• Séminaire nano-électronique quantique
• Personne à contacter : Loïc Herviou ()
• Lieu : Salle Rémy Lemaire K223, Institut Néel

Résumé : Quantum reservoir engineering leverages dissipative processes to achieve desired behavior, with applications ranging from entanglement generation to quantum error correction. Thereby, a structured environment thereby acts as an entropy sink for the system and no time-dependent control over the system is required. In this work, we focus on an active approach to reservoir engineering, where time-dependent control over a quantum system is used to manipulate its environment. In this case, the system may act as an entropy sink for the environment. We develop a theoretical description for active reservoir engineering that captures the dynamical interplay between system and environment, and provides an intuitive picture of how finite-size effects and system-environment correlations allow for manipulating the environment by repeated initialization of the quantum system. We illustrate our results with two examples: a superconducting qubit coupled to an environment of two-level systems and a semiconducting quantum dot coupled to nuclear spins. In both scenarios, we find qualitative agreement with previous experimental results. By providing a theoretical framework for active reservoir engineering, our work opens new avenues to control open quantum systems.

Liens :

• Séminaire théorie
• Personne à contacter : Adolfo Grushin ()
• Lieu : G421

Résumé : Topological phases of matter are distinguished by robust properties that are insensitive to perturbations. These include quantized responses, perfectly conducting interfaces, and exactly zero energy modes, with wide-ranging technological applications. Recent years saw the complete classification of topological band structures, revealing an abundance of topological crystalline insulators. Many questions about the robustness of these phases to disorder are, however, still open. We develop new theoretical and numerical methods based on local topological markers and effective momentum-space Hamiltonians to study topological phases in disordered systems. We introduce symmetry indicators for amorphous systems, and we also demonstrate that it is possible to construct a fully isotropic and inversion-symmetric three-dimensional medium where time-reversal symmetry is systematically broken. We propose an amorphous system with scalar time-reversal symmetry breaking, implemented by hopping through chiral magnetic clusters along the bonds. The average spatial symmetries alone protect a statistical topological insulator phase in this system, analogous to crystalline mirror Chern insulators. We also show the expected transport properties of a three-dimensional statistical topological insulator, which remains critical on the surface for odd values of the invariant.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Anna Minguzzi ()
• Lieu : Salle Roger Maynard G-421

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Adolfo Grushin ()
• Lieu : Salle Roger Maynard G-421

Résumé : Herbertsmithite is the leading candidate to host a quantum spin liquid -- a long sought state of matter featuring long-range quantum entanglement and fractionalised 'spinon' excitations. However, despite two decades' work, definitive evidence remains lacking. One complicating factor is that the material features significant disorder in the form of magnetic impurities. Here we utilise these impurities as 'witnesses' to probe the quantum spin liquid. Using spin noise spectroscopy to measure witness magnetization fluctuations, we find unusual 1/f noise develop below a cusp in DC magnetic susceptibility at 260mK. Ageing effects confirm witness spin glass formation. I will present a microscopic model of witness interactions mediated by a Z2 quantum spin liquid. Despite having only one free parameter, the model gives a quantitative match to all experiments, including a spin glass transition, the temperature dependence of the susceptibility, the temperature and frequency dependence of the noise spectrum, the Curie Weiss temperature, and the previously observed neutron scattering intensity as a function of momentum transfer.

Liens :

• Séminaire théorie
• Personne à contacter : Adolfo Grushin ()
• Lieu : Salle Roger Maynard G-421

Résumé : We introduce the time-dependent Quantum Geometric Tensor (tQGT) as a unified framework for characterizing the geometric properties of insulating systems within linear response theory. We demonstrate that the tQGT captures the zero-point motion of bound electrons and serves as a generating function for a family of generalized sum rules governing optical conductivity. We also discuss how quantum geometry modifies projected interactions and shapes the linear response in flat-band systems. Finally, we propose an alternative basis for representing interactions in topological bands, motivated by the structure of the projected density operator.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Léonie Canet ()
• Lieu : Salle Roger Maynard G-421

Liens :LPMMC

• Séminaire interne LPMMC
• Personne à contacter : Léonie Canet ()
• Lieu : Salle Roger Maynard G-421

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Salle Roger Maynard G-421

Liens :

• Séminaire LPMMC
• Personne à contacter : Anna Minguzzi ()
• Lieu : Salle Roger Maynard G-421

Liens :

• Séminaire QuantAlps
• Personne à contacter : Michele Filippone ()
• Lieu : PARAMS

Liens :