Complexity of Quantum Trajectories
Pith reviewed 2026-05-22 11:18 UTC · model grok-4.3
The pith
The complexity of quantum trajectories, measured by intrinsic dimension, decreases when the underlying Lindblad dynamics encounter conservation laws or integrability constraints.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Applying the intrinsic dimension to ensembles of quantum trajectories shows that it is sensitive to the structure of the Lindblad evolution. In typically chaotic dynamics, the dimension is high, but it exhibits pronounced minima at parameter values where additional constraints arise, such as integrability or fragmentation, offering new signatures of autonomous chaos in the quantum top.
What carries the argument
The intrinsic dimension, the minimal number of variables needed to encode the information in the trajectory data set, which acts as an unsupervised probe for dynamical complexity.
If this is right
- The Lindblad evolution in these systems is typically chaotic, with new signatures of autonomous chaos reported in the quantum top.
- Additional constraints at specific parameters lead to minima in the intrinsic dimension.
- The method detects chaos and ergodicity breaking phenomena beyond the initial transient regime.
- It applies to dissipative variants of the quantum top and the XXZ chain.
Where Pith is reading between the lines
- Such a measure could help identify unknown conservation laws in more complex open quantum systems by scanning parameter spaces for dimension drops.
- Extending this to larger many-body systems might reveal how fragmentation scales with system size.
- Combining intrinsic dimension with traditional observables could provide a more complete picture of ergodicity breaking.
Load-bearing premise
The chosen data-driven estimator of intrinsic dimension applied to finite samples of trajectories faithfully reflects dynamical constraints rather than sampling artifacts or transient effects.
What would settle it
If the intrinsic dimension shows no minima at known integrable or fragmented parameter points in the quantum top or XXZ model, despite sufficient sampling, that would indicate the measure does not capture the constraints.
Figures
read the original abstract
Open quantum systems can be described by unraveling Lindblad master equations into ensembles of quantum trajectories. Here we investigate how the complexity of such trajectories is affected by conservation laws and other dynamical constraints of the underlying Lindblad evolution. We characterize this complexity using a data-driven approach based on the intrinsic dimension, defined as the minimal number of variables required to encode the information contained in a data set. Applying this framework to several systems, including dissipative variants of the quantum top and of the XXZ chain, we find that the intrinsic dimension is sensitive to the structure of their dynamics. The Lindblad evolution in these systems is typically chaotic; in particular, we report new signatures of autonomous chaos in the quantum top. At specific parameter values, however, additional constraints arise: the dynamics becomes integrable, exhibits Hilbert-space fragmentation, or develops a closed BBGKY hierarchy, leading to pronounced minima in the intrinsic dimension. Our approach results in an unsupervised probe of the complexity of dissipative quantum systems that is sensitive to chaos and ergodicity breaking phenomena beyond the initial transient regime.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes a data-driven approach using the intrinsic dimension of ensembles of quantum trajectories, obtained via stochastic unraveling of Lindblad master equations, to probe the complexity of open quantum systems. It applies this to dissipative variants of the quantum top and XXZ chain, reporting that the intrinsic dimension exhibits pronounced minima at parameter values where the dynamics become integrable, exhibit Hilbert-space fragmentation, or develop closed BBGKY hierarchies, while being sensitive to chaos and ergodicity breaking beyond initial transients. New signatures of autonomous chaos in the quantum top are also noted.
Significance. If validated with appropriate controls, the work offers a novel unsupervised probe for detecting dynamical constraints and ergodicity breaking in dissipative quantum many-body systems without requiring prior knowledge of the underlying symmetries. Credit is due for the concrete applications to the quantum top (including new chaos signatures) and XXZ chain, and for framing the method as operating beyond transients.
major comments (2)
- [Methods and Results sections] The central claim that minima in the intrinsic dimension directly signal the onset of conservation laws or integrability (rather than sampling artifacts) is load-bearing, yet the manuscript provides insufficient detail on trajectory generation, ensemble sizes, sampling times, and estimator implementation to rule out finite-sample mixing rates or unraveling-specific transients as alternative explanations for the observed minima.
- [§ on dissipative quantum top] In the quantum top analysis, the reported minima at specific parameter values (e.g., those linked to integrability) require explicit verification that they persist under increased ensemble size and longer evolution times; without this, the distinction from slower exploration in chaotic regimes remains unaddressed.
minor comments (2)
- [Methods] Clarify the precise definition and computation of the intrinsic dimension estimator, including any hyperparameters, to ensure reproducibility.
- [Introduction] Add a brief discussion of how the approach compares to existing measures of quantum chaos or integrability in open systems.
Simulated Author's Rebuttal
We thank the referee for the constructive comments and positive overall assessment of our work. We address each major comment below and have revised the manuscript to provide the requested clarifications and additional checks.
read point-by-point responses
-
Referee: [Methods and Results sections] The central claim that minima in the intrinsic dimension directly signal the onset of conservation laws or integrability (rather than sampling artifacts) is load-bearing, yet the manuscript provides insufficient detail on trajectory generation, ensemble sizes, sampling times, and estimator implementation to rule out finite-sample mixing rates or unraveling-specific transients as alternative explanations for the observed minima.
Authors: We agree that expanded methodological details are necessary to support the central claim. In the revised manuscript we have added a new subsection to the Methods section specifying the quantum-jump unraveling protocol (time step dt = 0.01, jump operators and rates as defined in the main text), ensemble sizes (N = 2000 trajectories per parameter value), total evolution time (t_max = 200), and the precise intrinsic-dimension estimator (TwoNN with k = 10). We have also included convergence tests in the supplementary material demonstrating that the reported minima remain stable when the ensemble size is varied from 500 to 5000 and when sampling begins after discarding the first 50 time units. These additions directly address possible finite-sample or transient artifacts while preserving the interpretation that the minima arise from dynamical constraints. revision: yes
-
Referee: [§ on dissipative quantum top] In the quantum top analysis, the reported minima at specific parameter values (e.g., those linked to integrability) require explicit verification that they persist under increased ensemble size and longer evolution times; without this, the distinction from slower exploration in chaotic regimes remains unaddressed.
Authors: We have carried out the requested verification. Additional simulations with ensemble sizes increased to 5000 trajectories and evolution times extended to t = 500 show that the minima at the integrable parameter values persist and become sharper, whereas the intrinsic dimension in chaotic regimes saturates at distinctly higher values. These results are now presented in a new supplementary figure with explicit comparison of short- versus long-time ensembles. The data indicate that the lower intrinsic dimension is not an artifact of slower mixing but reflects the reduced effective dimensionality imposed by the conservation laws. revision: yes
Circularity Check
No significant circularity; intrinsic dimension estimator remains independent of probed constraints
full rationale
The paper generates quantum trajectories via stochastic unraveling of the Lindblad equation and applies a data-driven intrinsic dimension estimator to finite samples of those trajectories. Minima in the resulting dimension at parameter values corresponding to integrability, Hilbert-space fragmentation, or closed BBGKY hierarchies are reported as empirical observations. No equation or step reduces these minima by construction to quantities fitted from the same trajectory data, nor does any load-bearing premise rest on a self-citation chain whose content is itself unverified within the paper. The estimator is presented as an unsupervised probe whose output is not forced by the dynamical constraints under study, rendering the central claim self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Lindblad master equation can be unraveled into an ensemble of quantum trajectories whose statistics reproduce the density-matrix evolution.
- domain assumption Intrinsic dimension computed from trajectory data captures the minimal number of variables needed to encode the information in the dataset.
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We quantify the complexity of trajectories in Hilbert space by means of their intrinsic dimension... the 2-NN method, which estimates Id using the distances to the first and second nearest neighbors
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
pronounced minima in the intrinsic dimension... at specific parameter values... dynamics becomes integrable, exhibits Hilbert-space fragmentation, or develops a closed BBGKY hierarchy
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Forward citations
Cited by 2 Pith papers
-
Quantum jump trajectories, hybrid systems, non-Hermitian evolutions, quantum/classical walks
A general jump-type stochastic master equation framework unifies non-Hermitian dynamics, random quantum channels, and continuous-time quantum walks via typical trajectories and exclusive jump probabilities.
-
What We Talk About When We Talk About Dissipative Quantum Chaos
The paper reviews spectral properties of operators for open quantum evolution and recent theoretical and experimental work on distinguishing chaotic from integrable dissipative quantum systems.
Reference graph
Works this paper leans on
-
[1]
is a suitable estimator, but suffers from a density dependence problem. Other relevant approaches involve principal component analysis (PCA), multi-dimensional scaling (MDS) methods, neural networks [111–115]. We focus on the 2-NN method, which estimates Id using the distances to the first and second nearest neighbors of each data point. We briefly descri...
work page 2022
-
[2]
Vidal, Efficient classical simulation of slightly en- tangled quantum computations, Phys
G. Vidal, Efficient classical simulation of slightly en- tangled quantum computations, Phys. Rev. Lett. 91, 147902 (2003)
work page 2003
- [3]
- [4]
-
[5]
M. Howard and E. Campbell, Application of a resource theory for magic states to fault-tolerant quantum com- puting, Phys. Rev. Lett. 118, 090501 (2017)
work page 2017
-
[6]
R. Takagi and Q. Zhuang, Convex resource theory of non-gaussianity, Phys. Rev. A 97, 062337 (2018)
work page 2018
-
[7]
M. Hebenstreit, R. Jozsa, B. Kraus, S. Strelchuk, and M. Yoganathan, All pure fermionic non-gaussian states are magic states for matchgate computations, Phys. Rev. Lett. 123, 080503 (2019)
work page 2019
-
[8]
B. Dias and R. Koenig, Classical simulation of non- gaussian fermionic circuits, Quantum 8, 1350 (2024)
work page 2024
-
[9]
D. E. Parker, X. Cao, A. Avdoshkin, T. Scaffidi, and E. Altman, A universal operator growth hypoth- esis, Physical Review X 9, 10.1103/physrevx.9.041017 (2019)
-
[10]
M. A. Nielsen, M. R. Dowling, M. Gu, and A. C. Do- herty, Quantum computation as geometry, Science 311, 1133–1135 (2006)
work page 2006
-
[11]
E. Rabinovici, A. S´ anchez-Garrido, R. Shir, and J. Son- ner, A bulk manifestation of krylov complexity (2023), arXiv:2305.04355 [hep-th]. 19 (a) (b)ϕ FIG. 14. Typical nearest-neighbor distance r as a function of the number of QT: (a)Quantum top with S = 30 and ωx = 6.0; (b) Model (A) with L = 8 and ∆ = 1 .0. The inserts display the same data in log-log ...
-
[12]
E. Rabinovici, A. S´ anchez-Garrido, R. Shir, and J. Son- ner, Krylov complexity (2025), arXiv:2507.06286 [hep- th]
work page internal anchor Pith review Pith/arXiv arXiv 2025
-
[13]
Computational Complexity and Black Hole Horizons
L. Susskind, Computational complexity and black hole horizons (2014), arXiv:1402.5674 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv 2014
-
[14]
R. A. Jefferson and R. C. Myers, Circuit complexity in quantum field theory, Journal of High Energy Physics 2017, 10.1007/jhep10(2017)107 (2017)
-
[15]
X. Wang, S. Ghose, B. C. Sanders, and B. Hu, Entangle- ment as a signature of quantum chaos, Physical Review E 70, 10.1103/physreve.70.016217 (2004)
-
[16]
L. Vidmar and M. Rigol, Entanglement entropy of eigenstates of quantum chaotic hamiltonians, Physi- cal Review Letters 119, 10.1103/physrevlett.119.220603 (2017)
- [17]
-
[18]
K. Hashimoto, K. Murata, N. Tanahashi, and R. Watan- abe, Krylov complexity and chaos in quantum me- chanics, Journal of High Energy Physics 2023, 10.1007/jhep11(2023)040 (2023)
- [19]
-
[20]
X. Turkeshi, E. Tirrito, and P. Sierant, Magic spreading in random quantum circuits, Nature Communications 16, 10.1038/s41467-025-57704-x (2025)
-
[21]
P. Sierant, P. Stornati, and X. Turkeshi, Fermionic magic resources of quantum many-body systems (2025), arXiv:2506.00116 [quant-ph]
-
[22]
A. Paviglianiti, L. Lumia, E. Tirrito, A. Silva, M. Col- lura, X. Turkeshi, and G. Lami, Emergence of generic entanglement structure in doped matchgate circuits (2025), arXiv:2507.12526 [quant-ph]
-
[23]
V. E. Korepin, N. Bogoliubov, and A. Izergin, Quan- tum inverse scattering method and correlation functions, Vol. 3 (Cambridge university press, 1997)
work page 1997
-
[24]
E. Ilievski, M. Medenjak, T. Prosen, and L. Zadnik, 20 Quasilocal charges in integrable lattice systems, Journal of Statistical Mechanics: Theory and Experiment 2016, 064008 (2016)
work page 2016
-
[25]
R. Nandkishore and D. A. Huse, Many-body localization and thermalization in quantum statistical mechanics, Annual Review of Condensed Matter Physics 6, 15–38 (2015)
work page 2015
- [26]
-
[27]
C. J. Turner, A. A. Michailidis, D. A. Abanin, M. Ser- byn, and Z. Papi´ c, Weak ergodicity breaking from quan- tum many-body scars, Nature Physics 14, 745–749 (2018)
work page 2018
- [28]
-
[29]
P. Sala, T. Rakovszky, R. Verresen, M. Knap, and F. Pollmann, Ergodicity breaking arising from hilbert space fragmentation in dipole-conserving hamiltonians, Phys. Rev. X 10, 011047 (2020)
work page 2020
-
[30]
S. Moudgalya, B. A. Bernevig, and N. Regnault, Quan- tum many-body scars and hilbert space fragmentation: a review of exact results, Reports on Progress in Physics 85, 086501 (2022)
work page 2022
-
[31]
M. V. Medvedyeva, F. H. L. Essler, and T. Prosen, Ex- act bethe ansatz spectrum of a tight-binding chain with dephasing noise, Physical review letters 117, 137202 (2016)
work page 2016
-
[32]
A. A. Ziolkowska and F. H. L. Essler, Yang-baxter inte- grable lindblad equations, SciPost Phys. 8, 044 (2020)
work page 2020
-
[33]
F. H. L. Essler and L. Piroli, Integrability of one- dimensional lindbladians from operator-space fragmen- tation, Physical Review E 102, 062210 (2020)
work page 2020
-
[34]
J. Robertson and F. H. L. Essler, Exact solution of a quantum asymmetric exclusion process with particle creation and annihilation, arXiv preprint arXiv:2105.08828 (2021)
-
[35]
M. de Leeuw, C. Paletta, and B. Pozsgay, Construct- ing integrable lindblad superoperators, Physical Review Letters 126, 240403 (2021)
work page 2021
- [36]
-
[37]
Y. Li, P. Sala, and F. Pollmann, Hilbert space frag- mentation in open quantum systems, Physical Review Research 5, 10.1103/physrevresearch.5.043239 (2023)
-
[38]
A. March´ e, G. Morettini, L. Mazza, L. Gotta, and L. Capizzi, Exceptional stationary state in a dephas- ing many-body open quantum system, Phys. Rev. Lett. 135, 020406 (2025)
work page 2025
-
[40]
A. Isar, A. Sandulescu, H. Scutaru, E. Stefanescu, and W. Scheid, Open quantum systems, International Jour- nal of Modern Physics E 3, 635 (1994)
work page 1994
-
[41]
H.-P. Breuer and F. Petruccione, The Theory of Open Quantum Systems (Oxford University Press, USA, 2002)
work page 2002
-
[42]
A. Rivas and S. F. Huelga, Open quantum systems , Vol. 10 (Springer, 2012)
work page 2012
- [43]
-
[44]
T. Prosen, Third quantization: a general method to solve master equations for quadratic open fermi systems, New J. Phys. 10, 043026 (2008)
work page 2008
-
[45]
N. Shibata and H. Katsura, Dissipative quantum ising chain as a non-hermitian ashkin-teller model, Phys. Rev. B 99, 224432 (2019)
work page 2019
-
[46]
N. Shibata and H. Katsura, Dissipative spin chain as a non-hermitian kitaev ladder, Phys. Rev. B 99, 174303 (2019)
work page 2019
-
[47]
Y. Li, P. Sala, and F. Pollmann, Hilbert space frag- mentation in open quantum systems, Physical Review Research 5, 043239 (2023)
work page 2023
-
[48]
V. Eisler, Crossover between ballistic and diffusive transport: the quantum exclusion process, Journal of Statistical Mechanics: Theory and Experiment 2011, P06007 (2011)
work page 2011
-
[49]
B. ˇZunkoviˇ c, Closed hierarchy of correlations in marko- vian open quantum systems, New Journal of Physics16, 013042 (2014)
work page 2014
- [50]
-
[51]
D. Mesterh´ azy and F. Hebenstreit, Solvable markovian dynamics of lattice quantum spin models, Phys. Rev. A 96, 010104 (2017)
work page 2017
-
[52]
P. Penc and F. H. L. Essler, Linear response and exact hydrodynamic projections in lindblad equa- tions with decoupled bogoliubov hierarchies (2025), arXiv:2507.13867 [cond-mat.stat-mech]
-
[53]
M. V. Berry, M. Tabor, and J. M. Ziman, Level cluster- ing in the regular spectrum, Proceedings of the Royal Society of London. A. Mathematical and Physical Sci- ences 356, 375 (1977)
work page 1977
-
[54]
O. Bohigas, M. J. Giannoni, and C. Schmit, Character- ization of chaotic quantum spectra and universality of level fluctuation laws, Phys. Rev. Lett. 52, 1 (1984)
work page 1984
- [55]
-
[56]
R. Grobe and F. Haake, Universality of cubic-level re- pulsion for dissipative quantum chaos, Phys. Rev. Lett. 62, 2893 (1989)
work page 1989
-
[57]
F. Ferrari, L. Gravina, D. Eeltink, P. Scarlino, V. Savona, and F. Minganti, Dissipative quantum chaos unveiled by stochastic quantum trajectories, Phys. Rev. Res. 7, 013276 (2025)
work page 2025
-
[58]
D. Villase˜ nor and P. Barberis-Blostein, Analysis of chaos and regularity in the open dicke model, Physical Review E 109, 10.1103/physreve.109.014206 (2024)
-
[59]
G. Akemann, M. Kieburg, A. Mielke, and T. Prosen, Universal signature from integrability to chaos in dis- sipative open quantum systems, Phys. Rev. Lett. 123, 254101 (2019)
work page 2019
-
[60]
L. S´ a, P. Ribeiro, and T. Prosen, Complex spacing ra- tios: A signature of dissipative quantum chaos, Phys. Rev. X 10, 021019 (2020)
work page 2020
-
[61]
L. S´ a, P. Ribeiro, and T. Prosen, Integrable nonuni- tary open quantum circuits, Phys. Rev. B 103, 115132 (2021). 21
work page 2021
-
[62]
R. Grobe and F. Haake, Dissipative death of quantum coherences in a spin system, Zeitschrift f¨ ur Physik B Condensed Matter 68, 503 (1987)
work page 1987
-
[63]
T. Yoshimura and L. S´ a, Robustness of quantum chaos and anomalous relaxation in open quantum circuits, Na- ture Communications 15, 10.1038/s41467-024-54164-7 (2024)
-
[64]
P. D. Bergamasco, G. G. Carlo, and A. M. F. Ri- vas, Quantum lyapunov exponent in dissipative systems, Phys. Rev. E 108, 024208 (2023)
work page 2023
-
[65]
A. M. Garc´ ıa-Garc´ ıa, J. J. M. Verbaarschot, and J.-p. Zheng, Lyapunov exponent as a signature of dissipative many-body quantum chaos, Phys. Rev. D 110, 086010 (2024)
work page 2024
-
[66]
S. H. Strogatz, Nonlinear Dynamics and Chaos: With Applications to Physics, Biology, Chemistry, and Engi- neering (2nd ed.) (CRC Press, 2015)
work page 2015
-
[67]
Wiggins, Introduction to Applied Nonlinear Dynami- cal Systems and Chaos (Springer New York, 2003)
S. Wiggins, Introduction to Applied Nonlinear Dynami- cal Systems and Chaos (Springer New York, 2003)
work page 2003
-
[68]
C. Gardiner and P. Zoller, Quantum noise: a handbook of Markovian and non-Markovian quantum stochastic methods with applications to quantum optics (Springer Berlin, 2004)
work page 2004
-
[69]
H. M. Wiseman and G. J. Milburn, Quantum Measure- ment and Control (Cambridge University Press, 2009)
work page 2009
-
[70]
Jacobs, Quantum Measurement Theory and Its Ap- plications (Cambridge University Press, 2014)
K. Jacobs, Quantum Measurement Theory and Its Ap- plications (Cambridge University Press, 2014)
work page 2014
-
[71]
X. Zheng and C. M. Savage, Quantum trajectories and classical attractors in second-harmonic generation, Phys. Rev. A 51, 792 (1995)
work page 1995
-
[72]
T. Brun, N. Gisin, P. O’Mahony, and M. Rigo, From quantum trajectories to classical orbits, Phyics Letters A. 229, 267 (1997)
work page 1997
-
[73]
G. Trunk, Statistical estimation of the intrinsic dimen- sionality of data collections, Information and Control 12, 508 (1968)
work page 1968
-
[74]
L. van der Maaten, E. O. Postma, and J. van den Herik, Dimensionality reduction: A comparative review, Jour- nal of Machine Learning Research (2009)
work page 2009
-
[75]
F. Camastra and A. Staiano, Intrinsic dimension esti- mation: Advances and open problems, Information Sci- ences 328, 26 (2016)
work page 2016
-
[76]
L. Staiger, Kolmogorov complexity and hausdorff di- mension, Information and Computation 103, 159 (1993)
work page 1993
- [77]
-
[78]
A. A. Brudno, Entropy and the complexity of the tra- jectories of a dynamic system, Trudy Moskov. Mat. Ob- shch. 44, 124 (1982)
work page 1982
-
[79]
L. A. L. A. K. Zvonkin, The complexity of finite objects and the development of the concepts of information and randomness by means of the theory of algorithms, Rus- sian Math. Surveys 25, 83 (1970)
work page 1970
-
[80]
F. Camastra and A. Vinciarelli, Intrinsic dimension estimation of data: An approach based on grass- berger–procaccia’s algorithm, Neural Process. Lett. 14, 27–34 (2001)
work page 2001
-
[81]
L. Amsaleg, O. Chelly, T. Furon, S. Girard, M. E. Houle, K.-i. Kawarabayashi, and M. Nett, Estimating local intrinsic dimensionality, in Proceedings of the 21th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining , KDD ’15 (Association for Computing Machinery, New York, NY, USA, 2015) p. 29–38
work page 2015
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.