Séminaires du LPTMC

Salle de l'IMPMC (22-23, 4e étage, salle 401)

Modeling dynamical correlations in bilayer electronic materials

Two-dimensional electronic compounds, as well as systems composed of two or few such layers,
have recently been at the center of rapidly growing interest, for their remarkable tunability
and their wildly complex phase diagrams. They feature a wide range of properties
(correlated and topological insulators, superconductors, strange metals and more), which renders
them extremely interesting as a test bed for exotic electronic effects and, in perspective, for
applications to future electronic devices.
In this seminar, I will discuss some recent results of ours regarding two such systems, the
1T-1H TaS2 heterobilayer and Magic Angle Twisted Bilayer Graphene.
I will introduce the theoretical framework we employed to properly describe their electronic
correlations, based on Dynamical Mean-Field Theory and extension thereof, and discuss the
results of our simulations with regards to heavy fermion and local moment physics, ordering and
transport properties. I will provide comparisons with recent experimental results both from
Scanning Tunneling Microscopy and the new Quantum Twisting Microscope.
I will finally give some perspectives on the next steps of our analysis, with attention to
electron-phonon interaction, topology and superconductivity.

References
[1] Z.D. Song and B. A. Bernevig, Phys. Rev. Lett. 129, 047601 (2022)
[2] D. Wong et al, Nature 582, pages 198–202 (2020)
[3] J. Xiao et al, arXiv:2506.20738
[4] H. Kim et al, arXiv:2505.17200
[5] G.Rai et al, Phys. Rev. X 14, 031045 (2024)
[6] W. Ruan et al, Nat. Phys. 17, 1154 (2021)
[7] V. Vaňo et al, Nature 599, 582 (2021)
[8] L. Crippa et al. Nat. Commun. 15, 1357 (2024)

Salle 523, couloir 12-13, 5è étage

Majorana bound states in Kitaev chains coupled to photons

Embedding quantum materials into photonic cavities has emerged as a promising avenue for controlling properties of materials. The Kitaev chain - a prototype model for Majorana bound states (MBS) in topological superconductors - has attracted a lot of renewed interest. This is motivated by recent experimental realizations of a two-site Kitaev chain in an array of quantum dots connected by superconductors. The concept of ”poor man’s MBS” arising in such platforms was introduced back in 2012, with multiple theoretical works appearing in the past two years demonstrating new insights into the model. ”Poor man’s" MBS in a non-interacting two-site Kitaev chain emerge when the parameters of the Hamiltonian are fine-tuned to a sweet spot, such that the chemical potential is fixed to zero and the hopping equals the superconducting pairing. This is a very stringent condition. Moreover, the effect of particle interactions in quantum dots-based platforms is important as it leads to the hybridization between MBS and removes the sweet spot.

In this talk, I will discuss a new way to tune ”poor man’s" MBS with cavity embedding [1]. I will demonstrate that coupling to photons can be used to screen electron interactions allowing for reaching the sweet spot and realizing the isolated MBS. Moreover, I will show that cavity spectroscopy could be used to probe the ground state degeneracy between even and odd parity sectors. Next, I will extend the discussion to a Kitaev chain with N sites embedded in a cavity. I will demonstrate that the photon number and the photonic field quadratures peak at values of the chemical potential corresponding to parity switching points revealing a property of a finite-length Kitaev chain in the topological phase [2]. This later finding suggests that quantum optics experiments could be employed to detect topological features of the Kitaev chain embedded into a photonic cavity.

[1] Á. Gómez-León, M. Schirò, O. Dmytruk, Physical Review B 111 (15), 155410 (2025).

[2] V. F. Becerra, O. Dmytruk, arXiv:2506.06237.

Salle 523, couloir 12-13, 5è étage

Simulating quantum many-body systems

A significant part of the condensed matter community has been devoted to understanding and modeling strongly correlated quantum materials. To tackle the complexity of quantum many-body problems, a wide array of “classical” computational methods has been developed [1-3]. Paradigmatic models such as the Hubbard model (and its extensions) or the transverse-field Ising model—despite their apparent simplicity—have sparked extensive computational investigations in both equilibrium and nonequilibrium settings, and in various dimensions. In recent years, progress in algorithms and increasing classical computational power have led to a convergence of state-of-the-art methods, which now begin to agree within their overlapping regimes of applicability [4-6]. Yet, quantum systems exhibiting long-range entanglement at low temperatures remain especially challenging for classical numerical approaches. An alternative route is provided by synthetic quantum simulators: highly tunable experimental platforms governed by quantum mechanics, capable of faithfully implementing target Hamiltonians [7-9]. These include cold atoms in magneto-optical lattices and superconducting circuits. Among them, cold atom platforms stand out for their flexibility in realizing diverse systems and finely tuning microscopic interactions, achieving temperatures low enough to explore exotic phenomena such as unconventional superconductivity [10]. However, current quantum simulators still suffer from imperfections and noise [11-13], and many relevant quantum systems have yet to be mapped onto these platforms. In this seminar, I will present several classes of classical numerical methods designed to address quantum many-body problems in and out of equilibrium, outlining their advantages and limitations. I will also introduce several quantum simulation architectures and the challenges they face, and share ideas I have developed with collaborators to overcome these hurdles and enhance their capabilities.

[1-3] PhysRevB.43.5950, RevModPhys.68.13, RevModPhys.90.025003

[4-6] PhysRevX.13.011007, PhysRevX.11.041013, PhysRevX.11.011058

[7-9] PRXQuantum.2.017003, Nature Physics 8, 267–276, RevModPhys.80.885

[10] arXiv.2502.00095

[11-13] RevModPhys.87.637, PhysRevA.97.053803, J. Phys. B: At. Mol. Opt. Phys. 49 202001