Are we living in the Matrix? What quantum experiments reveal about the world and our powers in it, and what the future may hold.
le lundi 22 avril 2024 à 11:00
Séminaire QuantAlps
Personne à contacter : Michele Filippone ()
Lieu : Nevill Mott - D420 - 3rd Floor
Résumé : In the original Matrix movie, the bulk of the human population lives not in the real world but inside a computer simulation called the Matrix. They are unable to detect this situation, except for the fact that certain agents can transcend the normal rules of physics. In this talk, I will explain how this is eerily similar to the world we live in. Certain people (quantum physicists) can transcend the normal rules by using entangled particles to do things that "should be" impossible. This makes the world very puzzling place, even for quantum physicists. These “super-powers” are also central to the emerging field of quantum information technology. Finally, I will explain very recent work by myself and co-workers that ties all of this together in order to show that the world is even more puzzling than we had thought. Much like the latest Matrix movie.
Quantum phase transitions: microscopic scale and Planckian time
le mardi 07 mai 2024 à 14:00
Séminaire nano-électronique quantique
Personne à contacter : Jeremie Viennot ()
Lieu : Salle Rémy Lemaire K223, Institut Néel
Résumé : For more than thirty years, experimental analysis of quantum phase transitions (QPTs) has been
largely focused on finding critical exponents and universality classes of studied systems. This
approach emphasizes scale-invariance of QPTs and ignores the fact that system response also
depends on two non-universal length scales: microscopic “seeding” scale of the correlation
length and the dephasing length. Correcting this deficiency, we have developed a
phenomenological model of QPTs based on conjecture that the dephasing length is set by a
distance travelled by a system-specific semi-classical elementary excitation over the Planckian
time, and that the scaling function assumes the generic exponential form predicted
by the scaling theory of localization (the figure shows some examples). Using this model, we
have quantitatively explained QPTs in eighteen systems including: magnetic-field-driven QPT
in superconducting films, nanowires, La1.92Sr0.08CuO4 and Josephson junction chains; QPT in
Ising and Heisenberg spin chains, the Mott transition in 2d cold atomic gases and moiré
superlattices; and QPT between the states of quantum Hall and other topological insulators. The
model illuminates the universal microscopic nature of many-body gapless state of matter
emerging near QPTs. Surprisingly, the only system deviating from the trend is doped Si : P,
where metal-insulator transition is explained by the non-interaction version of the model. We
anticipate that shifting emphasis from critical exponents to the microscopic parameters of a
phase transition will be a fruitful approach for many systems beyond equilibrium condensed
matter physics.
Ref. :
[1] A. Rogachev, Microscopic scale of quantum phase transition: from doped semiconductors to
spin chains, cold gases and moiré superlattices, arXiv:2309.00749.
[2] A. Rogachev and K. Davenport, Microscopic scale of pair-breaking quantum phase
transitions in superconducting films, nanowires and La1.92Sr0.08CuO4, arXiv:2309.00747.
[3] A. Rogachev, Quantum phase transitions in quantum Hall and other topological systems: role
of the Planckian time, arXiv:2309.00747.
