To advance quantum information science, physical systems are sought that meet the stringent requirements for creating and preserving quantum entanglement. In atomic physics, robust two-qubit entanglement is typically achieved by strong, long-range interactions in the form of either Coulomb interactions between ions or dipolar interactions between Rydberg atoms1,2,3,4. Although such interactions allow fast quantum gates, the interacting atoms must overcome the associated coupling to the environment and cross-talk among qubits5,6,7,8. Local interactions, such as those requiring substantial wavefunction overlap, can alleviate these detrimental effects; however, such interactions present a new challenge: to distribute entanglement, qubits must be transported, merged for interaction, and then isolated for storage and subsequent operations. Here we show how, using a mobile optical tweezer, it is possible to prepare and locally entangle two ultracold neutral atoms, and then separate them while preserving their entanglement9,10,11. Ground-state neutral atom experiments have measured dynamics consistent with spin entanglement10,12,13, and have detected entanglement with macroscopic observables14,15; we are now able to demonstrate position-resolved two-particle coherence via application of a local gradient and parity measurements1. This new entanglement-verification protocol could be applied to arbitrary spin-entangled states of spatially separated atoms16,17. The local entangling operation is achieved via spin-exchange interactions9,10,11, and quantum tunnelling is used to combine and separate atoms. These techniques provide a framework for dynamically entangling remote qubits via local operations within a large-scale quantum register.
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This work was supported by the David and Lucile Packard Foundation and the National Science Foundation under grant number 1125844. C.A.R. acknowledges support from the Clare Boothe Luce Foundation. M.L.W. and A.M.R. acknowledge funding from NSF-PIF, ARO, ARO-DARPA-OLE and AFOSR. M.L.W. and M.F.-F. acknowledge support from the NRC postdoctoral fellowship program.
The authors declare no competing financial interests.
Extended data figures and tables
Extended Data Figure 1 Adiabatic energy eigenstates E as a function of the double-well bias Δ in units of the ground-excited tunnelling Jeg.
At large positive bias, the triplet and singlet eigenstates corresponding to two particles in the same well are split by Jex. The dashed and solid lines denote the energies of the states that asymptotically connect to the states labelled in the figure through the AP process. See Methods for details.
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Kaufman, A., Lester, B., Foss-Feig, M. et al. Entangling two transportable neutral atoms via local spin exchange. Nature 527, 208–211 (2015). https://doi.org/10.1038/nature16073
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