one can incorporate the power of the renormalization group approach into the relaxation framework to efficiently compute lower bounds. I will present the results we obtained with this method for translation-invariant spin chains where we observe a polynomial scaling of the complexity with the accuracy.

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.