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Krylov complexity is not a measure of distance between states or operators

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arxiv 2311.04093 v2 pith:BYDKWTTX submitted 2023-11-07 hep-th quant-ph

classification hep-thquant-ph
keywords complexitykrylovdistancemeasurestatescannotcircuitcompatible
verification ladder T0 review T1 audit T2 compute T3 formal
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We ask whether Krylov complexity is mutually compatible with the circuit and Nielsen definitions of complexity. We show that the Krylov complexities between three states fail to satisfy the triangle inequality and so cannot be a measure of distance: there is no possible metric for which Krylov complexity is the length of the shortest path to the target state or operator. We show this explicitly in the simplest example, a single qubit, and in general.

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Cited by 3 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. (A)Symmetric Complexity and the Quantum Mpemba Effect

    hep-th 2025-09 conditional novelty 6.0 of 10

    A new decomposition of Krylov complexity into projected symmetric and asymmetric parts diagnoses the quantum Mpemba effect, but its claimed t=0 predictor is computationally equivalent to time evolution.

  2. CFT Complexity and Penalty Factors

    hep-th 2025-07 conditional novelty 6.0 of 10

    A submersion-based method turns weighted generator costs into state-complexity metrics for CFTs, giving analytic formulas in simple limits and constraints on which weight choices are viable.

  3. Quasinormal modes and complexity in saddle-dominated SU(N) spin systems

    hep-th 2025-06 conditional novelty 5.0 of 10

    A family of SU(2) and SU(3) Lipkin-Meshkov-Glick-type Hamiltonians reproduces de Sitter quasinormal-mode densities of states, and late-time probes reveal integrability beneath saddle-dominated scrambling.

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