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Physical Bridge for Open Quantum Systems: Krylov-Based Error Diagnostics for Quantum Computers

Daniel Süß

Published Mar 11, 2026• 0 citations
Publisher

Abstract

Extension of the Physical Bridge from closed to open quantum systems governed by Lindblad master equations. The proportionality C_meas(τ) ∝ C_op^open(τ) is proven to hold under arbitrary Markovian dissipation and verified numerically (Pearson r > 0.99) across three noise channels (dephasing, amplitude damping, depolarizing), two Hamiltonian families (Heisenberg, SYK₄), and dissipation strengths spanning two orders of magnitude. A key new result is that the Krylov framework provides qualitatively distinct signatures for coherent errors (Lanczos coefficient shifts) versus decoherence (autocorrelation envelope damping), enabling error-type discrimination for quantum computer benchmarking. Part 12 of the Krylov QKD research series.

DOI
10.5281/zenodo.18959826

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•Mar 31, 2026•0 citations
Extension of the Physical Bridge from closed to open quantum systems governed by Lindblad master equations. The proportionality C_meas(τ) ∝ C_op^open(τ) is proven to hold under arbitrary Markovian dissipation and verified numerically (Pearson r > 0.99) across three noise channels (dephasing, amplitude damping, depolarizing), two Hamiltonian families (Heisenberg, SYK₄), and dissipation strengths spanning two orders of magnitude. A key new result is that the Krylov framework provides qualitatively distinct signatures for coherent errors (Lanczos coefficient shifts) versus decoherence (autocorrelation envelope damping), enabling error-type discrimination for quantum computer benchmarking. Part 12 of the Krylov QKD research series.
This paper closes three theoretical gaps that remained open in the Krylov-based quantum channel authentication framework developed across Papers 1-8 of this series. Physical Bridge (Theorem 1): I derive a formal proof that the QBER autocorrelation is proportional to the operator autocorrelation, C_QBER(τ) = α(N) · C_op(τ), establishing the connection between Krylov theory and observable measurement statistics (numerically confirmed with Pearson r = 0.9997). Physical One-Way Function (Theorem 2): I prove that the Krylov fingerprint map constitutes a physical one-way function with three independent hardness sources: (I) unconditional information-theoretic exponential ill-conditioning of the inverse moment problem (κ_n ~ 32^n), (II) complexity-theoretic reduction to Hamiltonian learning, and (III) physical irreversibility of scrambling dynamics (t_rec ~ 10^765). Hardness source I is unconditional and provides post-quantum security. Universality (Theorem 3): I establish the universality of the detection framework through systematic numerical verification across 8 Hamiltonian families and 10 perturbation types, achieving 8/8 families and 10/10 perturbation types at the physically relevant distance d = 1. All three results are detector-agnostic: they characterize the Krylov framework itself, independent of the specific detection algorithm applied to the Lanczos coefficients. Paper 9 in the Krylov QKD series. See also: qkd-krylov-detector on GitHub.
A bstract We investigate Krylov complexity in open quantum systems using Lindblad master equations for bosonic bath models, with particular emphasis on the Caldeira-Leggett model. Krylov complexity is computed from the moments of the two-point function within the standard master equation framework. For the damped harmonic oscillator, the results reveal clear dissipative features in Krylov complexity. In the Caldeira-Leggett model, in the high-temperature limit, we find that Krylov complexity saturates in the full system and reproduces the expected dissipative behavior when the decoherence term is suppressed in the master equation. Conversely, when the dissipative term is suppressed, the contribution from decoherence exhibits the familiar oscillatory dynamics of the coherent system, along with additional novel features. However, Krylov complexity appears insensitive to the onset of decoherence, as no clear distinctive signature is observed. We attribute this to the fact that Krylov complexity is defined in the Krylov basis, which does not coincide with the conventional basis typically used to study decoherence.
Abstract Inspired by the universal operator growth hypothesis, we extend the formalism of Krylov construction in dissipative open quantum systems connected to a Markovian bath. Our construction is based upon the modification of the Liouvillian superoperator by the appropriate Lindbladian, thereby following the vectorized Lanczos algorithm and the Arnoldi iteration. This is well justified due to the incorporation of non-Hermitian effects due to the environment. We study the growth of Lanczos coefficients in the transverse field Ising model (integrable and chaotic limits) for boundary amplitude damping and bulk dephasing. Although the direct implementation of the Lanczos algorithm fails to give physically meaningful results, the Arnoldi iteration retains the generic nature of the integrability and chaos as well as the signature of non-Hermiticity through separate sets of coefficients (Arnoldi coefficients) even after including the dissipative environment. Our results suggest that the Arnoldi iteration is meaningful and more appropriate in dealing with open systems.
These notes are a short introduction to the mathematical theory of open quantum systems. They are meant to serve as an entry point into a broad research area which has applications across the quantum sciences dealing with systems subjected to external noise. The guiding idea is to let the key structures of the theory emerge from a concrete model. By working through the dissipative Jaynes-Cummings model the reader will dis- cover explicitly how irreversible dynamics arises from a unitary system-reservoir evolution. The notions of the continuous mode limit, correlation functions, spectral density appear in a natural manner and lead to the evolution equation of the open system in form of a master equation. This sets the stage for the more general analysis of completely positive, trace preserving (CPTP) maps and the study of quantum dynamical semigroups. We motivate and prove the Kraus representation theorem, the dilation theorem and the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) theorem. Working through the exercises (for which full solutions are supplied) will reinforce the ideas introduced in the main text.
Recently, the propagation of information through quantum many-body systems, developed to study quantum chaos, have found many applications from black holes to disordered spin systems. Among other quantitative tools, Krylov complexity has been explored as a diagnostic tool for information scrambling in quantum many-body systems. We introduce a universal limit to the growth of the Krylov complexity in dissipative open quantum systems by utilizing the uncertainty relation for non-Hermitian operators. We also present the analytical results of Krylov complexity for characteristic behavior of Lanczos coefficients in dissipative systems. The validity of these results is demonstrated by explicit study of transverse-field Ising model under dissipative effects.
This paper introduces an operational framework for quantifying reconstructability in open quantum systems under realistic conditions involving noise, measurement, and recovery processes. While decoherence theory explains the suppression of interference due to system–environment interactions, it does not directly address whether quantum states remain reconstructable in practice. To bridge this gap, this work proposes the Recoverability Index (RI), a scalar diagnostic that quantifies how close a system remains to reconstructable dynamics. The RI integrates three key components: recovery fidelity, entropy-like proxies of environmental information dispersal, and distinguishability of environmental records. Unlike traditional approaches that focus on coherence loss, this framework emphasizes reconstructability as an operational criterion, enabling a practical distinction between recoverable and effectively irreversible regimes. A simplified quantum error correction (QEC) scenario is used to demonstrate the applicability of the RI. The results show that the RI provides a transparent and interpretable metric for comparing noise conditions, evaluating recovery performance, and identifying boundaries of reconstructability. This work does not propose a new fundamental theory of quantum measurement. Instead, it offers a tool-oriented extension of the Entropy-Induced Collapse (EIC) framework, focusing on measurable quantities and practical diagnostics. The Recoverability Index serves as a bridge between conceptual descriptions of irreversibility and actionable evaluation in experimental and computational quantum systems. Keywords: quantum decoherence, quantum error correction, recoverability, irreversibility, open quantum systems, quantum information