У оквиру традиционалног колоквијума Института за физику у Београду, у среду, 18. марта 2026. године у 12 часова у сали „Звонко Марић“ предавање под насловом:
Driven-dissipative spin systems in spintronics, magnonics and quantum computing
одржаће добитник награде „Марко Јарић“ за 2025. годину, проф. др Бранислав Николић (Универзитет у Делаверу, САД).
САЖЕТАК:
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).