October 14 (Tuesday), 14:00, Room Louis Michel (CPHT)

Speaker: Sarath Prem (International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland)

Title: Distinguishing Majorana bound states from accidental zero-energy modes with a microwave cavity

Abstract: Detecting Majorana bound states (MBSs) in hybrid nanowires is challenging as their transport measurement signatures are often mimicked by trivial zero-energy Andreev bound states (ABSs) or zero-energy quasi-Majorana states (QMBSs) [1]. In this talk, I will present an alternative approach that relies on microwave absorption visibility that is extracted from parity-dependent cavity-nanowire susceptibility measurements [2]. We study a one-dimensional Rashba spin–orbit nanowire with an s-wave superconductor-covered proximitized region and an uncovered quantum dot region subjected to a magnetic field along the wire axis with spatially varying capacitive coupling to a single-mode cavity [2]. True MBSs yield a visibility extremum only when both Majorana modes at superconducting edges simultaneously couple to the cavity, even at resonant transitions from the zero-energy MBS state, exhibiting their nonlocal characteristics. In contrast, the zero-energy ABSs or QMBSs show a visibility extremum even when the cavity couples only locally to part of the nanowire. This distinction remains robust even with disorder or barriers. Owing to the recent experiments [3] of poor man’s Majorana (PMM) [4], we show that the visibility retains the nonlocal detection features and outline a scheme to initialize the PMM system to a particular parity [2]. Our results establish cavity-based visibility measurements as a nonlocal probe for MBS, offering a complementary tool for distinguishing MBSs from ABSs and QMBSs.

References:
[1] E. Prada, P. San-Jose, M. W. A. de Moor, A. Geresdi, E. J. H. Lee, J. Klinovaja, D. Loss, J. Nygård, R. Aguado, and L. P. Kouwenhoven, Nat Rev Phys 2, 575 (2020). [2] S. Prem, O. Dmytruk, and M. Trif, “Distinguishing Majorana bound states from accidental zero-energy modes with a microwave cavity,” (2025), arXiv:2509.13194. [3] T. Dvir, G. Wang, N. Van Loo, C.-X. Liu, G. P. Mazur, A. Bordin, S. L. D. Ten Haaf, J.-Y. Wang, D. Van Driel, F. Zatelli, X. Li, F. K. Malinowski, S. Gazibegovic, G. Badawy, E. P. A. M. Bakkers, M. Wimmer, and L. P. Kouwenhoven, Nature 614, 445 (2023). [4] M. Leijnse and K. Flensberg, Phys. Rev. B 86, 134528 (2012)./p>

Le séminaire des jeunes chercheurs du CPHT aura lieu le mercredi 1er octobre 2025 à 14h00 à la Salle de conférence Louis Michel avec deux présentations :

Arthur Klause, on An introduction to modern Wilsonian renormalization
The Wilsonian renormalization group equations provide a powerful framework for rigorously analyzing renormalizability and triviality in scalar field theories under various approximations. The perturbative renormalizability of the Euclidean scalar $\phi^4$ theory was established long ago, and more recently, its triviality has been proven in the mean-field approximation using non-perturbative methods. We will present the perturbative renormalizability and perturbative triviality of Euclidean scalar field theories with an interaction term of odd power greater than or equal to 6. In the Wilsonian renormalization group framework, such interaction terms naturally emerge in the effective Lagrangian when evolving from a bare phi^4 theory. We show that under natural renormalization conditions, the theory remains renormalizable and a bare perturbatively nontrivial theory. However, we demonstrate that certain alternative renormalization schemes can spoil the nontriviality that has been highlighted, underlining the renormalization scheme dependence of the theory's fate.

Victor Chabirand, The Wonderland of Carrollian physics: Exotic limit of the Poincaré group:
In this talk, we will first motivate the study of Carrollian physics. We will briefly introduce the holographic principle, which states that gravity is dual to a CFT living on the boundary of spacetime. Applied to asymptotically flat spacetimes, the dual theory should exhibit Carrollian symmetry. We will therefore study the Carroll group in an intrinsic manner. It can be viewed as the opposite limit to the Galilei group, with the speed of light taken to zero. In this strange wonderland, we will attempt to reconstruct classical mechanics, electromagnetism, statistical physics, and quantum mechanics. Our approach will be non-standard, even within the Carrollian community. This investigation will be fun, but it will also reveal important insights about ordinary Galilean physics. We will see that the Galilean limit is in fact a two-parameter limit, and not simply a low-speed limit. We will also see that there exist two Galilean electromagnetic theories, and we will establish the Lévy-Leblond equation describing a Galilean spin-1/2 particle.

Le séminaire sera suivi d'un goûter.

We are organizing a workshop on Electronic and Thermal Transport in Frontier Materials on October 2-3.
The talks will be held at Salle Louis Michel of CPHT on Oct 2 afternoon and Oct 3 morning.
The goal of the workshop is to bring together and exchange ideas between scientists working on thermoelectricity and transport phenomena in novel and interesting materials.

Workshop Schedule
Thursday, Oct 2 
14h00 - 14h45 Jonathan Alaria, From Bonds to Bands: Controlling Transport through Structural Motifs
14h45 - 15h30 Gael Grissonnanche, How can thermoelectric measurements probe quantum criticality?
15h30 - 15h45 Break
15h45 - 16h30 Andrje Pustogow, Flat Bands and Geometrical Frustration Boost Metallic Thermoelectrics
16h30 - 17h15 Jennifer Coulter, Advanced methods for first-principles Boltzmann transport predictions
17h15 - 17h35 Laura Agnarelli, Crystal Structure and Transport Properties in Ni7-xSnS2 and Ni10-xSn2S2
17h35 - 17h50 Break
17h50 - 18h35 Solveig Aamlid, Thermal properties of high entropy oxides
18h35 - 18h55 Anustup Mukherjee, Thermoelectric transport properties of hole-doped FeS2 and a lattice thermal conductivity comparison with RuS2

Friday, Oct 3
9h00 - 9h45 Silke Paschen, Weyl-Kondo semimetals
9h45 - 10h30 Krzysztof Wojciechowski, Composite Thermoelectric Materials with Attuned Electronic Structure and Mismatched Phonon Structure (AES-MPS)
10h30 - 10h45 Break
10h45 - 11h30 Jelena Sjakste, Coupled dynamics and transport of hot carriers and phonons in photoexcited semiconductors: theoretical approaches based on real-time propagation of carrier distributions
11h30 - 12h15 Jan-Willem Bos, Thermoelectric transport in half-Heusler and metal phosphide materials
12h15 - 13h00 Antoine Maignan, Thermopower, anomalous effects and magnetism in selected metallic oxides and metal-rich sulfides

Organisers
Alaska Subedi (CPHT)
Ramzy Daou (CRISMAT, Caen)
Laura Agnarelli (CRISMAT, Caen)
Sylvie Hebert (CRISMAT, Caen)

Dylan Bansard Tresse soutiendra publiquement ses travaux de thèse le lundi 29 septembre 2025 à 14h00  à l'Ecole polytechnique, CPHT, Amphi Louis Michel.

Titre :  "Return-time point processes in finite and infinite measure-preserving dynamical systems"
Directeur de thèse : Jean-René Chazottes

Anustup Mukherjee soutiendra publiquement ses travaux de thèse le vendredi 26 septembre 2025 à 11h00 à l'Ecole polytechnique, amphi Becquerel.
Titre : "First-Principles Analysis of Carrier Transport and Vibrational Properties in Pyrite-Structured Transition Metal Chalcogenides"y
Directeur de thèse : Alaska Subedi

Séminaire conjoint LSI+CPHT+PMC = M4S

vendredi 19 septembre à 10h

nouvelle salle de séminaire du PMC (anciennement salle Jean Mandel, au RDC de l'aile 5, près de l'aile 3).

Ioan Pop
(Karlsruhe Institute of Technology)

"Superconducting qubits and amplifiers resilient to tesla-scale magnetic fields"

Superconducting qubits with quantum non-demolition readout and active feedback can act as information engines to probe and control microscopic degrees of freedom, both engineered and environmental. However, the magnetic field bias poses a significant challenge for the operation of conventional qubits. We demonstrate a fluxonium qubit with a granular aluminum nanojunction (gralmonium) that maintains spectral stability and coherence above 1 T [arxiv.org/abs/2501.03661]. This robust performance enables exploration of spin environment dynamics and supports hybrid quantum architectures integrating superconducting qubits with spin systems.

Doctoral Training: SUCCESS-2025 - School on Ultraviolet and X-Ray Spectroscopies of Correlated and Topological Electron Systems

15 - 26 september 2025

Les Houches

Strong electron correlations and topology lie at the heart of quantum materials and their exotic states of matter. These are best understood by studying their electronic structure. This school, addressed to PhD students and young researchers, will introduce the recent experimental and theoretical developments in UV and X-ray spectroscopies, from their basic principles to their applications in the study of correlated materials.

The organizers:
Andrés F. Santander-Syro – Université Paris-Saclay (Orsay, France)
Silke Biermann – Institut Polytechnique de Paris (Palaiseau, France)
Patrick Le Fèvre – Université de Rennes (Rennes, France)
Ralph Claessen – Universität Würzburg (Germany)

More information can be found on the session's website.

Le séminaire des jeunes chercheurs du CPHT aura lieu le lundi 30 juin 2025 à 15h00 à la Salle de conférence Louis Michel avec deux présentations :

Valentine Maris from ENS de Lyon Introduction to noncommutative geometry and deformed Minkowski space-time :
Noncommutative geometry provides a representation of space-time in terms of associative algebras of operators. The final goal is to end up with a "quantum space-time" which should encode quantum gravity effects at an effective level. Recently, construction of such quantum space-times has been investigated and led to deformations of the usual Minkowski space-time.

Thomas Pochart QFT in AdS and its flat-space limit :
The Anti-de Sitter space is a fundamental concept in physics, arising naturally in GR and playing a key role in holography. We will discuss recent advances in quantum field theory for AdS spaces, and in particular its large radius limit, in which it is expected that we efficiently recover flat-space quantities.

Le séminaire sera suivi d'un goûter.