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Integrated optical addressing of an ion qubit


The long coherence times and strong Coulomb interactions afforded by trapped ion qubits have enabled realizations of the necessary primitives for quantum information processing1 and the highest-fidelity quantum operations in any qubit to date2,3,4. Although light delivery to each individual ion in a system is essential for general quantum manipulations and readout, experiments so far have employed optical systems that are cumbersome to scale to even a few tens of qubits5. Here we demonstrate lithographically defined nanophotonic waveguide devices for light routing and ion addressing that are fully integrated within a surface-electrode ion trap chip6. Ion qubits are addressed at multiple locations via focusing grating couplers emitting through openings in the trap electrodes to ions trapped 50 μm above the chip; using this light, we perform quantum coherent operations on the optical qubit transition in individual 88Sr+ ions. The grating focuses the beam to a diffraction-limited spot near the ion position with 2 μm 1/e2 radius along the trap axis, and we measure crosstalk errors between 10–2 and 4 × 10–4 at distances 7.5–15 μm from the beam centre. Owing to the scalability of the planar fabrication technique employed, together with the tight focusing and stable alignment afforded by the integration of the optics within the trap chip, this approach presents a path to creating the optical systems required for large-scale trapped-ion quantum information processing.

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Figure 1: Device layout.
Figure 2: Focusing grating schematic and characterization.
Figure 3: Addressing and coherent manipulation of individual ions.
Figure 4: Crosstalk error characterization.


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We thank I. Chuang for initial discussions of the approach; J. Sun, A. Atabaki, A. Eltony and M. Gutierrez for helpful discussions; the MIT Microsystems Technology Laboratory Staff, the Nanostructures Lab and M. Mondol in particular for help with electron beam lithography; and P. Murphy, J. Porter and C. Thoummaraj for assistance with ion-trap fabrication and packaging. This work was partially funded by NSF program ECCS-1408495. K.K.M. acknowledges support from a DOE Science Graduate Fellowship and the NSF iQuISE IGERT programme.

This work was sponsored by the Assistant Secretary of Defense for Research and Engineering under Air Force Contract No. FA8721-05-C-0002. Opinions, interpretations, conclusions and recommendations are those of the authors and are not necessarily endorsed by the US government.

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K.K.M., R.J.R., J.M.S. and J.C. designed the experiments. K.K.M. designed, fabricated and tested the waveguide devices with supervision from R.J.R. C.D.B., R.M., J.M.S. and J.C. designed and constructed the vacuum apparatus and laser system used for the ion trap device characterization, and K.K.M., J.M.S., and J.C. performed the single ion experiments with the device. K.K.M. prepared the manuscript and all authors reviewed it and discussed the results.

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Correspondence to Karan K. Mehta.

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Mehta, K., Bruzewicz, C., McConnell, R. et al. Integrated optical addressing of an ion qubit. Nature Nanotech 11, 1066–1070 (2016).

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