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Swap Network Augmented Ansätze on Arbitrary Connectivity

Quantum Journal

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Researchers introduced an algorithm that optimizes qubit routing for arbitrary connectivity graphs, creating swap networks enabling direct interactions between any qubit pair on constrained quantum processors. The team embedded these swap networks into layered, connectivity-aware ansätze, co-designing circuit layers and routing to significantly improve trainability while reducing resource demands. Simulations of spin-glass and molecular electronic structure models demonstrated consistent performance gains, achieving lower energy errors with fewer entangling gates, shallower circuits, and reduced parameters. The approach outperformed standard hardware-efficient baselines and state-of-the-art routing methods, offering a practical solution for near-term quantum devices with limited qubit connectivity. Published in April 2026, this work provides a resource-efficient framework for capturing complex quantum correlations in hybrid algorithms on current noisy intermediate-scale quantum processors.

Swap Network Augmented Ansätze on Arbitrary Connectivity

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AbstractEfficient parametrizations of quantum states are essential for trainable hybrid classical-quantum algorithms. A key challenge in their design consists in adapting to the available qubit connectivity of the quantum processor, which limits the capacity to generate correlations between distant qubits in a resource-efficient and trainable manner. In this work we first introduce an algorithm that optimizes qubit routing for arbitrary connectivity graphs, resulting in a swap network that enables direct interactions between any pair of qubits. We then propose a co-design of circuit layers and qubit routing by embedding the derived swap networks within layered, connectivity-aware ansätze. This construction significantly improves the trainability of the ansatz, leading to enhanced performance with reduced resources. We showcase these improvements through ground-state simulations of strongly correlated systems, including spin-glass and molecular electronic structure models. Across exemplified connectivities, the swap-enhanced ansatz consistently achieves lower energy errors using fewer entangling gates, shallower circuits, and fewer parameters than standard layered-structured baselines. Our results indicate that swap network augmented ansätze provide enhanced trainability and resource-efficient design to capture complex correlations on devices with constrained qubit connectivity.Featured image: Optimized swap network on arbitrary connectivity.Popular summaryQuantum computers are limited by the fact that not all qubits can interact directly. This work shows that, instead of treating that as a problem to fix afterward, it can be built into the circuit design from the start. We develop optimized sequence of swaps, known as swap networks, that efficiently move quantum information across processors with arbitrary qubit connectivity, enabling quantum circuits to capture long-range correlations more effectively. In simulations of spin glasses and a challenging molecular system, the method achieves lower energy errors with shallower circuits, fewer entangling gates, and fewer parameters than standard hardware-efficient approaches or state-of-the art routing methods, pointing to a practical way to improve quantum simulations on today’s constrained devices.► BibTeX data@article{ParellaDilme2026swapnetwork, doi = {10.22331/q-2026-04-13-2062}, url = {https://doi.org/10.22331/q-2026-04-13-2062}, title = {Swap {N}etwork {A}ugmented {A}ns{\"{a}}tze on {A}rbitrary {C}onnectivity}, author = {Parella-Dilm{\'{e}}, Teodor and Kottmann, Jakob S. and Ac{\'{i}}n, Antonio}, journal = {{Quantum}}, issn = {2521-327X}, publisher = {{Verein zur F{\"{o}}rderung des Open Access Publizierens in den Quantenwissenschaften}}, volume = {10}, pages = {2062}, month = apr, year = {2026} }► References [1] M. Cerezo, Andrew Arrasmith, Ryan Babbush, Simon C. Benjamin, Suguru Endo, Keisuke Fujii, Jarrod R. McClean, Kosuke Mitarai, Xiao Yuan, Lukasz Cincio, and et al. ``Variational quantum algorithms''.

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Could not fetch ADS cited-by data during last attempt 2026-04-13 18:04:37: No response from ADS or unable to decode the received json data when getting the list of citing works.This Paper is published in Quantum under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. Copyright remains with the original copyright holders such as the authors or their institutions. AbstractEfficient parametrizations of quantum states are essential for trainable hybrid classical-quantum algorithms. A key challenge in their design consists in adapting to the available qubit connectivity of the quantum processor, which limits the capacity to generate correlations between distant qubits in a resource-efficient and trainable manner. In this work we first introduce an algorithm that optimizes qubit routing for arbitrary connectivity graphs, resulting in a swap network that enables direct interactions between any pair of qubits. We then propose a co-design of circuit layers and qubit routing by embedding the derived swap networks within layered, connectivity-aware ansätze. This construction significantly improves the trainability of the ansatz, leading to enhanced performance with reduced resources. We showcase these improvements through ground-state simulations of strongly correlated systems, including spin-glass and molecular electronic structure models. Across exemplified connectivities, the swap-enhanced ansatz consistently achieves lower energy errors using fewer entangling gates, shallower circuits, and fewer parameters than standard layered-structured baselines. Our results indicate that swap network augmented ansätze provide enhanced trainability and resource-efficient design to capture complex correlations on devices with constrained qubit connectivity.Featured image: Optimized swap network on arbitrary connectivity.Popular summaryQuantum computers are limited by the fact that not all qubits can interact directly. This work shows that, instead of treating that as a problem to fix afterward, it can be built into the circuit design from the start. We develop optimized sequence of swaps, known as swap networks, that efficiently move quantum information across processors with arbitrary qubit connectivity, enabling quantum circuits to capture long-range correlations more effectively. In simulations of spin glasses and a challenging molecular system, the method achieves lower energy errors with shallower circuits, fewer entangling gates, and fewer parameters than standard hardware-efficient approaches or state-of-the art routing methods, pointing to a practical way to improve quantum simulations on today’s constrained devices.► BibTeX data@article{ParellaDilme2026swapnetwork, doi = {10.22331/q-2026-04-13-2062}, url = {https://doi.org/10.22331/q-2026-04-13-2062}, title = {Swap {N}etwork {A}ugmented {A}ns{\"{a}}tze on {A}rbitrary {C}onnectivity}, author = {Parella-Dilm{\'{e}}, Teodor and Kottmann, Jakob S. and Ac{\'{i}}n, Antonio}, journal = {{Quantum}}, issn = {2521-327X}, publisher = {{Verein zur F{\"{o}}rderung des Open Access Publizierens in den Quantenwissenschaften}}, volume = {10}, pages = {2062}, month = apr, year = {2026} }► References [1] M. Cerezo, Andrew Arrasmith, Ryan Babbush, Simon C. Benjamin, Suguru Endo, Keisuke Fujii, Jarrod R. McClean, Kosuke Mitarai, Xiao Yuan, Lukasz Cincio, and et al. ``Variational quantum algorithms''.

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Swap Network Augmented Ansätze on Arbitrary Connectivity

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