Scalable modular architecture for universal quantum computation, by Fernando Gago-Encinas, Christiane P. Koch
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SciPost Physics Home Authoring Refereeing Submit a manuscript About Scalable modular architecture for universal quantum computation Fernando Gago-Encinas, Christiane P. Koch SciPost Phys. 20, 046 (2026) · published 17 February 2026 doi: 10.21468/SciPostPhys.20.2.046 pdf BiBTeX RIS Submissions/Reports Abstract Universal quantum computing requires the ability to perform every unitary operation, i.e., evolution operator controllability. In view of developing resource-efficient quantum processing units (QPUs), it is important to determine how many local controls and qubit-qubit couplings are required for controllability. Unfortunately, assessing the controllability of large qubit arrays is a difficult task, due to the exponential scaling of Hilbert space dimension. Here we show that it is sufficient to connect two qubit arrays that are evolution operator controllable by a single entangling two-qubit gate in order to obtain a composite qubit array that is evolution operator controllable. The proof provides a template to build up modular QPUs from smaller building blocks with reduced numbers of local controls and couplings. We illustrate the approach with two examples, consisting of 10, respectively 127 qubits, inspired by IBM quantum processors. × TY - JOURPB - SciPost FoundationDO - 10.21468/SciPostPhys.20.2.046TI - Scalable modular architecture for universal quantum computationPY - 2026/02/17UR - https://scipost.org/SciPostPhys.20.2.046JF - SciPost PhysicsJA - SciPost Phys.VL - 20IS - 2SP - 046A1 - Gago-Encinas, FernandoAU - Koch, Christiane P.AB - Universal quantum computing requires the ability to perform every unitary operation, i.e., evolution operator controllability. In view of developing resource-efficient quantum processing units (QPUs), it is important to determine how many local controls and qubit-qubit couplings are required for controllability. Unfortunately, assessing the controllability of large qubit arrays is a difficult task, due to the exponential scaling of Hilbert space dimension. Here we show that it is sufficient to connect two qubit arrays that are evolution operator controllable by a single entangling two-qubit gate in order to obtain a composite qubit array that is evolution operator controllable. The proof provides a template to build up modular QPUs from smaller building blocks with reduced numbers of local controls and couplings. We illustrate the approach with two examples, consisting of 10, respectively 127 qubits, inspired by IBM quantum processors.ER - × @Article{10.21468/SciPostPhys.20.2.046, title={{Scalable modular architecture for universal quantum computation}}, author={Fernando Gago-Encinas and Christiane P. Koch}, journal={SciPost Phys.}, volume={20}, pages={046}, year={2026}, publisher={SciPost}, doi={10.21468/SciPostPhys.20.2.046}, url={https://scipost.org/10.21468/SciPostPhys.20.2.046},} Ontology / Topics See full Ontology or Topics database. Quantum information Qubits Authors / Affiliations: mappings to Contributors and Organizations See all Organizations. 1 2 Fernando Gago-Encinas, 2 Christiane P. Koch 1 Deutsches Elektronen-Synchrotron / Deutsche Elektronen-Synchrotron DESY [DESY] 2 Freie Universität Berlin / Freie Universität Berlin [FU Berlin] Funders for the research work leading to this publication Brandenburger Staatsministerium für Wissenschaft, Forschung und Kultur Deutsche Forschungsgemeinschaft / German Research FoundationDeutsche Forschungsgemeinschaft [DFG]