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Thursday, 02 Mayl 2024

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- Video.mp4 (ca. 328 Mb)

15:15 – 16:15

"Origin of classicality in quantum spin systems"

Prof. Mikhail Katsnelson

(Radboud University Nijmegen)

Abstract:

Is quantum physics complete? In other words, does it describe all objects

in our Universe? If it is universally applicable why the most of the objects

in the world around us behave classically? This is the key issue of

hot discussions continuing already for almost a century, including the

famous discussions of Bohr and Einstein. A naive solution explaining

classicality of macro objects by their small de Broglie wavelength has obvious

shortcomings related to Schroedinger cat paradox or properties of systems

with chaotic motion. The most popular view is related to decoherence program

suggested long ago by Zeh, Zurek and other physicists and connecting

classicality of initially quantum systems with their openness.

I will discuss briefly the main idea of this approach and related concepts

such as pointer states and quantum Darwinism, as well as connection to the

measurement problem. To avoid unnecessary broadness and to keep closer

connection with the physical reality (whatever it means) I will illustrate these

concepts by examples of quantum magnets. I will especially discuss, first,

the relation between quantum singlet state of Heisenberg antiferromagnet and

classical Neel state and, second, emergence of topological protection for

quantum skyrmion state.

About the Speaker:

Mikhail Katsnelson is professor of theory of condensed matter at Radboud

University, Nijmegen (Netherlands). His main works are on the physics of

two-dimensional materials, magnetism, and strongly correlated systems.

His prizes includie Spinoza Prize (the highest scientific award in the Netherlands)

and Hamburg Prize for Theoretical Physics. He is elected member of

Royal Netherlands Academy of Artsand Sciences, Academia Europaea,

Uppsala Royal Scientific Society, and honorary doctor at Uppsala University.

He is currently Guest professor in the Wallenberg Initiative Materials Science

for Sustainability (WISE) hosted at Uppsala University.