Quantum computing represents a central challenge in modern science. Neutral atoms in optical lattices have emerged as a leading computing platform, with collisional gates offering a stable mechanism for quantum logic1–10.
Quantum computing represents a central challenge in modern science. Neutral atoms in optical lattices have emerged as a leading computing platform, with collisional gates offering a stable mechanism for quantum logic, which obscures the underlying quantum geometry and quantum statistics crucial for realizing intrinsically robust operations.
Here we propose and experimentally demonstrate a purely geometric two-qubit SWAP gate by transiently populating qubit doublon states of fermionic atoms in a dynamical optical lattice. The presence of these doublon states, together with fermionic exchange anti-symmetry, enables a two-particle quantum holonomy—a geometric evolution in which dynamical phases are absent. This yields a gate mechanism that is intrinsically protected against fluctuations and inhomogeneities of the confining potentials. The resilience of the gate is further reinforced by time-reversal and chiral symmetries of the Hamiltonian. We experimentally validate this exceptional protection, achieving a loss-corrected amplitude fidelity of 99.91% measured across the entire system consisting of more than 17,000 atom pairs. When combined with recently developed topological pumping methods for atom transport, our results pave the way for large-scale, highly connected quantum processors. This work introduces a new model for quantum logic that transforms fundamental symmetries, including quantum statistics, into a powerful resource for fault-tolerant computation.Fig. 1: Two-qubit gates realized by populating qubit doublon states.Fig. 3: Fidelity and robustness of the geometric SWAP gate.Jaksch, D., Briegel, H.-J., Cirac, J. I., Gardiner, C. W. & Zoller, P. Entanglement of atoms via cold controlled collisions.Google ScholarSingh, J., Reuter, J. A.P., Calarco, T., Motzoi, F. & Zeier, R. Optimizing two-qubit gates for ultracold atoms using Fermi-Hubbard models.Trotzky, S., Chen, Y.-A., Schnorrberger, U., Cheinet, P. & Bloch, I. Controlling and detecting spin correlations of ultracold atoms in optical lattices.Google ScholarVitanov, N. V., Rangelov, A. A., Shore, B. W. & Bergmann, K. Stimulated Raman adiabatic passage in physics, chemistry, and beyond.Greif, D., Uehlinger, T., Jotzu, G., Tarruell, L. & Esslinger, T. Short-range quantum magnetism of ultracold fermions in an optical lattice.Tan, B. & Cong, J. Optimal layout synthesis for quantum computing. InRines, R. et al. Demonstration of a logical architecture uniting motion and in-place entanglement: Shor’s algorithm, constant-depth CNOT ladder, and many-hypercube code. Preprint atZhu, C. et al. Quantum compiler design for qubit mapping and routing: a cross-architectural survey of superconducting, trapped-ion, and neutral atom systems. Preprint atWe thank A. Frank for assistance with electronics equipment. We acknowledge funding by the Swiss National Science Foundation . Y.K. acknowledges funding from the ETH Postdoctoral Fellowship 24-2 FEL-035.Institute for Quantum Electronics and Quantum Center, ETH Zurich, Zurich, Switzerland Y.K., Z.Z. and L.F. measured and analysed the data. K.V. and T.E. supervised the work. Y.K., Z.Z., L.F., S.J., M.G., G.B., K.V. and T.E. contributed to planning the experiment, discussions and preparation of the manuscript. Extended Data Fig. 1 Singlet-triplet-oscillation measurement protocol and two-particle Bloch sphere.. The energy offset dynamically couples the singlet and triplet states visualised as a rotation on the two-particle Bloch sphere around the-axis. The time trace of the singlet fraction with an applied magnetic field gradient. The amplitude of the STO signal determines the returning fidelity afterstate. The decay of the oscillation offset is a result of the dissipative loss of atoms in the lattice. A phase shift is induced by a light shift in the optical lattice, which can be corrected for using standard dynamical decoupling protocols.states in the dynamical superlattice. The atoms are loaded into the unit cells of a shallow checkerboard lattice under strongly attractive interactions the experimental sweep of the ratiogates. The shaded background shows the fluctuation in the exchange energy if the tunnelling is changed by ± 10%. The lattice parameters used for the calculation of superexchange interaction are Extended Data Fig. 5 Robustness of geometric SWAP gate under different noise bandwidths and band structure during the pump cycle. Raw fidelity as a function of added tunnelling noise for bandwidths of 2 kHz and 3 kHz . The 2 kHz data is reproduced from Fig.for comparison. The 3 kHz data was measured using an identical protocol, with each point averaged over 10 experimental realisations. The calculated energy spectrum of the three lowest Bloch bands as a function of the superlattice phase. The insets show the Wannier functions for the different energy bands in the staggered and dimerised lattice. The geometric SWAP gate and bidirectional topological pumping operate within the lowest two bands, which are separated by an energy gap of 5.6−8.1 kHz. The third band is separated by a much larger gap , effectively suppressing non-adiabatic excitations.Springer Nature or its licensor holds exclusive rights to this article under a publishing agreement with the author or other rightsholder; author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
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