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Qubit-Qudit Entanglement Transfer in Defect Centers with High-Spin Nuclei

Wolf-Rüdiger Hannes and Guido Burkard

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PRX Quantum 7, 033007 – Published 7 July, 2026

DOI: https://doi.org/10.1103/bwcr-8rz5

Abstract

We propose a scheme for accumulating entanglement between long-lived qudits provided by central nuclear spins of defect centers. Assuming a generic setting, the electron spin of each node acts as the communication qubit and may be entangled with other nodes, e.g., through a spin-photon interface. The generally available Ising component of the hyperfine interaction is shown to facilitate repeated entanglement transfer onto memory qudits of arbitrary dimension d≤2I+1 with I the nuclear spin quantum number. When d is set to an integer power of two, maximal entanglement can be generated deterministically and without intermittent driving of nuclear spins. The scheme is applicable to several candidate systems, including the Ge73 germanium vacancy in diamond.

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Popular Summary

A quantum network (“quantum internet”) requires local storage of quantum information (“quantum memory”), typically embodied by quantum two-level systems (qubits). Quantum memories with more than two distinguishable states (qudits) can store more information and become more strongly entangled among each other, thus boosting the performance of quantum networks. However, it is challenging to generate quantum entanglement between qudits, using qubits as a resource. We propose a solution to this problem for the case of solid-state defect centers featuring high-spin nuclei (e.g., the germanium-73 vacancy in diamond), acting as quantum memory nodes with ultra-long coherence. The electron spins of defects serve as qubits which can be entangled via their interaction with photons. The strong hyperfine coupling can be exploited to repeatedly and rapidly transfer entanglement from the electron spin onto the nuclear spin. The resulting states are an essential ingredient for qudit versions of quantum communication protocols in quantum networks.

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Outline

Information

PRX Quantum 7, 033007– Published 7 July, 2026
  • Received 26 January 2026
  • Revised 5 May 2026
  • Accepted 5 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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