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  • Open Access

Splitting and Connecting Singlets in Atomic Quantum Circuits

Zijie Zhu, Yann Kiefer, Samuel Jele, Marius Gächter, Giacomo Bisson, Konrad Viebahn*, and Tilman Esslinger

  • Institute for Quantum Electronics and Quantum Center, ETH Zurich, 8093 Zurich, Switzerland

  • *Contact author: viebahnk@phys.ethz.ch
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Phys. Rev. X 15, 041032 – Published 18 November, 2025

DOI: https://doi.org/10.1103/xh3v-tky4

Abstract

Gate operations composed in quantum circuits form the basis for digital quantum simulation and quantum processing. While two-qubit gates generally operate on nearest neighbors, many circuits require nonlocal connectivity and necessitate some form of quantum information transport. Yet, connecting distant nodes of a quantum processor still remains challenging, particularly for neutral atoms in optical lattices. Here, we create singlet pairs of two magnetic states of fermionic potassium-40 atoms in an optical lattice and use a bidirectional topological Thouless pump to transport, coherently split, and separate the pairs, as well as to demonstrate interaction between them via tuneable (SWAP)α-gate operations. We achieve pumping with a single-shift fidelity of 99.78(3)% over 50 lattice sites and split the pairs within a decoherence-free subspace. Gates are implemented by superexchange interaction, allowing us to produce interwoven atomic singlets. For readout, we apply a magnetic field gradient, resulting in single- and multifrequency singlet-triplet oscillations. Our work shows avenues to create complex patterns of entanglement and new approaches to quantum processing, sensing, and atom interferometry.

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Popular Summary

Quantum information processing promises to solve problems far beyond the reach of classical computers, but doing so requires processors with very large numbers of qubits. Neutral atoms in optical lattices are a promising platform because they can be arranged at high density and with great uniformity. A key challenge, however, is connecting distant qubits in such crowded systems. In this study, we develop a way to build quantum circuits using a phenomenon called topological pumping, which acts like a microscopic Archimedes’ screw for atoms, moving them across the lattice with exceptional robustness.

The strength of this pump comes from its quantum nature. It allows atoms in a dense lattice to effectively “pass through” one another, with each atom moving in its own quantum lane. Using this property, we transport the two members of an entangled atom pair in opposite directions at the same time, stretching their entanglement across many lattice sites. When atoms from different entangled pairs are brought together again, we can make them interact to carry out programmable quantum gates.

This ability to reliably move, separate, and reconnect entangled atoms creates a toolbox for building complex quantum circuits. Our method demonstrates a scalable approach to linking qubits over long distances within compact systems, bringing neutral-atom quantum computers closer to practical reality.

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Phys. Rev. X 15, 041032– Published 18 November, 2025
  • Received 10 March 2025
  • Accepted 26 August 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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