Krylov complexity has it all
Abstract
This paper establishes that Krylov complexity contains the entire information about the dynamics of a quantum operator, extending the list of equivalent quantities that can serve this purpose, such as the Lanczos coefficients, the return amplitude, and the spectral density. To demonstrate this equivalence, an explicit recursive algorithm is constructed to calculate Lanczos coefficients from the Taylor expansion of the Krylov complexity around t=0. Furthermore, the paper discusses the distinction between Krylov and spread complexity, clarifying why a similar recursive algorithm cannot exist for the latter without additional dynamical input. These results provide a ``proof of principle'' for using Krylov complexity as a complete characterization of operator evolution in quantum systems.
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BibTeX
@misc{muck2026krylov,
title = {{Krylov complexity has it all}},
author = {Wolfgang Mück},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2605.28681},
eprint = {2605.28681},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.28681},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Krylov complexity has it all
AU - Wolfgang Mück
PY - 2026
DA - 2026/09/10
PB - arXiv
DO - 10.48550/arxiv.2605.28681
UR - https://arxiv.org/abs/2605.28681
AB - This paper establishes that Krylov complexity contains the entire information about the dynamics of a quantum operator, extending the list of equivalent quantities that can serve this purpose, such as the Lanczos coefficients, the return amplitude, and the spectral density. To demonstrate this equivalence, an explicit recursive algorithm is constructed to calculate Lanczos coefficients from the Taylor expansion of the Krylov complexity around t=0. Furthermore, the paper discusses the distinction between Krylov and spread complexity, clarifying why a similar recursive algorithm cannot exist for the latter without additional dynamical input. These results provide a ``proof of principle'' for using Krylov complexity as a complete characterization of operator evolution in quantum systems.
ER -