Quantum gates and memory using microwave-dressed states


Trapped atomic ions have been used successfully to demonstrate1 basic elements of universal quantum information processing. Nevertheless, scaling up such methods to achieve large-scale, universal quantum information processing (or more specialized quantum simulations2,3,4,5) remains challenging. The use of easily controllable and stable microwave sources, rather than complex laser systems6,7, could remove obstacles to scalability. However, the microwave approach has drawbacks: it involves the use of magnetic-field-sensitive states, which shorten coherence times considerably, and requires large, stable magnetic field gradients. Here we show how to overcome both problems by using stationary atomic quantum states as qubits that are induced by microwave fields (that is, by dressing magnetic-field-sensitive states with microwave fields). This permits fast quantum logic, even in the presence of a small (effective) Lamb–Dicke parameter (and, therefore, moderate magnetic field gradients). We experimentally demonstrate the basic building blocks of this scheme, showing that the dressed states are long lived and that coherence times are increased by more than two orders of magnitude relative to those of bare magnetic-field-sensitive states. This improves the prospects of microwave-driven ion trap quantum information processing, and offers a route to extending coherence times in all systems that suffer from magnetic noise, such as neutral atoms, nitrogen-vacancy centres, quantum dots or circuit quantum electrodynamic systems.

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Figure 1: Microwave-dressed qubit states.
Figure 2: Lifetime of the dressed state | D 〉.
Figure 3: Single-qubit gates with dressed states.
Figure 4: Multiqubit scheme for three ions exposed to a magnetic field gradient.


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Technical help with the microwave set-up by T. F. Gloger is acknowledged. We acknowledge support by the Bundesministerium für Bildung und Forschung (FK 01BQ1012 and P3352014), the Deutsche Forschungsgemeinschaft, the European Commission under the STREP PICC, the German-Israeli Foundation, secunet AG and the Alexander von Humboldt Foundation.

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N.T., I.B., M.J., A.F.V. and Ch.W. contributed to the experiment, the analysis of experimental and theoretical results, and the writing of the manuscript. A.R. and M.B.P. contributed to the theory, the analysis of theoretical and experimental results, and the writing of the manuscript. A.R. and Ch.W. had the idea for theory and experiment.

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Correspondence to A. Retzker or Ch. Wunderlich.

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The authors declare no competing financial interests.

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Timoney, N., Baumgart, I., Johanning, M. et al. Quantum gates and memory using microwave-dressed states. Nature 476, 185–188 (2011). https://doi.org/10.1038/nature10319

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