Krylov complexity has it all

• URL: http://arxiv.org/abs/2605.28681v2
• Date: Wed, 03 Jun 2026 14:29:35 GMT
• Title: Krylov complexity has it all
• Abstract summary: This paper establishes that Krylov complexity contains the entire information about the dynamics of a quantum operator.<n>It provides a proof of principle'' for using Krylov complexity as a complete characterization of operator evolution in quantum systems.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• 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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