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Coherent spin-exchange via a quantum mediator

Nature Nanotechnology volume 12, pages 26–30 (2017)Cite this article

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Abstract

Coherent interactions at a distance provide a powerful tool for quantum simulation and computation. The most common approach to realize an effective long-distance coupling ‘on-chip’ is to use a quantum mediator, as has been demonstrated for superconducting qubits1,2 and trapped ions3. For quantum dot arrays, which combine a high degree of tunability4 with extremely long coherence times5, the experimental demonstration of the time evolution of coherent spin–spin coupling via an intermediary system remains an important outstanding goal6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25. Here, we use a linear triple-quantum-dot array to demonstrate a coherent time evolution of two interacting distant spins via a quantum mediator. The two outer dots are occupied with a single electron spin each, and the spins experience a superexchange interaction through the empty middle dot, which acts as mediator. Using single-shot spin readout26, we measure the coherent time evolution of the spin states on the outer dots and observe a characteristic dependence of the exchange frequency as a function of the detuning between the middle and outer dots. This approach may provide a new route for scaling up spin qubit circuits using quantum dots, and aid in the simulation of materials and molecules with non-nearest-neighbour couplings such as MnO (ref. 27), high-temperature superconductors28 and DNA29. The same superexchange concept can also be applied in cold atom experiments30.

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Figure 1: Linear array of three quantum dots and long-range spin transfer.
Figure 2: Superexchange-driven spin oscillations.
Figure 3: Transition from superexchange to nearest-neighbour exchange.

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Acknowledgements

The authors acknowledge discussions with the members of the Delft spin qubit team and sample fabrication by F.R. Braakman. The authors thank M. Ammerlaan, J. Haanstra, R. Roeleveld, M. Tiggelman and R. Vermeulen for technical support. The authors acknowledge financial support from the Intelligence Advanced Research Projects Activity (IARPA) Multi-Qubit Coherent Operations (MQCO) Program, the Netherlands Organization of Scientific Research (NWO) Graduate Program, the Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellowship for Research Abroad and the Swiss National Science Foundation.

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  1. Timothy Alexander Baart and Takafumi Fujita: These authors contributed equally to this work

Authors and Affiliations

  1. QuTech and Kavli Institute of Nanoscience, TU Delft, GA Delft, 2600, The Netherlands

    Timothy Alexander Baart, Takafumi Fujita & Lieven Mark Koenraad Vandersypen

  2. Solid State Physics Laboratory, ETH Zürich, Zürich, 8093, Switzerland

    Christian Reichl & Werner Wegscheider

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  1. Timothy Alexander Baart
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  2. Takafumi Fujita
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  5. Lieven Mark Koenraad Vandersypen
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Contributions

T.A.B. and T.F. executed the experiment and analysed the data. C.R. and W.W. provided the heterostructure. T.A.B., T.F. and L.M.K.V. contributed to the interpretation of the data, and T.A.B. and L.M.K.V. wrote the paper, with comments from T.F.

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Correspondence to Lieven Mark Koenraad Vandersypen.

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The authors declare no competing financial interests.

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Baart, T., Fujita, T., Reichl, C. et al. Coherent spin-exchange via a quantum mediator. Nature Nanotech 12, 26–30 (2017). https://doi.org/10.1038/nnano.2016.188

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