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Engineering long spin coherence times of spin–orbit qubits in silicon


Electron-spin qubits have long coherence times suitable for quantum technologies. Spin–orbit coupling promises to greatly improve spin qubit scalability and functionality, allowing qubit coupling via photons, phonons or mutual capacitances, and enabling the realization of engineered hybrid and topological quantum systems. However, despite much recent interest, results to date have yielded short coherence times (from 0.1 to 1 μs). Here we demonstrate ultra-long coherence times of 10 ms for holes where spin–orbit coupling yields quantized total angular momentum. We focus on holes bound to boron acceptors in bulk silicon 28, whose wavefunction symmetry can be controlled through crystal strain, allowing direct control over the longitudinal electric dipole that causes decoherence. The results rival the best electron-spin qubits and are 104 to 105 longer than previous spin–orbit qubits. These results open a pathway to develop new artificial quantum systems and to improve the functionality and scalability of spin-based quantum technologies.

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Fig. 1: Spin states of a hole trapped by a boron ion in silicon.
Fig. 2: Spin-echo spectroscopy in 28Si:B.
Fig. 3: T2H and T1 measurements.
Fig. 4: Dynamical decoupling.

Data availability

The data represented in Figs. 14 are provided with the paper as source data. All other data that support results in this Article are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Code availability

The custom codes that were used for drawing energy level diagrams and fitting are available from the corresponding author upon reasonable request.


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This work was supported by the ARC Centre of Excellence for Quantum Computation and Communication Technology (CE170100012), in part by the US Army Research Office (W911NF-08-1-0527). T.K. acknowledges support from the Tohoku University Graduate Program in Spintronics. J.S. acknowledges support from an ARC DECRA fellowship (DE160101490). M.Y.S. acknowledges a Laureate Fellowship. We thank M. Thewalt for the 28Si sample.

Author information




T.K., J.S. and S.R. designed the experiment. T.K. carried out the experiments (except for X-ray diffraction) and analysed the data, with input from J.S., J.v.d.H., C.C., B.C.J., J.C.M. and S.R.; T.K., J.S. and D.C. carried out the theory calculations. T.K. and J.S. performed the numerical simulation of the strain distribution. W.D.H. carried out the X-ray diffraction analyses. H.R., N.A., P.B. and H.-J.P. supplied the boron-doped 28Si crystal. All authors discussed the results. T.K. wrote the manuscript with contributions from all authors.

Corresponding authors

Correspondence to Takashi Kobayashi or Sven Rogge.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–7 and discussions.

Source data

Source Data Fig. 1

Numerical data used to generate Fig. 1a,b.

Source Data Fig. 2

Numerical data used to generate Fig. 2b,c.

Source Data Fig. 3

Numerical data used to generate Fig. 3.

Source Data Fig. 4

Numerical data used to generate Fig. 4.

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Kobayashi, T., Salfi, J., Chua, C. et al. Engineering long spin coherence times of spin–orbit qubits in silicon. Nat. Mater. 20, 38–42 (2021).

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