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Nuclear spin quantum register in an optically active semiconductor quantum dot

Abstract

Epitaxial quantum dots (QDs) have long been identified as promising charge spin qubits offering an efficient interface to quantum light and advanced semiconductor nanofabrication technologies. However, charge spin coherence is limited by interaction with the nanoscale ensemble of atomic nuclear spins, which is particularly problematic in strained self-assembled dots. Here, we use strain-free GaAs/AlGaAs QDs, demonstrating a fully functioning two-qubit quantum register using the nanoscale ensemble of arsenic quadrupolar nuclear spins as its hardware. Tailored radio-frequency pulses allow quantum state storage for up to 20 ms, and are used for few-microsecond single-qubit and two-qubit control gates with fidelities exceeding 97%. Combining long coherence and high-fidelity control with optical initialization and readout, we implement benchmark quantum computations such as Grover’s search and the Deutsch–Jozsa algorithm. Our results identify QD nuclei as a potential quantum information resource, which can complement charge spins and light particles in future QD circuits.

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Fig. 1: QD nuclear spin register design and characterization.
Fig. 2: Experimental QST of the nuclear spin two-qubit register.
Fig. 3: Experimental quantum computing on the nuclear spin two-qubit register.
Fig. 4: Control fidelity and coherence of the nuclear spin two-qubit register.

Data availability

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

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Acknowledgements

We are grateful to I. Griffiths, C. McEwan and H. Penney for their assistance. E.A.C. was supported by a Royal Society University Research Fellowship and experimental costs were part-funded through EPSRC grant no. EP/N031776/1. Computational resources were in part provided by HPC Iceberg at the University of Sheffield. For sample fabrication and precharacterization, this work was supported by the Austrian Science Fund (FWF), grant no. P29603, the Linz Institute of Technology (LIT) and the LIT Laboratory for secure and correct systems, financed by the State of Upper Austria.

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S.F.C.S. and A.R. developed and grew the QD samples. E.A.C. designed and conducted experiments, analysed the data, performed numerical simulations and coordinated the project. E.A.C. drafted the manuscript with input from S.F.C.S. and A.R.

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Correspondence to Evgeny A. Chekhovich.

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Chekhovich, E.A., da Silva, S.F.C. & Rastelli, A. Nuclear spin quantum register in an optically active semiconductor quantum dot. Nat. Nanotechnol. 15, 999–1004 (2020). https://doi.org/10.1038/s41565-020-0769-3

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