• Open Access

Opportunities for Long-Range Magnon-Mediated Entanglement of Spin Qubits via On- and Off-Resonant Coupling

Masaya Fukami, Denis R. Candido, David D. Awschalom, and Michael E. Flatté
PRX Quantum 2, 040314 – Published 21 October 2021

Abstract

The ability to manipulate entanglement between multiple spatially separated qubits is essential for quantum-information processing. Although nitrogen-vacancy (NV) centers in diamond provide a promising qubit platform, developing scalable two-qubit gates remains a well-known challenge. To this end, magnon-mediated entanglement proposals have attracted attention due to their long-range spin-coherent propagation. Optimal device geometries and gate protocols of such schemes, however, have yet to be determined. Here we predict strong long-distance (>μm) NV-NV coupling via magnon modes with cooperativities exceeding unity in ferromagnetic bar and waveguide structures. Moreover, we explore and compare on-resonant transduction and off-resonant virtual-magnon exchange protocols, and discuss their suitability for generating or manipulating entangled states at low temperatures (T150mK) under realistic experimental conditions. This work will guide future experiments that aim to entangle spin qubits in solids with magnon excitations.

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  • Received 17 January 2021
  • Revised 6 July 2021
  • Accepted 8 September 2021

DOI:https://doi.org/10.1103/PRXQuantum.2.040314

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.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Masaya Fukami1, Denis R. Candido2, David D. Awschalom1,3, and Michael E. Flatté2,4,*

  • 1Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois, USA
  • 2Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA
  • 3Center for Molecular Engineering and Materials Science Division, Argonne National Lab, Lemont, Illinois, USA
  • 4Department of Applied Physics, Eindhoven University of Technology, Eindhoven, Netherlands

  • *michael_flatte@mailaps.org

Popular Summary

Quantum entanglement is a fundamental resource for quantum-information processing. While nitrogen-vacancy (NV) centers in diamond are promising qubit platforms with high coherence for quantum sensing and quantum communication, quantum computation with NV centers remains challenging due to the difficulty of engineering entangling gates between multiple NV centers. Conventionally, NV-NV entanglement is created either by a technique based on a probabilistic indistinguishable photon detection or the magnetic dipole interaction between NV centers, which limits the NV-NV distance to tens of nanometers. Here, we propose an experimental accessible hybrid quantum system to engineer practical entanglement protocols between NV centers separated by over two microns.

The hybrid quantum system we consider is based on two NV centers placed in proximity to a ferromagnetic bar nanostructure, where the entanglement between them is mediated by the excitation of a quanta of dynamic magnetization oscillations, or magnons. This is achieved by the long-range order of ferromagnetic spins and their natural magnetic interaction to NV centers, as well as the magnon confinement effect under the finite-length magnetic bar structure. Furthermore, we investigate gate protocols suitable for generating NV-NV entanglement in such systems by comparing the entanglement quality of protocols with on- and off-resonant magnon excitations at finite temperatures.

Magnon-mediated entanglement schemes of NV centers over a micron length scale are appealing not only to NV-based quantum computation but also to entanglement-assisted quantum sensing and quantum communication. Our calculations serve as a guide for future experiments that aim to demonstrate these proposals with optimal device geometries and gate protocols.

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Vol. 2, Iss. 4 — October - December 2021

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