# Single-qubit quantum memory exceeding ten-minute coherence time

## Abstract

A long-time quantum memory capable of storing and measuring quantum information at the single-qubit level is an essential ingredient for practical quantum computation and communication1,2. Currently, the coherence time of a single qubit is limited to less than 1 min, as demonstrated in trapped ion systems3,4,5, although much longer coherence times have been reported in ensembles of trapped ions6,7 and nuclear spins of ionized donors8,9. Here, we report the observation of a coherence time of over 10 min for a single qubit in a 171Yb+ ion sympathetically cooled by a 138Ba+ ion in the same Paul trap, which eliminates the problem of qubit-detection inefficiency from heating of the qubit ion10,11. We also apply a few thousand dynamical decoupling pulses to suppress ambient noise from magnetic-field fluctuation﻿s ﻿and phase noise from ﻿the local os﻿cillator8,9,12,13,14,15,16. The long-time quantum memory of the single trapped ion qubit would be the essential component of scalable quantum computers1,17,18, quantum networks2,19,20 and quantum money21,22.

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## Change history

• ### 12 January 2018

In the version of this Letter originally published, in Fig. 2c legend, the entry ‘LO phase noise’ should not have been included. This has now been corrected in the online versions.

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## Acknowledgements

This work was supported by the National Key Research and Development Program of China under grant 2016YFA0301900 (no. 2016YFA0301901) and the National Natural Science Foundation of China grants 11374178, 11504197 and 11574002.

## Author information

Authors

### Contributions

Y.W. and D.Y. developed the experimental system. Y.W., with the participation of M.U. and D.Y., collected and analysed the data. J.Z. and S.A. provided technical support. M.L., J.-N.Z., L.-M.D. and D.Y. provided theoretical support. K.K. supervised the project. All authors contributed to writing the manuscript.

### Corresponding authors

Correspondence to Dahyun Yum or Kihwan Kim.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

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Reprints and Permissions

Wang, Y., Um, M., Zhang, J. et al. Single-qubit quantum memory exceeding ten-minute coherence time. Nature Photon 11, 646–650 (2017). https://doi.org/10.1038/s41566-017-0007-1

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