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Engineering the dynamics of magnetic skyrmions using non-equilibrium protocols

Periodic Reporting for period 2 - Q-Skyrmions (Engineering the dynamics of magnetic skyrmions using non-equilibrium protocols)

Reporting period: 2021-10-01 to 2022-09-30

This project addresses fundamental aspects of out-of-equilibrium driven magnetic skyrmion dynamics. We utilize the effect of topology on magnetization dynamics to design platforms for the controlled emission of nanoscale spin-waves with tunable characteristics linked to the topology of the source, applicable to a large variety of skyrmion-hosting materials. We study the dynamics of magnetic skyrmions on deformable geometries and reveal that novel curvature-driven effects emerge in geometries with non-constant curvature. While the conventional data storage technology is gradually reaching its limits, skyrmion-based devices hold great promise as a basis for a new type of information technology. To utilize skyrmions in future storage devices, it is necessary to understand and control their response to external fields.

We also design new physical qubits for quantum computing based on topological skyrmions. We construct several qubit archetypes by engineering the potential energy landscape using impurity defects, external fields, geometrical confinement and tailored heterostructures. The logical states can be adjusted by electric and magnetic fields, offering a rich operation regime with high anharmonicity. We propose microwave magnetic field gradients for skyrmion qubit manipulation and gate operation, and consider skyrmion multiqubit schemes for a scalable architecture. Quantum computing holds the promise of improving computer performance, with many applications including material design and drug development. We introduce a new class of qubits based on skyrmions examine a few traditional requirements including the ability to initialize, coherently control and measure the quantum state, as well as long coherence times. Scalability, controllability by microwave fields, operation time scales, and readout by nonvolatile techniques converge to make the skyrmion qubit highly attractive as a logical element of a quantum processor.

Moreover, we consider periodically driven magnetic systems coupled to a quantum cavity as a new platform for the efficient transfer of photons from one electromagnetic mode to another. We explore the frequency conversion problem through optimazation techniques of the corresponding Floquet Hamiltonian using Machine Learning and Deep Learning techniques. The development of efficient frequency conversion mechanisms is a process with various technological applications, relevant for quantum communications and quantum computing and a cornerstone of quantum machines and amplifiers.

We explore new ways to probe and utilize magnetic skyrmion dynamics and examine the extent to which they can enable superior future technologies. Our work addresses fundamental aspects of the skyrmion physics that are especially relevant for applications. We also explore novel functionalities for magnetic skyrmions by considering their dynamics in tailored curved geometries. Our work on skyrmion qubits lies at the intersection of two otherwise disconnected research directions, the field of qubits, aiming to develop a quantum computer, and the field of skyrmionics, intending to design future spintronic devices based on magnetic skyrmions. It introduces an entirely new direction to the former and an unexplored avenue for the latter.
Skyrmion-based spin wave antenna.

We studied the problem of nonequilibrium topological magnetic skyrmion dynamics under an microwave magnetic field and proposed a platform to utilize the effect of topology on magnetization dynamics. We considered a skyrmion-antiskyrmion bilayer in the presence of a in-plane microwave magnetic field which activates the gyrotropic mode of the skyrmion core. Spin waves emitted by the interacting gyrating cores have a preferred propagating direction, with dipole signatures in their radiation pattern, suggesting that the bilayer forms a topological charge dipole, which acts as a spin-wave antenna. Besides being of fundamental interest, skyrmion-antiskyrmion bilayers be used as efficient spin-wave emitters with enriched and controlled characteristics.

Curvature-induced skyrmion mass

We describe the dynamics of a skyrmions propagating on a magnetic surface with nontrivial geometry and demonstrated that spaces with nonconstant curvature generate an effective potential and an inertial term for the skyrmion guiding center, while both of these terms vanish in the flat-space limit. Our investigation suggests that curvature in thin magnetic fields introduces novel ways to tailor the dynamic properties of magnetic topological particles, an effect that we anticipate to be of high importance for nanomagnetism applications.

Skyrmion Qubits

Quantum computing promises to dramatically improve computational power by harnessing the intrinsic properties of quantum mechanics. We introduced a new class of primitive building blocks for realizing quantum logic elements based skyrmions. In a skyrmion qubit, information is stored in the quantum degree of helicity, and the logical states can be adjusted by electric and magnetic fields, offering a rich operation regime with high anharmonicity. By exploring a large parameter space, we propose two skyrmion qubit variants depending on their quantized state. We discuss appropriate microwave pulses required to generate single-qubit gates for quantum computing, and skyrmion multiqubit schemes for a scalable architecture with tailored couplings. We discussed how scale-up multiqubit challenges can be addressed by leveraging state-of-the-art skyrmion technology and show that skyrmion qubits are suitable for quantum computing technology. We calculated the experimental conditions to observe macroscopic quantum phenomena, a precondition for quantum computing.

Photon pumping in a quantum cavity–spin system

We considered the problem of a periodically driven magnetic system coupled to a quantum cavity as a new platform for the efficient transfer of photons from one electromagnetic mode to another. The frequency conversion properties are linked to the delocalization of the corresponding Floquet states which display multifractal behavior as the result of hybridization between localized and delocalized sectors. The quantum coherence properties of the initial state are preserved during the frequency conversion process, as is needed for the bidirectional transfer of quantum information. We propose Random Floquet Hamiltonians as a general framework to investigate frequency conversion effects in a new class of generic dynamical processes beyond adiabatic pumps.
Our work accounts for a real step forward in the field of skyrmionics, which has emerged from the concentrated experimental and theoretical interest on magnetic skyrmions as promising candidates for potential spintronic applications. The novel skyrmion qubit proposal introduces an entirely new direction in the fields of skyrmionics, nanomagnetism and topology and opens an unexplored avenue for quantum computing. The development of a skyrmion qubit will be accelerated by leveraging knowledge and technology from the skyrmionics field, which is directly transferable into into the proposed platform.
I fully anticipate that the scientific achievements of this project will predict novel phenomena and will contribute to advancing the fundamental framework behind a number of future technological applications.