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Advanced Quantum Technologies

Magnon‐Mediated Long‐Range Entanglement in a Spin‐1/2 Heisenberg Chain Coupled to Magnetic Skyrmions

Marius Melz, Jamal Berakdar

Published Feb 1, 2026• 0 citations
Publisher

Abstract

ABSTRACT Magnetic skyrmionic stray fields are functionalizable to trigger, maintain, and steer quantum entanglement in a coupled chain of localized spins. This is demonstrated by an exact‐diagonalization‐based study of the ground state and non‐equilibrium entanglement dynamics. The topology of the magnetic skyrmion is shown to be an essential ingredient. Ground state analysis of spins that are coupled locally to a skyrmionic texture and a global bias magnetic field reveals the existence of strongly and weakly entangled quantum phases with the entanglement being confined to the center of the magnetic texture. For quantum signal transmission, the entanglement dynamics of a magnonic excitation injected at one end of the quantum spin chain is obtained. Scattering is found to generate additional entanglement that is externally controllable by skyrmion and bias fields. In particular, the results illustrate a strong amplification of transmission of correlations by a pre‐entangled initial state. The analysis uncovers the possibility of a resonator setup of two skyrmionic textures which is capable of generating a long‐range entangled steady state after a single injected magnon is scattered by the textures. The findings point to the potential of classical non‐trivial magnetic textures as a generator and driver for quantum entanglement.

DOI
10.1002/qute.202500869

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ABSTRACT Magnetic skyrmionic stray fields are functionalizable to trigger, maintain, and steer quantum entanglement in a coupled chain of localized spins. This is demonstrated by an exact‐diagonalization‐based study of the ground state and non‐equilibrium entanglement dynamics. The topology of the magnetic skyrmion is shown to be an essential ingredient. Ground state analysis of spins that are coupled locally to a skyrmionic texture and a global bias magnetic field reveals the existence of strongly and weakly entangled quantum phases with the entanglement being confined to the center of the magnetic texture. For quantum signal transmission, the entanglement dynamics of a magnonic excitation injected at one end of the quantum spin chain is obtained. Scattering is found to generate additional entanglement that is externally controllable by skyrmion and bias fields. In particular, the results illustrate a strong amplification of transmission of correlations by a pre‐entangled initial state. The analysis uncovers the possibility of a resonator setup of two skyrmionic textures which is capable of generating a long‐range entangled steady state after a single injected magnon is scattered by the textures. The findings point to the potential of classical non‐trivial magnetic textures as a generator and driver for quantum entanglement.
Several recent experiments have shown that long-range exchange interactions can determine collective magnetic ground states of nanostructures in bulk and on surfaces. The ability to generate and control entanglement in a system with long-range interaction will be of great importance for future quantum technology. An important step forward to reach this goal is the creation of entangled states for spins of distant magnetic atoms. Herein, the generation of long-distance entanglement between remote spins at large separations in bulk and on surface is studied theoretically, based on a quantum spin Hamiltonian and time-dependent Schrödinger equation for experimentally realized conditions. We demonstrate that long-distance entanglement can be generated between remote spins by using an appropriate quantum spin chain (a quantum mediator), composed by sets of antiferromagnetically coupled spin dimers. Ground state properties and quantum spin dynamics of entangled atoms are studied. We demonstrate that one can increase or suppress entanglement by adding a single spin in the mediator. The obtained result is explained by monogamy property of entanglement distribution inside a quantum spin system. We present a novel approach for non-local sensing of remote magnetic adatoms via spin entanglement.
We show that the ground state of the Heisenberg spin-1/2 chain in an external magnetic field, can be exactly expressed as a matrix product state, provided that the coupling constants are constrained to be on a specific two dimensional surface. This ground state has a very interesting property: all the pairs of spins are equally entangled with each other. In this last respect, the results are of interest for engineering long-range entanglement in experimentally realizable finite arrays of qubits, where the ground state will act as the initial state of a quantum computer.
We present how entanglement between a spatially separated pair of color centers can be created by letting them weakly interact with the quantum fluctuations of a nonequilibrium magnetic environment. To this end, we consider two coupled ferromagnets, one in the ground state and one in an inverted state with respect to an applied magnetic field. The resulting energetic instability leads to a quantum spin current in the vacuum state that is sustained by the creation of magnon-antimagnon pairs at the interface. We show that these quantum fluctuations imprint a steady-state entanglement onto the two dipole-coupled color centers through nonlocal dissipation. We derive conditions for establishing a maximally entangled Bell state. This entanglement is absent in thermal equilibrium.
The entanglement of many localized spins (LSs) within solid magnetic materials is a topic of great basic and applied interest, particularly after becoming amenable to experimental scrutiny where recent neutron scattering experiments have witnessed macroscopic entanglement in the ground state (GS) of antiferromagnets persisting even at elevated temperatures. On the other hand, spintronics and magnonics studies assume that LSs of antiferromagnets are in unentangled N\'eel GS, as well as that they evolve, when pushed out of equilibrium by current or external fields, according to the Landau-Lifshitz-Gilbert (LLG) equation viewing LSs as classical vectors of fixed length. The prerequisite for applicability of the LLG equation is zero entanglement in the underlying many-body quantum state of LSs. In this study, we initialize quantum Heisenberg ferro- or antiferromagnetic chains hosting S=1/2,S=1S=1/2, S=1S=1/2,S=1, or S=5/2S=5/2S=5/2 LSs into an unentangled pure state and then evolve them by quantum master equations (QMEs) of Lindblad or non-Markovian type, derived by coupling LSs weakly to a bosonic bath (due to phonons in real materials) or by using additional ``reaction coordinate'' in the latter case. The time evolution is initiated by applying an external magnetic field, and entanglement of the ensuing mixed quantum states is monitored by computing its negativity. We find that non-Markovian dynamics never brings entanglement to zero, in the presence of which the vector of spin expectation value changes its length to render the LLG equation inapplicable. Conversely, Lindbladian (i.e., Markovian) dynamics ensures that entanglement goes to 0, thereby enabling quantum-to-classical transition in all cases---S=1/2,S=1S=1/2, S=1S=1/2,S=1, and S=5/2S=5/2S=5/2 ferromagnets or S=5/2S=5/2S=5/2 antiferromagnets---except for S=1/2S=1/2S=1/2 and S=1S=1S=1 antiferromagnets. Finally, we investigate the stability of an entangled antiferromagnetic GS upon suddenly coupling it to bosonic baths.
Abstract We theoretically demonstrate that multipartite entanglement and one-way Einstein–Podolsky–Rosen (EPR) steering in a magnon frequency comb (MFC) can be generated in a hybrid magnon–skyrmion system. When the system is driven by two microwave fields at the magnonic whispering gallery mode (mWGM) and the skyrmion, the skyrmion can be simultaneously entangled with three magnon modes of the MFC and the entanglement of the first-order magnon pair in the MFC also appears. The results show that the perfect one-way steering between the skyrmion and the three magnons can be obtained. Interestingly, the steering direction can be manipulated by controlling the amplitudes of two drive fields, which provides flexibility in controlling the asymmetry of the EPR steering and may well have practical applications. Moreover, the genuine tripartite entanglement among the skyrmion and the first-order magnon pair can be achieved with appropriate parameters in the steady state. Our work exhibits that the MFC has great potential in preparing multi-mode entanglement resources, with promising applications in quantum communication.
The entanglement dynamics between two end spins in an anisotropic spin-1/2 Heisenberg chain is investigated when the external magnetic field and the nearest-neighbor coupling are periodically modulated.The entanglement resonance occurs at certain modulation frequency and magnitude of the external magnetic filed.The maximum entanglement appears only at some specific frequencies while it can keep the maximum for quite broad range of the magnitude.Thus,the entanglement can be controlled by the external magnetic field.