Rok Žitko

Research councillor at the Jožef Stefan Institute
F1 — Department of Theoretical Physics

Office: Teslova 30, 1st floor, room 30
Institute: Jamova 39, SI-1001 Ljubljana, Slovenia

rok.zitko@ijs.si
ORCID · LinkedIn · Google Scholar · GitHub

I study quantum many-body effects in superconducting devices and strongly correlated materials, with a focus on quantum impurities, subgap states, and electronic transport. My work combines analytical approaches with numerical renormalization group and dynamical mean-field theory, and includes the development of open-source research software.

Recent work

Quasiparticle-resolved variational theory of Andreev spin qubits
Teodor Iličin, Rok Žitko
October 2026 · Preprint: arXiv:2610.08557 · PDF

A variational description of Andreev spin qubits in quantum-dot Josephson junctions, showing how virtual quasiparticles determine their Josephson couplings.

Research software

NRG Ljubljana

Numerical renormalization group solver for interacting quantum impurity models, including quantum dots and magnetic impurities in normal and superconducting hosts. It computes thermodynamic quantities, spectral functions, and transport coefficients, and can be used as an impurity solver in dynamical mean-field theory.

NRG Ljubljana documentation · Installation · Source code · Citation · Web app

SNEG

A Mathematica package for symbolic calculations with noncommuting operators in second quantization. It handles fermionic, bosonic, and spin algebras, including normal ordering, Wick contractions, symmetry-adapted bases, and operator matrix representations.

Installation · Source code · Citation

More software projects Hardware projects

Selected publications

Variational solution of the superconducting Anderson impurity model and the band-edge singularity phenomena

Phase diagram with Andreev-bound-state and Yu-Shiba-Rusinov regimes separated by a regime of singular behavior.

Teodor Iličin, Rok Žitko
SciPost Phys. 19, 006 (2025) · PDF

Correlation between two distant quasiparticles in separate superconducting islands mediated by a single spin

Schematic of a quantum-dot spin coupled to quasiparticle spins in two superconducting islands.

Juan Carlos Estrada Saldaña, Alexandros Vekris, Luka Pavešić, Rok Žitko, Kasper Grove-Rasmussen, Jesper Nygård
Nat. Commun. 15, 3465 (2024) · PDF

Direct manipulation of a superconducting spin qubit strongly coupled to a transmon qubit

Andreev spin-qubit Rabi oscillations versus microwave-pulse duration and amplitude, with Rabi frequency increasing with amplitude.

Marta Pita-Vidal, Arno Bargerbos, Rok Žitko, Lukas J. Splitthoff, Lukas Grünhaupt, Jaap J. Wesdorp, Yu Liu, Leo P. Kouwenhoven, Ramón Aguado, Bernard van Heck, Angela Kou, Christian Kraglund Andersen
Nat. Phys. 19, 1110 (2023) · PDF

Students and collaborators

I welcome enquiries about student projects and collaborations in quantum many-body physics, superconducting devices, and strongly correlated systems. Students can browse the student seminar topics. Please email rok.zitko@ijs.si with a brief description of your interests and background.