[phys4phys] IPB Colloquium: Branislav Nikolić, Wednesday, 18 March 12:00

[Nenad Vukmirovic]

Dear colleagues,

You are cordially invited to the IPB COLLOQUIUM which will be held on Wednesday, 18 March 2026 at 12:00 in the “Zvonko Marić” lecture hall of the Institute of Physics Belgrade. The talk entitled

Driven-dissipative spin systems in spintronics, magnonics and quantum computing

will be given by Prof. Branislav Nikolić (University of Delaware, USA). The abstract of the talk:

The driven-dissipative many-body systems remain one of the most challenging unsolved problems of quantum physics. When “body” is spin, such as of electrons or of engineered ones like qubits, these many-body systems underlie spintronics, magnonics and quantum computing technologies. In this talk, I will first explain conditions [1] under which quantum spins interacting with a dissipative environment can transition toward classical dynamics governed by the celebrated Landau-Lifshitz-Gilbert (LLG) equation. The extended LLG equation for classical spin dynamics, which includes non-Markovian and spatially nonlocal damping of quantum origin, can be rigorously derived from Schwinger-Keldysh quantum field theory (SKFT) [2] by integrating out fermionic or bosonic bath and by neglecting quantum fluctuations of spin fields. Its application [3] to magnons explains recent experiments [4] where quantum sensing has measured 100-fold increase of magnon damping in yttrium iron garnet (one of the key materials in magnonics) due to metallic overlayer. It also explains [5] how to properly bring light into the LLG equation and predict optically excited magnons. In the case of fully quantum spin dynamics, by combining SKFT with two-particle irreducible effective (2PI) action formalism and 1/N expansion, both of which have been developed originally in elementary particle physics, we describe [6] time evolution of spin in archetypical open quantum system⸺the spin-boson model (that is also of great importance for understanding decoherence of idle superconducting qubits). Despite only a class of Feynman diagrams being resummed to infinite order by 2PI, where those diagrams are generated by expansion in 1/N (N in the number of Schwinger bosons to which spin is mapped) instead of expansion in the system-bath coupling, our SKFT can track numerically exact non-Markovian simulations from tensor networks (TN) methods. It also provides access to longer times and higher spatial dimensions where TN fail due to the emergence of “entanglement barrier.” These newly developed methods make it possible to understand, for the first time, fate of entanglement in open quantum spin liquids [7].

References
[1] F. Garcia-Gaitan and B. K. Nikolić, Phys. Rev. B 109, L180408 (2024).
[2] F. Reyes-Osorio and B. K. Nikolić, Phys. Rev. B 109, 024413 (2024).
[3] F. Reyes-Osorio and B. K. Nikolić, Phys. Rev. B 110, 214432 (2024).
[4] I. Bertelli et. al., Adv. Quantum Technol. 4, 2100094 (2021).
[5] F. Reyes-Osorio and B. K. Nikolić, Phys. Rev. Lett. 135, 246701 (2025).
[6] F. Reyes-Osorio, F. Garcia-Gaitan, D. J. Strachan, P. Plecháč, S. R. Clark, and B. K. Nikolić, Rep. Prog. Phys. 89, 018002 (2026).
[7] F. Garcia-Gaitan and B. K. Nikolić, https://arxiv.org/abs/2510.02256 (2025).

Branislav K. Nikolić is a Full Professor of Physics at the University of Delaware and a Senior Visiting Scientist at RIKEN in Japan. He received his Ph.D. in theoretical condensed matter physics from Stony Brook University, and a B.Sc. degree from the University of Belgrade, Serbia. He was visiting Professor at the University of Regensburg, National Taiwan University, Centre de Physique Théorique de Grenoble-Alpes and Beijing Normal University. His research focuses on nonequilibrium quantum many-body and field theory, computational quantum transport, multiscale quantum-classical approaches, and high-performance scientific computing, including applications to technologically relevant problems in spintronics, magnonics, quantum information, nanoelectronics, thermoelectrics and nano-bio interface.

Best regards,
Nenad Vukmirović

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Dr Nenad Vukmirović
Research Professor
Institute of Physics Belgrade
Pregrevica 118, 11080 Belgrade, Serbia
URL: http://www.scl.rs/nenad