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Quantum control of a cat qubit with bit-flip times exceeding ten seconds

An Author Correction to this article was published on 17 May 2024

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Abstract

Quantum bits (qubits) are prone to several types of error as the result of uncontrolled interactions with their environment. Common strategies to correct these errors are based on architectures of qubits involving daunting hardware overheads1. One possible solution is to build qubits that are inherently protected against certain types of error, so the overhead required to correct the remaining errors is greatly reduced2,3,4,5,6,7. However, this strategy relies on one condition: any quantum manipulations of the qubit must not break the protection that has been so carefully engineered5,8. A type of qubit known as a cat qubit is encoded in the manifold of metastable states of a quantum dynamical system, and thereby acquires continuous and autonomous protection against bit-flips. Here, in a superconducting-circuit experiment, we implemented a cat qubit with bit-flip times exceeding 10 s. This is an improvement of four orders of magnitude over previously published cat-qubit implementations. We prepared and imaged quantum superposition states, and measured phase-flip times greater than 490 ns. Most importantly, we controlled the phase of these quantum superpositions without breaking the bit-flip protection. This experiment demonstrates the compatibility of quantum control and inherent bit-flip protection at an unprecedented level, showing the viability of these dynamical qubits for future quantum technologies.

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Fig. 1: Encoding quantum information in a bistable dynamical system.
Fig. 2: Quantum tomography protocol based on the holonomic gate24.
Fig. 3: Cat-qubit phase-flip and bit-flip time measurements.
Fig. 4: Quantum control that preserves bit-flip protection.

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Data availability

The data that support the findings of this work are available from the corresponding author upon reasonable request.

Code availability

The code used for data acquisition, analysis and visualization is available from the corresponding author upon reasonable request.

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Acknowledgements

We thank N. Frattini for his help applying a previously published protocol24 to Wigner tomography, and the SPEC at CEA Saclay for providing nanofabrication facilities. This work was supported by the QuantERA grant QuCOS and ANR 19-QUAN-0006-04. This project has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreements 851740 and 884762); grants ANR-22-PETQ-0003 and ANR-22-PETQ-0006 under the France 2030 plan; and is partly funded by the CATQUBIT Horizon Europe project (grant agreement 190110172).

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Contributions

P.C.-I., R.L., S.J. and Z.L. conceived the experiment. U.R. and A.B. designed the chip with support from M.H. and F.R. U.R. and A.B. measured the device and analysed the data. E.A. and N.P. fabricated the chip. R.G., J.C., A.M., L.-A.S., P.R., A.S. and M.M. provided theory support. U.R., A.B. and Z.L. wrote the paper with input from all authors.

Corresponding author

Correspondence to Z. Leghtas.

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Competing interests

Authors affiliated with Alice & Bob have financial interests in the company. Z.L., M.M. and P.C.-I. are shareholders of Alice & Bob. P.C.-I. is a part-time employee of Alice & Bob.

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Supplementary information sections 1–8. 

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Réglade, U., Bocquet, A., Gautier, R. et al. Quantum control of a cat qubit with bit-flip times exceeding ten seconds. Nature 629, 778–783 (2024). https://doi.org/10.1038/s41586-024-07294-3

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