Abstract
Electron charge qubits are compelling candidates for solid-state quantum computing because of their inherent simplicity in qubit design, fabrication, control and readout. However, electron charge qubits built on conventional semiconductors and superconductors suffer from severe charge noise that limits their coherence time to the order of one microsecond. Here we report electron charge qubits that exceed this limit, based on isolated single electrons trapped on an ultraclean solid neon surface in a vacuum. Quantum information is encoded in the motional states of an electron that is strongly coupled with microwave photons in an on-chip superconducting resonator. The measured relaxation and coherence times are both on the order of 0.1 ms, surpassing all existing charge qubits and rivalling state-of-the-art superconducting transmon qubits. The simultaneous strong coupling of two qubits with a common resonator is also demonstrated, as the first step towards two-qubit entangling gates for universal quantum computing.
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The data that support the findings of this study are available from the corresponding authors upon request. Source data are provided with this paper.
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The codes used to perform the experiments and to analyse the data in this work are available from the corresponding authors upon request.
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Acknowledgements
Work performed at the Center for Nanoscale Materials, a US Department of Energy (DOE), Office of Science User Facility, was supported by the US DOE, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. D.J., X.H., X.L. and Q.C. acknowledge support from the Argonne National Laboratory Directed Research and Development (LDRD). D.J. and X. Zhou acknowledge support from the Julian Schwinger Foundation for Physics Research. This work was partially supported by the University of Chicago Materials Research Science and Engineering Center, which is funded by the National Science Foundation under award no. DMR-2011854. This work made use of the Pritzker Nanofabrication Facility of the Institute for Molecular Engineering at the University of Chicago, which receives support from SHyNE, a node of the National Science Foundation National Nanotechnology Coordinated Infrastructure (NSF NNCI-1542205). D.I.S. and B.D. acknowledge support from the National Science Foundation DMR grant DMR-1906003. D.I.S. and C.S.W. acknowledge support from Q-NEXT, one of the US DOE Office of Science National Quantum Information Science Research Centers. G.Y. acknowledges support from the National Science Foundation under Cooperative Agreement PHY-2019786 (the NSF AI Institute for Artificial Intelligence and Fundamental Interactions). X. Zhang acknowledges support from ONR YIP (N00014-23-1-2144). D.J. thanks A. J. Leggett for inspiring discussions. The qubit manipulation and measurement in this work utilized the highly efficient and effective OPX+, Octave and QDAC-II made by Quantum Machines and QDevil.
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X. Zhou, X.L. and D.J. devised the experiment and wrote the manuscript. X. Zhou and X.L. performed the experiment. Q.C. performed the calculations. G.K., G.Y. and D.I.S. designed the device. X.L., G.K., G.Y. and Y.H. fabricated the device. B.D. simulated the device. X. Zhou, X.L., X.H., X. Zhang and D.J. built the experimental setup. C.S.W. and D.I.S. advised the measurement and revised the manuscript. D.J. conceived the idea and led the project. All authors contributed to the manuscript.
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Extended data
Extended Data Fig. 1 Qubit-resonator coupled spectrum, ac Stark shift, and dispersive shift.
a, Schematic of the qubit-resonator coupled spectrum. ωq = 2πfq is the bare qubit frequency, ωr = 2πfr is the bare resonator frequency, and g is the coupling strength. In the resonant regime, fr = fq, the qubit and resonator hybridize and a vacuum Rabi splitting 2g opens up. In the dispersive regime, the detuning ∣Δ = ωq − ωr∣ ≫ g, the actual qubit frequency exhibits the dispersive shift χ and the ac Stark shift \(2\chi \bar{n}\), in which \(\bar{n}\) is the average intra-resonator photon number, whereas the actual resonator frequency exhibits a + χ or − χ shift, when the qubit is kept in the excited or ground state, respectively. b, Observation of the ac Stark shift. The transmission phase ϕ at fp = fr is plotted versus fd and probe power Pp, when the qubit is on the sweet spot in Fig. 1d. With increasing Pp, the qubit frequency is red-shifted because of the ac Stark effect. In the inset, the frequency shift δfac shows a linear dependence on Pp (equivalent to the average intra-resonator photon number \(\bar{n}\)). c, Measurement of the state-dependent dispersive shift. Normalized transmission amplitude \({(A/{A}_{0})}^{2}\) (top) and phase ϕ (bottom) are plotted versus the probe frequency fp when the qubit is in the ground state \(\left\vert 0\right\rangle\) or excited state \(\left\vert 1\right\rangle\). The grey line corresponds to fp = fr, where fr is the bare resonator frequency. The measured dispersive shift is χ/2π = − 0.13 MHz.
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Source Data Extended Data Fig. 1
Numerical source data for Extended Fig. 1.
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Zhou, X., Li, X., Chen, Q. et al. Electron charge qubit with 0.1 millisecond coherence time. Nat. Phys. 20, 116–122 (2024). https://doi.org/10.1038/s41567-023-02247-5
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DOI: https://doi.org/10.1038/s41567-023-02247-5
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