• Accepted Paper

Information content of Krylov observables: A machine learning approach

Ritam Basu

Phys. Rev. D - Accepted 8 October, 2026

DOI: https://doi.org/10.1103/hqts-lp2n

Abstract

We employ machine learning techniques to estimate the amount of information contained in three Krylov-space observables: the spread complexity C(t), the discrete Wigner negativity N(t), and the normalized negativity χ(t)=N(t)/|S(t)|, where S(t) is the survival amplitude. We study thermofield-double evolutions on GUE, GOE and Poisson spectra, and on the integrable SL(2,R) Krylov chain of a two-dimensional CFT, primary with Lanczos coefficients bn=αn(n+2h−1). To introduce chaos we add a GUE random matrix to the integrable chain, H(ε)=HSL(2,R)+εR0WGUE, where R0 is its spectral half-width. Either C(t) or N(t) alone determines the thermofield temperature, with R2≃0.999. However, neither can reconstruct the fine structure of the spectral form factor. In the integrable sector all three observables carry the same information. When we turn on chaos an asymmetry appears: χ predicts C better than C predicts χ. This gap grows from +0.33 to +0.77, while the same gap for the raw negativity decays to zero. Thus we conclude the extra information comes from the survival amplitude and χ(t) carries it while C(t) can still be recovered from χ(t). We derive a lower bound on this gap, set by the fraction of the variance of χ that comes from S.

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