Microwave quantum logic gates for trapped ions


Control over physical systems at the quantum level is important in fields as diverse as metrology, information processing, simulation and chemistry. For trapped atomic ions, the quantized motional and internal degrees of freedom can be coherently manipulated with laser light1,2. Similar control is difficult to achieve with radio-frequency or microwave radiation: the essential coupling between internal degrees of freedom and motion requires significant field changes over the extent of the atoms’ motion2,3, but such changes are negligible at these frequencies for freely propagating fields. An exception is in the near field of microwave currents in structures smaller than the free-space wavelength4,5, where stronger gradients can be generated. Here we first manipulate coherently (on timescales of 20 nanoseconds) the internal quantum states of ions held in a microfabricated trap. The controlling magnetic fields are generated by microwave currents in electrodes that are integrated into the trap structure. We also generate entanglement between the internal degrees of freedom of two atoms with a gate operation4,6,7,8 suitable for general quantum computation9; the entangled state has a fidelity of 0.76(3), where the uncertainty denotes standard error of the mean. Our approach, which involves integrating the quantum control mechanism into the trapping device in a scalable manner, could be applied to quantum information processing4, simulation5,10 and spectroscopy3,11.

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Figure 1: Central portion of the surface-electrode trap.
Figure 2: Level scheme of 25 Mg + (nuclear spin, I = 5/2) and spectroscopy of the qubit transition.
Figure 3: Microwave motional sideband transitions.
Figure 4: Populations and parity of the entangled state.


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We thank M. J. Biercuk, J. J. Bollinger and A. P. VanDevender for experimental assistance, J. C. Bergquist, C. W. Chou and T. Rosenband for the loan of a fibre laser, R. Jordens and E. Knill for comments on the manuscript, and D. Hanneke and J. P. Home for discussions. We thank P. Treutlein for discussions on microfabrication techniques. This work was supported by IARPA, the ONR, DARPA, the NSA, Sandia National Laboratories and the NIST Quantum Information Program. This paper, a submission of NIST, is not subject to US copyright.

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C.O. participated in the design of the experiment and built the experimental apparatus, collected data, analysed results and wrote the manuscript. U.W. participated in building the experimental apparatus, collected data and analysed results. Y.C. developed chip fabrication methods and fabricated the ion trap chip. K.R.B. participated in the design of the experiment, developed chip fabrication methods and helped build parts of the experiment. J.M.A. developed chip fabrication methods and automated experiment control and data taking. D.L. participated in the design of the experiment, collected data and maintained the laser systems. D.J.W. participated in the design and analysis of the experiment. All authors discussed the results and the text of the manuscript.

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Correspondence to C. Ospelkaus.

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Ospelkaus, C., Warring, U., Colombe, Y. et al. Microwave quantum logic gates for trapped ions. Nature 476, 181–184 (2011). https://doi.org/10.1038/nature10290

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