Timelike Entanglement Signatures of Ergodicity and Spectral Chaos

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Main Authors: Das, Rathindra Nath, Kundu, Arnab, Sarkar, Nemai Chandra
Format: Preprint
Published: 2026
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author Das, Rathindra Nath
Kundu, Arnab
Sarkar, Nemai Chandra
author_facet Das, Rathindra Nath
Kundu, Arnab
Sarkar, Nemai Chandra
contents We investigate timelike entanglement measures derived from the spacetime density kernel in the Rosenzweig-Porter model and show that they sharply diagnose both eigenvector ergodicity and spectral chaos. For several Hilbert-space bipartitions, we compute the second Tsallis entropy, the entanglement imagitivity that quantifies non-Hermiticity, and Schatten-norm diagnostics of the kernel. The imagitivity and Frobenius norm exhibit rapid growth and high late-time plateaus in the ergodic regime, are suppressed in the localized regime, and show intermediate behavior in the fractal phase. The real part of the second Tsallis entropy displays a spectral form factor-like dip-ramp-plateau throughout the chaotic window and a suppressed ramp in the localized regime. We further introduce a kernel negativity, defined as the negative spectral weight of the Hermitian part of the kernel. This negativity equals the trace-norm distance to the set of positive semidefinite operators and the maximal witnessable negative quasiprobability, and its time-averaged value decreases across the ergodic-fractal-localized crossover in close correspondence with the fractal dimension.
format Preprint
id arxiv_https___arxiv_org_abs_2601_19981
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Timelike Entanglement Signatures of Ergodicity and Spectral Chaos
Das, Rathindra Nath
Kundu, Arnab
Sarkar, Nemai Chandra
High Energy Physics - Theory
Statistical Mechanics
Quantum Physics
We investigate timelike entanglement measures derived from the spacetime density kernel in the Rosenzweig-Porter model and show that they sharply diagnose both eigenvector ergodicity and spectral chaos. For several Hilbert-space bipartitions, we compute the second Tsallis entropy, the entanglement imagitivity that quantifies non-Hermiticity, and Schatten-norm diagnostics of the kernel. The imagitivity and Frobenius norm exhibit rapid growth and high late-time plateaus in the ergodic regime, are suppressed in the localized regime, and show intermediate behavior in the fractal phase. The real part of the second Tsallis entropy displays a spectral form factor-like dip-ramp-plateau throughout the chaotic window and a suppressed ramp in the localized regime. We further introduce a kernel negativity, defined as the negative spectral weight of the Hermitian part of the kernel. This negativity equals the trace-norm distance to the set of positive semidefinite operators and the maximal witnessable negative quasiprobability, and its time-averaged value decreases across the ergodic-fractal-localized crossover in close correspondence with the fractal dimension.
title Timelike Entanglement Signatures of Ergodicity and Spectral Chaos
topic High Energy Physics - Theory
Statistical Mechanics
Quantum Physics
url https://arxiv.org/abs/2601.19981