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# Stern–Gerlach detection of neutral-atom qubits in a state-dependent optical lattice

## Abstract

Qubit state measurements are an essential part of any quantum computer, constituting the readout. Accurate measurements are also an integral component of one-way quantum computation and of error correction, which is needed for fault-tolerant quantum computation1. Here, we present a state measurement for neutral-atom qubits based on coherent spatial splitting of the atoms’ wavefunctions. It is reminiscent of the Stern–Gerlach experiment2, but carried out in light traps. For around 160 qubits in a three-dimensional array, we achieve a measurement fidelity of 0.9994, which is roughly 20 times lower error than in previous measurements of neutral-atom arrays3,4. It also greatly exceeds the measurement fidelity of other arrays with more than four qubits, including those with ion and superconducting qubits5,6. Our measurement fidelity is essentially independent of the number of qubits measured, and since the measurement causes no loss, we can reuse the atoms. We also demonstrate that we can replace atoms lost to background gas collisions during the experiment7.

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## Data availability

The data that support the plots in this paper are available from the corresponding author upon reasonable request.

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## Acknowledgements

This work was supported by US National Science Foundation grant numbers PHY-1520976 and PHY-1820849.

## Author information

Authors

### Contributions

All authors contributed to the design, execution and analysis of the experiment and the writing of the manuscript. A.K., T.-Y.W. and F.G. collected all the data.

### Corresponding author

Correspondence to David S. Weiss.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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## Supplementary information

### Supplementary Information

Supplementary Text and Supplementary Figures 1–3.

## Rights and permissions

Reprints and Permissions

Wu, TY., Kumar, A., Giraldo, F. et al. Stern–Gerlach detection of neutral-atom qubits in a state-dependent optical lattice. Nat. Phys. 15, 538–542 (2019). https://doi.org/10.1038/s41567-019-0478-8

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• DOI: https://doi.org/10.1038/s41567-019-0478-8

• ### A quantum processor based on coherent transport of entangled atom arrays

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• Justin E. Christensen
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