Research
My research interests focus on theoretical problems related to quantum magnetism, ranging from mesoscopic physics to strongly correlated systems, using a large variety of analytical and cutting-edge numerical methods.
Magnetic Skyrmions
Skyrmion Qubits. We introduce a new class of primitive building blocks for realizing quantum logic elements based on nanoscale magnetization textures called 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. We propose microwave MFGs for skyrmion qubit manipulation and gate operation, and consider skyrmion multiqubit schemes for a scalable architecture. 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. 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.
Quantum Dynamics. Part of my research is related to the quantum propagation of skyrmions in chiral magnets beyond the classical limit. Within the framework I developed along with my collaborators, a detailed origin of dissipation emerges naturally and is linked to the microscopics details. In some limits, the effect of damping is reduced to a mass term, predicted for the first time. We revealed that skyrmions in magnetic insulators can tunnel out of a pinning potential into the classically forbidden region in the experimentally accessible low-temperature regime, and are thus very promising candidates for macroscopic quantum tunneling, one of the most remarkable manifestations of the interplay between quantum and classical mechanics.
Manipulating skyrmions with ac fields. We addressed the problem of a skyrmion propagating under a time-dependent oscillating magnetic field gradient which acts as a net driving force on the skyrmion via its own intrinsic magnetic excitations. We treated the unavoidable impact of the driving field on the magnon bath, which is usually neglected, and demonstrated that new time-dependent dissipation terms arise for the skyrmion, which result in a new type of unidirectional propagation. We addressed the stochastic effects of the quantum driven bath on the skyrmion propagation, and provided a generalized version of the nonequilibrium fluctuation-dissipation relation for externally driven reservoirs. The proposed setup is an ideal experimental platform to test our predictions and to provide new ways of manipulating the skyrmion dynamics. In a recent work we demonstrated that a skyrmion-antiskyrmion bilayer forms a topological charge dipole when excited by in-plane microwave fields, which can act as a spin-wave antenna. We predicted a novel reliable mechanism 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.
Curvature induced effects. Quite recently, we studied the dynamics of magnetic skyrmions on deformable geometries and revealed that novel curvature-driven effects emerge in geometries with non-constant curvature. An inertia term and a pinning potential are generated by the varying curvature, while both of these terms vanish in the flat-space limit.
Quantum and Frustrated Magnetism
Transport in Low Dimensional Quantum Systems. Part of my research interests includes the dynamics and transport properties of antiferromagnetic S = 1 and S = 1/2 chains, with special emphasis on their behavior close to field-induced quantum phase transitions. I have performed a detailed theoretical study of the electron spin resonance spectrum of the S = 1 chain with strong easy plane anisotropy, followed by on-site theoretical support of the experiment that took place at the National High Magnetic field Laboratory in Tallahassee (USA). I have demonstrated that the thermodynamic quantities in one dimension exhibit a characteristic behavior that is a signature of the strong correlations of the system with a characteristic quantum critical scaling non-reproducible by a simple picture of non-interacting magnons. Along with my collaborators, we have conducted detailed studies of the dynamic correlation functions pertinent to the spin and thermal transport of the S = 1 and S = 1/2 model in the presence of finite magnetic fields. Due to the integrability of the S = 1/2 model, we analytically derived the non-decaying long time asymptotic of the thermal and spin conductivity. With our novel input of energy and spin transport, we are able to determine the thermal Seebeck coefficient, a relevant quantity for spintronic applications. Our analysis treats exactly the full problem of quantum transport in a strongly correlated system defined on a discrete lattice for arbitrary values of the magnetic field and temperature and is thus, beyond mean-field or effective low energy theories.
Frustrated Magnetism. My research interests in the thermal transport of quantum spin systems were recently extended in more involved topological models that are known to support quantum spin liquid phases (QSL) and exotic fractional elementary excitations. We identified the fingerprints of a proximate quantum spin-liquid (QSL), observable by finite-temperature dynamical thermal transport, within a minimal version of the idealized Kitaev model on a two-leg ladder, if subjected to inevitable Heisenberg couplings.
Frequency Conversion in Quantum Machines.
The development of efficient frequency conversion mechanisms is a process with various technological applications, relevant for quantum communications and quantum computing. Disparate quantum systems are connected via quantum interfaces, capable of bridging the frequency gap between photonic channels and elementary quantum processors. Temporal analogs of topological models can provide a new platform for the quantized frequency photon conversion, as long as the system is in the near-adiabatic limit realized for sufficiently strong drives. I have recently established a novel photon pumping phenomenon in the experimentally accessible weak-drive regime in a periodically driven spin-1/2 coupled to a quantum cavity mode, with a high photon frequency efficiency, making the experimental observation of this effect feasible. Our work shows that away from the adiabatic limit, the topological properties of the model become less important, making the statistical description of the pumping effect necessary by considering an ensemble of generic Hamiltonians. Thus, we were led to study the energy transfer effect in a random-matrix Floquet Hamiltonian, focusing on the Floquet level statistics and the optimization of the frequency conversion efficiency using Machine Learning algorithms .