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Krylov complexity measures the spread of an evolved state in a natural basis, induced by the generator of the dynamics and the initial state. Here, we study the spread in Hilbert space of the state of an Ising chain subject to a…

Quantum Physics · Physics 2025-07-08 E. Medina-Guerra , I. V. Gornyi , Yuval Gefen

Krylov complexity is a novel measure of operator complexity that exhibits universal behavior and bounds a large class of other measures. In this letter, we generalize Krylov complexity from a closed system to an open system coupled to a…

Strongly Correlated Electrons · Physics 2023-08-11 Chang Liu , Haifeng Tang , Hui Zhai

Spread complexity uses the distribution of support of a time-evolving state in the Krylov basis to quantify dispersal across accessible dimensions of a Hilbert space. Here, we describe how variations in initial conditions, the Hamiltonian,…

High Energy Physics - Theory · Physics 2025-11-19 Vijay Balasubramanian , Pawel Caputa , Joan Simón

The spreading of quantum states in Krylov space under unitary dynamics provides a natural framework for characterizing quantum complexity. Quantifiers of this spreading, such as the spread complexity and the inverse participation ratio,…

Quantum Physics · Physics 2026-03-30 Swati Choudhary , Sukrut Mondkar , Ujjwal Sen

We consider the statistics of the results of a measurement of the spreading operator in the Krylov basis generated by the Hamiltonian of a quantum system starting from a specified initial pure state. We first obtain the probability…

Quantum Physics · Physics 2025-09-11 Yichao Fu , Keun-Young Kim , Kunal Pal , Kuntal Pal

Quantum complexity, suitably defined, has been suggested as an important probe of late-time dynamics of black holes, particularly in the context of AdS/CFT. A notion of quantum complexity can be effectively captured by quantifying the…

High Energy Physics - Theory · Physics 2022-04-20 E. Rabinovici , A. Sánchez-Garrido , R. Shir , J. Sonner

Krylov complexity has recently gained attention where the growth of operator complexity in time is measured in terms of the off-diagonal operator Lanczos coefficients. The operator Lanczos algorithm reduces the problem of complexity growth…

Quantum Physics · Physics 2024-09-23 Heiko Georg Menzler , Rishabh Jha

Recently, the concept of spread complexity, Krylov complexity for states, has been introduced as a measure of the complexity and chaoticity of quantum systems. In this paper, we study the spread complexity of the thermofield double state…

High Energy Physics - Theory · Physics 2024-05-27 Kyoung-Bum Huh , Hyun-Sik Jeong , Juan F. Pedraza

In this work, we investigate local quench dynamics in two-dimensional conformal field theories using Krylov space methods. We derive Lanczos coefficients, spread complexity, and Krylov entropies for local joining and splitting quenches in…

High Energy Physics - Theory · Physics 2025-10-21 Pawel Caputa , Giuseppe Di Giulio

We investigate phase transitions in a non-Hermitian Su-Schrieffer-Heeger (SSH) model with an imaginary chemical potential via Krylov spread complexity and Krylov fidelity. The spread witnesses the $\mathcal{PT}$-transition for the…

Strongly Correlated Electrons · Physics 2025-12-11 E. Medina-Guerra , I. V. Gornyi , Yuval Gefen

Krylov complexity (K-complexity) is a measure of quantum state complexity that minimizes wavefunction spreading across all the possible bases. It serves as a key indicator of operator growth and quantum chaos. In this work, K-complexity and…

Quantum Physics · Physics 2025-10-08 J. Bharathi Kannan , Sreeram PG , Sanku Paul , S. Harshini Tekur , M. S. Santhanam

In this paper, we investigate the dynamics of a non-Hermitian SSH model that arises out of the no-click limit of a monitored SSH model in the Krylov space. We find that the saturation timescale of the complexity associated with the spread…

Quantum Physics · Physics 2025-07-22 Nilachal Chakrabarti , Neha Nirbhan , Arpan Bhattacharyya

We investigate the anatomy and complexity of quantum states in Krylov space, in the ergodic and many-body localised (MBL) phases of a disordered, interacting spin chain. The Krylov basis generated by the Hamiltonian from an initial state…

Disordered Systems and Neural Networks · Physics 2026-03-27 Bikram Pain , David E. Logan , Sthitadhi Roy

We characterize the Many-Body Localization (MBL) phase transition using the dynamics of spread complexity and inverse participation ratio in the Krylov space starting from different initial states. Our analysis of the disordered Heisenberg…

Disordered Systems and Neural Networks · Physics 2024-09-05 Maitri Ganguli , Aneek Jana

We investigate the phase transitions from chaotic to nonchaotic dynamics in a quantum spin chain with a local non-Hermitian disorder, which can be realized with a Rydberg atom array setting. As the disorder strength increases, the emergence…

Quantum Physics · Physics 2025-10-03 Yijia Zhou , Wei Xia , Lin Li , Weibin Li

We study the behavior of spread complexity in the context of non-Hermitian many-body localization Transition (MBLT). Our analysis has shown that the singular value spread complexity is capable of distinguishing the ergodic and many-body…

Disordered Systems and Neural Networks · Physics 2024-11-19 Maitri Ganguli

We study how a machine based on deep learning algorithms learns Krylov spread complexity in quantum systems with N x N random Hamiltonians drawn from the Gaussian unitary ensemble. Using thermofield double states as initial conditions, we…

Quantum Physics · Physics 2025-11-19 Dongsu Bak , Su-Hyeong Kim , Sangnam Park , Jeong-Pil Song

The complexity of quantum states under dynamical evolution can be investigated by studying the spread with time of the state over a pre-defined basis. It is known that this complexity is minimised by choosing the Krylov basis, thus defining…

Quantum Physics · Physics 2024-09-04 Amin A. Nizami , Ankit W. Shrestha

Given the recent advances in quantum technology, the complexity of quantum states is an important notion. The idea of the Krylov spread complexity has come into focus recently with the goal of capturing this in a quantitative way. The…

Quantum Physics · Physics 2024-09-10 Bhilahari Jeevanesan

Commonly, the notion of "quantum chaos'' refers to the fast scrambling of information throughout complex quantum systems undergoing unitary evolution. Motivated by the Krylov complexity and the operator growth hypothesis, we demonstrate…

Quantum Physics · Physics 2024-09-19 Eoin Carolan , Anthony Kiely , Steve Campbell , Sebastian Deffner
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