NeQST — Publications

Publications: Qudit stabilizer codes for ZN lattice gauge theories with matter

Thu, 26 Feb 2026 00:00:00 +0000

Authors: Luca Spagnoli, Alessandro Roggero, and Nathan Wiebe

Journal reference: arXiv:2602.20661 [quant-ph] — Published February 26, 2026

In this work we extend the connection between Quantum Error Correction (QEC) and Lattice Gauge Theories (LGTs) by showing that a \(ZN\) gauge theory with prime dimension \(N\) coupled to dynamical matter can be expressed as a qudit stabilizer code. Using the stabilizer formalism we show how to formulate an exact mapping of the encoded \(ZN\) gauge theory onto two different bosonic models, uncovering a logical duality generated by error correction itself. From this perspective, quantum error correction provides a unifying language to expose dual descriptions of lattice gauge theories. In addition, we generalize earlier \(Z2\) constructions on qubits to \(ZN\) on \(N\)-level qudits and demonstrate how universal fault-tolerant gates can be implemented via state injection between compatible qudit codes.

Publications: Improving Quantum Multi-Objective Optimization with Archiving and Substitution

Wed, 11 Feb 2026 00:00:00 +0000

Authors: Linus Ekstrom, Takafumi Hosogi, Xavier Bonet-Monroig, Sebastian Schmitt, Hao Wang, and Thomas Bäck

Journal reference: Presented at The 11th International Conference on Machine Learning, Optimization, and Data Science (LOD) 2025 — Published February 11, 2026

Finding optimal solutions of conflicting objectives is a daily matter in many industrial applications, with multi-objective optimization trying to find the best solutions to them. The advent of quantum computing has led to researchers wondering if the promised exponential advantage can be obtained for these problems by variational quantum multi-objective optimization (QMOO) algorithm. Here, we improve it by introducing a Pareto Archive and dominated solutions substitution, clearly improving in hyper-volume convergence at additional quantum and classical cost. We propose the use of RMNK-landscapes as a unifying testbed for benchmarking QMOO, as it is common in classical multi-objective field. By devising a generic classical-to-quantum mapping of these landscapes, we perform a numerical hyperparameter tuning of QMOO, significantly enhancing its performance. Finally, we compare QMOO against well-known classical solvers for multi-objective tasks, NSGA-II/III, showing comparable results in small instances. Our results demonstrate that QMOO, when carefully tuned for the task at hand, might be advantageous on harder problems than its classical counterparts.

Publications: Fault-tolerant simulation of Lattice Gauge Theories with gauge covariant codes

Fri, 16 Jan 2026 00:00:00 +0000

Authors: Luca Spagnoli, Alessandro Roggero, and Nathan Wiebe

Journal reference: Quantum 10, 1968 — Published January 16, 2026

Preprint: arXiv:2405.19293 [quant-ph]

We show in this paper that a strong and easy connection exists between quantum error correction and Lattice Gauge Theories (LGT) by using the Gauge symmetry to construct an efficient error-correcting code for Abelian \(Z2\) LGTs. We identify the logical operations on this gauge covariant code and show that the corresponding Hamiltonian can be expressed in terms of these logical operations while preserving the locality of the interactions. Furthermore, we demonstrate that these substitutions actually give a new way of writing the LGT as an equivalent hardcore boson model. Finally we demonstrate a method to perform fault-tolerant time evolution of the Hamiltonian within the gauge covariant code using both product formulas and qubitization approaches. This opens up the possibility of inexpensive end to end dynamical simulations that save physical qubits by blurring the lines between simulation algorithms and quantum error correcting codes.