ELFT HÍRADÓ

[Szeminárium koordinátor <pusztai.tamas AT wigner.hun-ren.hu>]

SZFI SeminarMiklós WernerHUN-REN Wigner RCP SZFI Block entropy area based 
non-local fermionic mode optimization with gradient disentanglersTuesday, 10 
November 2026, 10:00, KFKI Campus, Bldg. 1, 2nd floor, Conference RoomIn this 
talk, I will discuss the use of tensor network approaches for systems of 
interacting fermions. Combining optimization by unitary rotations within the 
single-particle active space with the density matrix renormalization group 
(DMRG) yields an efficient low-rank ground-state algorithm. The first 
efficient implementations relied on local (nearest-neighbor) mode 
optimizations based on Rényi entropies, together with heuristic[1,2] or 
systematic[3,4] reorderings of the modes. For fermionic lattice models, it 
has also been shown that, despite the increased complexity of the 
Hamiltonian, the computational cost can be reduced by three to four orders of 
magnitude when optimized modes are used[2]. However, reorderings become 
destructive as the optimum is approached[3,4], since they are themselves 
single-particle unitaries (permutations) that change the cost function, 
namely the block-entropy area. This can lead to undamped oscillations that 
prevent convergence.Recently, we introduced a systematic non-local mode 
optimization algorithm based on the gradient of the block-entropy area[5]. 
From this gradient, we construct a long-range, non-interacting effective 
disentangler Hamiltonian. We then minimize the cost function by simulating 
the time-dependent Schrödinger equation driven by this Hamiltonian, using the 
time-dependent variational principle with projector splitting. Combining DMRG 
with this gradient-based entanglement minimization results in a superior 
low-rank iterative ground-state algorithm that requires no reorderings and is 
therefore free from the spurious oscillations of earlier approaches. We 
demonstrate the method on two-dimensional lattice models of interacting 
fermions and on the Fe4S4 cluster, and show its robustness and advantages 
over earlier protocols based on nearest-neighbor mode rotations and 
reorderings.[1] C. Krumnow, L. Veis, Ö. Legeza, and J. Eisert, Phys. Rev. 
Lett. 117, 210402  (2016).[2] A. Menczer, K. Kapás, MAW, Ö. Legeza, Phys. 
Rev. B 109, 195148 (2024).[3] G. Friesecke, MAW, K. Kapás, A. Menczer, Ö. 
Legeza, arXiv:2406.03449 (2024).[4] MAW, A. Menczer, Ö. Legeza 
(arXiv:2501.18263), published in Advances Quantum Chemistry 94, Hungarian 
Quantum Chemistry: Part B - Contemporary Research (2026). [5] MAW, G. 
Friesecke, A. Menczer, K. Kapás, Ö. Legeza, arXiv:2609.11811 
(2026). Minden érdeklődőt szívesen látunk! - Everyone is welcome to 
attend.Tamás Pusztaipusztai.tamas AT wigner.hun-ren.hu