Combining non-parametric quantum states and MERA tensor networks for ground-state optimization
Pith reviewed 2026-05-21 04:13 UTC · model grok-4.3
The pith
Hybrid setup fixes quantum-annealed states as boundaries in classical MERA to raise ground-state accuracy at fixed circuit depth.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Treating a quantum state prepared by annealing as a non-variational fixed boundary tensor via classical shadows, then variationally optimizing an isometric MERA tensor network around it, produces higher-accuracy ground-state approximations for the transverse-field Ising model than the original quantum state alone, while quantum circuit depth stays the same and the optimization tolerates noise.
What carries the argument
Fixed boundary tensor obtained from classical shadows of the non-parametric quantum-annealed state, used as a static resource during classical variational optimization of the isometric MERA network.
If this is right
- The hybrid approach delivers better ground-state approximations for spin chains without any increase in quantum circuit resources.
- Noise robustness indicates the method can run on current quantum hardware with classical post-processing.
- Classical variational optimization of the tensor network compensates for imperfections in the quantum-prepared state.
- The setup keeps quantum depth constant while scaling the classical tensor network size.
Where Pith is reading between the lines
- The fixed-boundary idea could transfer to other tensor networks such as MPS or tree tensor networks for similar hybrid gains.
- Off-loading part of the state to a fixed classical resource may ease barren-plateau issues in variational quantum eigensolvers.
- Testing the same construction on two-dimensional lattices or molecular Hamiltonians would test generality.
- Pairing the method with error mitigation on the quantum side could compound accuracy improvements.
Load-bearing premise
The quantum state from annealing can be faithfully represented by classical shadows so that it functions as a useful fixed boundary tensor improving the MERA optimization beyond what the quantum state achieves by itself.
What would settle it
Compare ground-state energy error or fidelity obtained from the hybrid MERA-plus-fixed-boundary method against the pure quantum simulation on the transverse-field Ising model at identical circuit depth, both with and without added statistical or hardware noise.
Figures
read the original abstract
Hybrid tensor networks offer a promising route to enhance the expressivity of classical tensor network methods by incorporating quantum states prepared on a quantum computer. Existing approaches are limited by the variational optimization of the quantum component of the tensor network. In this work, we introduce an alternative strategy that combines a non-parametric quantum state prepared through quantum annealing and a classical isometric tensor network. The latter is variationally optimized while the former is used as a fixed, boundary tensor resource in the form of classical shadows. We demonstrate the feasibility of this approach through extensive numerical simulations on the transverse-field Ising model, showing that the optimization procedure remains robust under statistical and hardware noise. Moreover, our results indicate that our newly proposed setup improves the accuracy of the obtained ground state approximation compared to the original quantum simulation, without increasing the depth of the applied quantum circuits. Therefore, this setup offers a practical route to scale variational quantum algorithms towards the quantum utility scale.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes a hybrid approach to ground-state optimization that combines a non-parametric quantum state prepared via quantum annealing (represented as a fixed boundary tensor using classical shadows) with a variationally optimized classical isometric MERA tensor network. Numerical simulations on the transverse-field Ising model are used to demonstrate robustness under statistical and hardware noise, with the hybrid setup claimed to yield higher accuracy than the pure quantum simulation baseline without requiring deeper quantum circuits.
Significance. If the central claim holds, the work provides a concrete route to incorporate quantum resources into classical tensor networks as fixed, non-variational elements, potentially improving expressivity and accuracy in variational quantum algorithms while keeping circuit depth fixed. The TFIM numerics supply a reproducible test case, though no machine-checked proofs or parameter-free derivations are reported.
major comments (1)
- The accuracy improvement over the pure quantum baseline is load-bearing for the central claim, yet the manuscript provides no explicit quantification of how finite-shot statistical errors or truncation in the classical-shadow boundary tensor propagate through the isometric MERA layers (see the section describing the boundary-tensor construction and the numerical-results section). A direct comparison of MERA optimization with the exact quantum boundary versus its classical-shadow approximation is needed to rule out the possibility that observed gains arise from classical optimization alone rather than the hybrid quantum resource.
minor comments (2)
- Notation for the isometric MERA tensors and the classical-shadow boundary could be unified across text and figures to avoid ambiguity in how the fixed quantum state enters the network.
- The abstract mentions 'extensive numerical simulations' but does not specify system sizes, number of shots, or noise models; adding these details would improve reproducibility.
Simulated Author's Rebuttal
We thank the referee for their careful reading of the manuscript and for the constructive major comment. We address the point in detail below and have revised the manuscript to incorporate additional comparisons and analysis as suggested.
read point-by-point responses
-
Referee: The accuracy improvement over the pure quantum baseline is load-bearing for the central claim, yet the manuscript provides no explicit quantification of how finite-shot statistical errors or truncation in the classical-shadow boundary tensor propagate through the isometric MERA layers (see the section describing the boundary-tensor construction and the numerical-results section). A direct comparison of MERA optimization with the exact quantum boundary versus its classical-shadow approximation is needed to rule out the possibility that observed gains arise from classical optimization alone rather than the hybrid quantum resource.
Authors: We agree that explicitly ruling out purely classical contributions strengthens the central claim. In the revised manuscript we have added a new figure and accompanying text in the numerical-results section that directly compares three cases on small system sizes (where exact simulation of the boundary tensor remains feasible): (i) the hybrid MERA with the exact quantum boundary tensor, (ii) the hybrid MERA with the classical-shadow approximation of the same boundary, and (iii) a purely classical isometric MERA using a standard product-state boundary. The results show that the accuracy gain persists when the exact quantum boundary is used and that the classical-shadow version retains most of this gain, with the difference attributable to finite-shot noise rather than to the classical optimization procedure itself. We have also added a brief propagation analysis: we vary the number of shots used to construct the classical-shadow boundary tensor and track the resulting change in the final variational energy after MERA optimization; the energy remains stable within the reported error bars for the shot counts employed in the original experiments. These additions are now included in the revised version of the paper. revision: yes
Circularity Check
No significant circularity; hybrid method validated by external numerical simulations
full rationale
The paper proposes a hybrid setup using a fixed non-parametric quantum state (from annealing) as a classical-shadow boundary tensor in an isometric MERA network, with the MERA tensors variationally optimized. The claimed accuracy improvement over pure quantum simulation is demonstrated through numerical experiments on the transverse-field Ising model under statistical and hardware noise. This rests on empirical results rather than any derivation that reduces by construction to the inputs. No self-definitional steps, fitted parameters renamed as predictions, or load-bearing self-citations appear in the presented chain. The approach is self-contained against the reported benchmarks.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Quantum annealing produces usable non-parametric states that can be represented via classical shadows without significant loss for tensor-network boundary conditions.
- domain assumption MERA tensor networks can be variationally optimized when supplied with an external boundary tensor derived from quantum measurements.
Reference graph
Works this paper leans on
-
[1]
Riemannian optimization of isometric tensor networks All the tensors entering the MERA layers are either isometries or unitaries. Therefore, they can be opti- mized with a global, gradient-based Riemannian opti- mization constrained on the manifold of isometric ma- tricesM[54–56]. Together with the calculation of gradi- ents via automatic differentiation ...
-
[2]
S. R. White, Density matrix formulation for quantum renormalization groups, Phys. Rev. Lett.69, 2863 (1992)
work page 1992
- [3]
-
[4]
S. ¨Ostlund and S. Rommer, Thermodynamic limit of den- sity matrix renormalization, Phys. Rev. Lett.75, 3537 (1995)
work page 1995
-
[5]
Renormalization algorithms for Quantum-Many Body Systems in two and higher dimensions
F. Verstraete and J. I. Cirac, Renormalization algorithms for quantum-many body systems in two and higher di- mensions, arXiv preprint cond-mat/0407066 (2004)
work page internal anchor Pith review Pith/arXiv arXiv 2004
- [6]
-
[7]
Vidal, Class of quantum many-body states that can be efficiently simulated, Phys
G. Vidal, Class of quantum many-body states that can be efficiently simulated, Phys. Rev. Lett.101, 110501 (2008)
work page 2008
-
[8]
G. Evenbly and G. Vidal, Class of highly entangled many- body states that can be efficiently simulated, Phys. Rev. Lett.112, 240502 (2014). 12 (a) 0 10 20 30 40 50 Iteration −30.45 −30.40 −30.35 −30.30 −30.25 −30.20 −30.15 −30.10 Energy Initial Energy Exact Energy Exact evaluation Training POVMs ( S = 10 6) Validation POVMs ( S = 10 6) (b) 0 10 20 30 40 5...
work page 2014
-
[9]
Vidal, Efficient simulation of one-dimensional quan- tum many-body systems, Phys
G. Vidal, Efficient simulation of one-dimensional quan- tum many-body systems, Phys. Rev. Lett.93, 040502 (2004)
work page 2004
-
[10]
Schollw¨ ock, The density-matrix renormalization group in the age of matrix product states, Ann
U. Schollw¨ ock, The density-matrix renormalization group in the age of matrix product states, Ann. Phys.326, 96 (2011)
work page 2011
-
[11]
R. Or´ us, A practical introduction to tensor networks: Matrix product states and projected entangled pair states, Ann. Phys.349, 117 (2014)
work page 2014
-
[12]
Or´ us, Tensor networks for complex quantum systems, Nat
R. Or´ us, Tensor networks for complex quantum systems, Nat. Rev. Phys.1, 538 (2019)
work page 2019
-
[13]
J. I. Cirac, D. Perez-Garcia, N. Schuch, and F. Ver- straete, Matrix product states and projected entangled pair states: Concepts, symmetries, theorems, Rev. Mod. Phys.93, 045003 (2021)
work page 2021
-
[14]
G. Evenbly and G. Vidal, Tensor network states and ge- ometry, J. Stat. Phys.145, 891 (2011)
work page 2011
- [15]
-
[16]
F. Verstraete and J. I. Cirac, Matrix product states rep- resent ground states faithfully, Phys. Rev. B73, 094423 (2006)
work page 2006
-
[17]
M. B. Hastings, An area law for one-dimensional quan- tum systems, J. Stat. Mech.: Theory Exp.2007(08), P08024
work page 2007
- [18]
-
[19]
J. Haferkamp, D. Hangleiter, J. Eisert, and M. Gluza, Contracting projected entangled pair states is average- case hard, Phys. Rev. Res.2, 013010 (2020)
work page 2020
-
[20]
X. Yuan, J. Sun, J. Liu, Q. Zhao, and Y. Zhou, Quantum simulation with hybrid tensor networks, Phys. Rev. Lett. 127, 040501 (2021)
work page 2021
-
[21]
J. Schuhmacher, M. Ballarin, A. Baiardi, G. Magnifico, F. Tacchino, S. Montangero, and I. Tavernelli, Hybrid tree tensor networks for quantum simulation, PRX Quan- tum6, 010320 (2025)
work page 2025
-
[22]
J. R. McClean, S. Boixo, V. N. Smelyanskiy, R. Babbush, and H. Neven, Barren plateaus in quantum neural net- work training landscapes, Nat. Commun.9, 4812 (2018)
work page 2018
-
[23]
S. Wang, E. Fontana, M. Cerezo, K. Sharma, A. Sone, L. Cincio, and P. J. Coles, Noise-induced barren plateaus in variational quantum algorithms, Nat. Commun.12, 6961 (2021)
work page 2021
-
[24]
S. Thanasilp, S. Wang, N. A. Nghiem, P. Coles, and M. Cerezo, Subtleties in the trainability of quantum machine learning models, Quantum Mach. Intell.5, 21 (2023)
work page 2023
-
[25]
A. B. Finnila, M. A. Gomez, C. Sebenik, C. Stenson, and J. D. Doll, Quantum annealing: A new method for min- imizing multidimensional functions, Chem. Phys. Lett. 219, 343 (1994). 13
work page 1994
-
[26]
T. Kadowaki and H. Nishimori, Quantum annealing in the transverse ising model, Phys. Rev. E58, 5355 (1998)
work page 1998
- [27]
-
[28]
T. Albash and D. A. Lidar, Adiabatic quantum compu- tation, Rev. Mod. Phys.90, 015002 (2018)
work page 2018
-
[29]
G. Gentinetta, F. Metz, and G. Carleo, Correcting and extending trotterized quantum many-body dynamics, PRX Quantum6, 030361 (2025)
work page 2025
-
[30]
Y. Kim, A. Eddins, S. Anand, K. X. Wei, E. Van Den Berg, S. Rosenblatt, H. Nayfeh, Y. Wu, M. Zale- tel, K. Temme,et al., Evidence for the utility of quan- tum computing before fault tolerance, Nature618, 500 (2023)
work page 2023
-
[31]
H. Yu, Y. Zhao, and T.-C. Wei, Simulating large-size quantum spin chains on cloud-based superconducting quantum computers, Phys. Rev. Res.5, 013183 (2023)
work page 2023
-
[32]
R. C. Farrell, M. Illa, A. N. Ciavarella, and M. J. Sav- age, Quantum simulations of hadron dynamics in the schwinger model using 112 qubits, Phys. Rev. D109, 114510 (2024)
work page 2024
-
[33]
A. Miessen, D. J. Egger, I. Tavernelli, and G. Mazzola, Benchmarking digital quantum simulations above hun- dreds of qubits using quantum critical dynamics, PRX Quantum5, 040320 (2024)
work page 2024
-
[34]
T. A. Chowdhury, K. Yu, M. A. Shamim, M. Kabir, and R. S. Sufian, Enhancing quantum utility: simulat- ing large-scale quantum spin chains on superconducting quantum computers, Phys. Rev. Res.6, 033107 (2024)
work page 2024
-
[35]
T. A. Cochran, B. Jobst, E. Rosenberg, Y. D. Lensky, G. Gyawali, N. Eassa, M. Will, A. Szasz, D. Abanin, R. Acharya,et al., Visualizing dynamics of charges and strings in (2+1) d lattice gauge theories, Nature , 1 (2025)
work page 2025
-
[36]
Digital quantum magnetism on a trapped-ion quantum computer
R. Haghshenas, E. Chertkov, M. Mills, W. Kadow, S.- H. Lin, Y.-H. Chen, C. Cade, I. Niesen, T. Beguˇ si´ c, M. S. Rudolph,et al., Digital quantum magnetism at the frontier of classical simulations, arXiv preprint arXiv:2503.20870 (2025)
work page internal anchor Pith review Pith/arXiv arXiv 2025
- [37]
-
[38]
N. A. Zemlevskiy, Scalable quantum simulations of scat- tering in scalar field theory on 120 qubits, Phys. Rev. D 112, 034502 (2025)
work page 2025
-
[39]
J. Schuhmacher, G.-X. Su, J. J. Osborne, A. Gandon, J. C. Halimeh, and I. Tavernelli, Observation of hadron scattering in a lattice gauge theory on a quantum com- puter, arXiv preprint arXiv:2505.20387 (2025)
- [40]
-
[41]
G. Evenbly and G. Vidal, Algorithms for entanglement renormalization, Phys. Rev. B79, 144108 (2009)
work page 2009
- [42]
-
[43]
A. Acharya, S. Saha, and A. M. Sengupta, Shadow to- mography based on informationally complete positive operator-valued measure, Phys. Rev. A104, 052418 (2021)
work page 2021
- [44]
-
[45]
B. Vermersch, M. Ljubotina, J. I. Cirac, P. Zoller, M. Ser- byn, and L. Piroli, Many-body entropies and entangle- ment from polynomially many local measurements, Phys. Rev. X14, 031035 (2024)
work page 2024
- [46]
-
[47]
G. Garc´ ıa-P´ erez, E.-M. Borrelli, M. Leahy, J. Malmi, S. Maniscalco, M. A. C. Rossi, B. Sokolov, and D. Caval- canti, Virtual linear map algorithm for classical boost in near-term quantum computing (2022), arXiv:2207.01360 [quant-ph]
-
[48]
S. Filippov, B. Sokolov, M. A. Rossi, J. Malmi, E.-M. Borrelli, D. Cavalcanti, S. Maniscalco, and G. Garc´ ıa- P´ erez, Matrix product channel: Variationally optimized quantum tensor network to mitigate noise and reduce errors for the variational quantum eigensolver, arXiv preprint arXiv:2212.10225 (2022)
-
[49]
A. A. Akhtar, H.-Y. Hu, and Y.-Z. You, Scalable and Flexible Classical Shadow Tomography with Tensor Net- works, Quantum7, 1026 (2023)
work page 2023
-
[50]
S. Filippov, M. Leahy, M. A. Rossi, and G. Garc´ ıa-P´ erez, Scalable tensor-network error mitigation for near-term quantum computing, arXiv preprint arXiv:2307.11740 (2023)
-
[51]
S. Mangini and D. Cavalcanti, Low variance estima- tions of many observables with tensor networks and informationally-complete measurements, Quantum9, 1812 (2025)
work page 2025
- [52]
-
[53]
M. Larocca, S. Thanasilp, S. Wang, K. Sharma, J. Bia- monte, P. J. Coles, L. Cincio, J. R. McClean, Z. Holmes, and M. Cerezo, Barren plateaus in variational quantum computing, Nat. Rev. Phys.7, 174 (2025)
work page 2025
-
[54]
A. Miessen, P. J. Ollitrault, F. Tacchino, and I. Taver- nelli, Quantum algorithms for quantum dynamics, Nat. Comput. Sci.3, 25 (2023)
work page 2023
- [55]
-
[56]
I. A. Luchnikov, M. E. Krechetov, and S. N. Filippov, Riemannian geometry and automatic differentiation for optimization problems of quantum physics and quantum technologies, New J. Phys.23, 073006 (2021)
work page 2021
- [57]
-
[58]
A. G. Baydin, B. A. Pearlmutter, A. A. Radul, and J. M. Siskind, Automatic differentiation in machine learning: a survey, J. Mach. Learn. Res.18, 1 (2018)
work page 2018
-
[59]
D. P. Kingma, Adam: A method for stochastic optimiza- tion, arXiv preprint arXiv:1412.6980 (2014)
work page internal anchor Pith review Pith/arXiv arXiv 2014
- [60]
- [61]
- [62]
- [63]
-
[64]
G. Garc´ ıa-P´ erez, M. A. Rossi, B. Sokolov, F. Tacchino, P. K. Barkoutsos, G. Mazzola, I. Tavernelli, and S. Man- iscalco, Learning to measure: Adaptive informationally complete generalized measurements for quantum algo- rithms, Prx quantum2, 040342 (2021)
work page 2021
-
[65]
L. E. Fischer, T. Dao, I. Tavernelli, and F. Tacchino, Dual-frame optimization for informationally complete quantum measurements, Phys. Rev. A109, 062415 (2024)
work page 2024
-
[66]
A. Caprotti, J. Morris, and B. Daki´ c, Optimizing quan- tum tomography via shadow inversion, Phys. Rev. Res. 6, 033301 (2024)
work page 2024
-
[67]
K. Korhonen, S. Mangini, J. Malmi, H. Vappula, and D. Cavalcanti, Improving shadow estimation with locally- optimal dual frames, arXiv preprint arXiv:2511.02555 (2025)
-
[68]
N. Hatano and M. Suzuki, Finding exponential prod- uct formulas of higher orders, inQuantum annealing and other optimization methods(Springer, 2005) pp. 37–68
work page 2005
-
[69]
How to Build a Quantum Supercomputer: Scaling from Hundreds to Millions of Qubits
M. Mohseni, A. Scherer, K. G. Johnson, O. Wertheim, M. Otten, N. A. Aadit, Y. Alexeev, K. M. Bresniker, K. Y. Camsari, B. Chapman,et al., How to build a quan- tum supercomputer: Scaling from hundreds to millions of qubits, arXiv preprint arXiv:2411.10406 (2024)
work page internal anchor Pith review Pith/arXiv arXiv 2024
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.