Multi-element logic gates for trapped-ion qubits


Precision control over hybrid physical systems at the quantum level is important for the realization of many quantum-based technologies. In the field of quantum information processing (QIP) and quantum networking, various proposals discuss the possibility of hybrid architectures1 where specific tasks are delegated to the most suitable subsystem. For example, in quantum networks, it may be advantageous to transfer information from a subsystem that has good memory properties to another subsystem that is more efficient at transporting information between nodes in the network. For trapped ions, a hybrid system formed of different species introduces extra degrees of freedom that can be exploited to expand and refine the control of the system. Ions of different elements have previously been used in QIP experiments for sympathetic cooling2, creation of entanglement through dissipation3, and quantum non-demolition measurement of one species with another4. Here we demonstrate an entangling quantum gate between ions of different elements which can serve as an important building block of QIP, quantum networking, precision spectroscopy, metrology, and quantum simulation. A geometric phase gate between a 9Be+ ion and a 25Mg+ ion is realized through an effective spin–spin interaction generated by state-dependent forces induced with laser beams5,6,7,8,9. Combined with single-qubit gates and same-species entangling gates, this mixed-element entangling gate provides a complete set of gates over such a hybrid system for universal QIP10,11,12. Using a sequence of such gates, we demonstrate a CNOT (controlled-NOT) gate and a SWAP gate13. We further demonstrate the robustness of these gates against thermal excitation and show improved detection in quantum logic spectroscopy14. We also observe a strong violation of a CHSH (Clauser–Horne–Shimony–Holt)-type Bell inequality15 on entangled states composed of different ion species.

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Figure 1: Configuration of laser beams for the mixed-element entangling gate.
Figure 2: Pulse sequences for logic gates.
Figure 3: Robustness of quantum logic readout against thermal excitation.
Figure 4: Ramsey experiments with SWAP gate.


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We thank J. Bollinger and D. Hume for comments on the manuscript. This work was supported by the Office of the Director of National Intelligence (ODNI) Intelligence Advanced Research Projects Activity (IARPA), ONR, and the NIST Quantum Information Program. Y.W. was supported by the US Army Research Office through MURI grant W911NF-11-1-0400. This paper is a contribution by NIST and not subject to US copyright.

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T.R.T. and J.P.G. conceived and designed the experiments, developed components of the experimental apparatus, and collected and analysed data. T.R.T. wrote the manuscript. Y.L., Y.W., and R.B. contributed to the development of experimental apparatus. D.L. and D.J.W. directed the experiment. All authors provided important suggestions for the experiments, discussed the results, and contributed to the editing of the manuscript.

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Tan, T., Gaebler, J., Lin, Y. et al. Multi-element logic gates for trapped-ion qubits. Nature 528, 380–383 (2015).

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