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Silvia Viola Kusminskiy

Publications and source records attributed to Silvia Viola Kusminskiy.

At least 19 recordsLinked to original sources
arXiv2026

Chiral magnons for spin-qubit state transfer

We propose a protocol where chiral magnons mediate a state transfer between two distant spin qubits. The protocol is implemented by varying the coupling between the spin qubits and the magnons in time, such that an arbitrary state is transferred from one qubit to the other. The modulation of the coupling is performed such that the two-spin-qubit state is kept as a dark state of the magnon bath, bypassing the associated losses. We show that the protocol can be realized on a hybrid system composed of two nitrogen-vacancy (NV) centers coupled to the nonreciprocal and chiral magnon modes of an yttrium iron garnet (YIG) stripe. We propose two methods to achieve the time modulation of the NV-magnon coupling: i) the NV-magnet distance of both NV centers is varied; ii) the external magnetic field and the NV-magnet distance of one NV center are varied. We evaluate the implementability of both methods numerically, including the constraints on the temperature, and the dephasing time and minimal lifetime of the spin qubits required for high-fidelity state transfer. We find that using realistic experimental parameters, a state transfer between NV centers at a distance of several microns can be achieved with a fidelity $\gtrsim 0.95$. Our findings expand the toolbox of magnonics for quantum information purposes.

quant-ph↗
arXiv2026

Signatures of Topological Magnon Edge States in THz Spectroscopy and Cavity Response

Topological magnon insulators (TMIs) have emerged as promising platforms for low-energy spin-based information processing, due to their non-trivial bulk magnon topology and robust, chiral edge modes that support dissipationless transport. Although theoretical models predict these edge states, direct experimental detection remains challenging due to their limited sensitivity to conventional probes. In this work, we propose an all-optical pathway to detect topological magnon edge modes in ferromagnetic TMIs. Our approach harnesses parametric amplification of edge magnons via resonant electromagnetic driving, enabled by magnetoelectric coupling mechanisms. We concentrate on two-dimensional van der Waals ferromagnetic materials on the honeycomb lattice with magnonic band gaps in the terahertz (THz) range. We show that a spin-dependent effective electric dipole moment, arising from dynamic charge fluctuations and consistent with the lattice symmetry up to next-nearest-neighbor interactions, gives rise to one-photon-two-magnon processes leading to parametric amplification. On this basis, we propose a THz pump-probe spectroscopy protocol in which edge modes are selectively amplified and subsequently detected in absorption. Furthermore, we discuss the possibility of using THz cavities, enabling selective coupling to edge modes while filtering out bulk contributions. These findings establish a route for probing topological magnets and open new avenues for experimental exploration of exotic topological phenomena in magnetic quantum materials.

cond-mat.mes-hall↗
arXiv2026

Steady-state entanglement of spin qubits mediated by nonreciprocal and chiral magnons

We propose a hybrid quantum system in which a magnet supporting non-reciprocal magnons, chiral magnons, or both mediates the dissipative and unidirectional coupling of spin qubits. By driving the qubits, the steady state of this qubit-qubit coupling scheme becomes the maximally entangled Bell state. We devise a protocol where the system converges to this entangled state and benchmark it including qubit decay and dephasing. The protocol is numerically tested on a hybrid system consisting of nitrogen-vacancy (NV) centers coupled to magnon surface modes of an yttrium iron garnet (YIG) film. We show that the dephasing time of the NV centers forms the bottleneck for achieving the entanglement of NV centers separated by a distance within the magnon coherence length. Our findings identify the key technological requirements and demonstrate a viable route toward steady-state entanglement of solid-state spins over distances of several microns using magnonic quantum networks, expanding the toolbox of magnonics for quantum information purposes.

quant-ph↗
arXiv2026

Temperature dependence of the magnon-phonon coupling in yttrium iron garnet/gadolinium gallium garnet high overtone bulk acoustic resonators

Weexperimentally study the temperature dependence of the magnon-phonon coupling in a yttrium iron garnet (YIG)/gadolinium gallium garnet (GGG) heterostructure. More specifically, we use broadband ferromagnetic resonance to investigate the magneto-elastic coupling between the Kittel mode of a YIG thin film and the transverse acoustic phonon modes of the YIG/GGG high overtone bulk acoustic wave acoustic resonator for in and out-of-plane field directions in the temperature range between T = 5K and 300K. We find that for a magnetic field applied normal to the film surface, magneto-elastic coupling decreases with decreasing temperature, whereas it increases for the in-plane magnetic field configuration. The observed temperature dependence differs from earlier observations on bulk YIG samples, which might be due to the temperature dependent stress imposed by the GGG substrate.

cond-mat.mtrl-sci↗
arXiv2026

Magnon-mediated microwave to optical time dynamics

Optomagnonic modulation techniques are an emerging platform for information transfer from the microwave to the optical domain. However, these techniques focus largely on the spectral domain of the transduced signal. Given the potential of the field to bridge the gap between microwave and optical signals, analyzing and studying the interactions real-time in temporal domain becomes equally essential. In this work, we exploit the optomagnonic modulation in a YIG microsphere to demonstrate and study microwave to optical real-time dynamic transfer on a time scale comparable to the decay of magnons. We inductively excite magnons in the microwave domain and use magnon-based Brillouin light scattering to transduce the signature of excited magnonic waveforms to the optical domain. The square type modulation of the magnons is retrieved in the corresponding optical sidebands. Our work enables real-time measurement of the magnonic dynamics and therefore direct access to lifetime measurements of the magnonic mode. Providing insight into the temporal dynamics of magnons, this work can open up new promising research directions such as in magnon coupled superconducting qubits or magnon-based Brillouin memory.

physics.optics↗
arXiv2026

Light-Matter-Coupling formalism for magnons: probing quantum geometry with light

Nontrivial quantum geometry is a key feature of the wavefunctions of collective magnetic excitations in topological systems, but accessing it experimentally remains an open challenge. While Raman circular dichroism (RCD) has emerged as a promising probe, the fundamental link between the RCD and magnon quantum geometry has remained unsettled, and complicated by the fact that magnons are charge neutral. Here, we identify when and why this link exists. We show that, under broad conditions, the Fleury-Loudon Raman vertex can be obtained directly from a light-matter coupling expansion of the effective magnon Hamiltonian, bypassing the conventional microscopic derivation based on virtual electronic processes. This yields an analytical connection between the RCD and the Berry curvature of magnon bands. Applied to monolayer CrI\textsubscript{3}, our theory predicts finite temperature signatures of topological magnons in the RCD. These results establish a general route to quantum-geometry sensitive optical probes in magnonic systems.

cond-mat.mes-hall↗
arXiv2026

Gyroscopically stabilized quantum spin rotors

Recent experiments demonstrate all-electric spinning of levitated nanodiamonds with embedded nitrogen-vacancy spins. Here, we argue that such gyroscopically stabilized spin rotors offer a promising platform for probing and exploiting quantum spin-rotation coupling of particles hosting a single spin degree of freedom. Specifically, we derive the effective Hamiltonian describing how an embedded spin affects the rotation of rapidly revolving quantum rotors due to the Einstein-de Haas and Barnett effects, which we use to devise experimental protocols for observing this coupling in state-of-the-art experiments. This will open the door for future exploitations of quantum spin rotors for superposition experiments with massive objects.

quant-ph↗
arXiv2026

Magnetoelastic conversion in integrated YIG nanostructures

Motivated by the recent proposal of two-step transduction from microwave to optical domain using magnetic and elastic intermediate stages arXiv:2205.05088, we consider the coupling between resonant magnetic and elastic modes within a simple axially-symmetric nanodevice designed to host high-quality-factor acoustic modes: A suspended YIG ring structure supported by a central stem, fabricated from a continuous single-crystal film. We study the modes of the system with our custom finite element solvers. We identify the lowest order ``breathing'' mode of a magnetic vortex and the lowest order elastic breathing mode as having the largest mode overlap. For this pair of modes, the external out-of-plane magnetic bias field is critical for bringing them into resonance; however, we show that at the same time it also affects the strength of the coupling. To counteract this, we optimize the radius of the ring at fixed thickness. For the 100 nm-thick film the resonant coupling is maximized at $g/2π= 8\text{MHz}$ at $R\approx1.7μ\text{m}$, indicating that the overlap integral approaches the idealized limit assumed in previous order-of-magnitude estimates. Our results pave the way for the design of tunable frequency-conversion devices based on magnetoelastics.

cond-mat.mes-hall↗
arXiv2026

Optomagnetic forces on YIG/YFeO3 microspheres levitated in chiral hollow-core photonic crystal fibre

We explore a magnetooptomechanical system consisting of a single magnetic microparticle optically levitated within the core of a helically twisted single-ring hollow-core photonic crystal fibre. We use newly-developed magnetic particles that have a core of antiferromagnetic yttrium-ortho-ferrite (YFeO3) and a shell of ferrimagnetic YIG (Y3Fe5O12) approximately 50 nm thick. Using a 632.8 nm probe beam, we observe optical-torque-induced rotation of the particle and rotation of the magnetization vector in presence of an external static magnetic field. This one-of-a-kind platform opens a path to novel investigations of optomagnetic physics with levitated magnetic particles.

physics.optics↗
arXiv2025

Numerical investigation of electrostatically confined excitons in monolayer $\text{MoSe}_2$

We investigate exciton confinement to a quantum wire in monolayer $\text{MoSe}_2$ where the confinement is achieved by a p-i-n junction. We employ an effective-mass exciton model and solve the problem numerically, reflecting device geometries found in experimental state-of-the-art set up. Our method allows us to investigate the entire spectrum of confined states. We show the emergence of quantum confinement and study the dependence of the confined states as a function of electrical gate voltages, which are experimentally tunable parameters. We find that the confined states can be divided into bright and dark states with the dark states having small but finite oscillator strengths. Their oscillator strengths are low enough that they have not yet been detected in experiments, whereas the spectrum of the bright exciton states reproduces recent experimental measurements. Our results provide insight into the theoretical background of confined exciton states beyond the ground state and pave the way for the development of new confinement schemes as well as avenues to access the previously not detected dark states.

cond-mat.mes-hall↗
arXiv2025

Bosonic quantum error correction with microwave cavities for quantum repeaters

Long-distance quantum communication necessitates the use of quantum repeaters, which typically include highly coherent quantum memories. We provide a theoretical analysis of the secret key rates for a quantum repeater system incorporating bosonic error correction and memory components. Specifically, we focus on the application of Binomial codes for two repeater segments. Using these codes, our investigation aims to suppress memory loss errors that commonly affect systems such as atoms and microwave cavities, in contrast to dephasing errors in single-spin memories. We further discuss a physical implementation of such a quantum repeater comprising a microwave cavity and a superconducting transmon, capable of state engineering with high fidelities ($>97\%$) and logical Bell state measurements for successful entanglement swapping. As an alternative approach, we also discuss a realization in the all-optical domain.

quant-ph↗
arXiv2025

Theory of polarization-dependent phonon pumping in ferromagnetic/non-magnetic bilayers

We develop a theoretical model for polarization-selective phonon pumping induced by magnon-phonon coupling in a ferromagnetic/non-magnetic acoustic bilayer structure, focusing on the effects arising from a misalignment between the magnetic and crystallographic symmetry axes. Our model considers the coupled equations of motion describing uniform magnetization dynamics (the Kittel mode) and elastic waves in both layers, incorporating phonon pumping and boundary conditions at the interface. We show that even small misalignments lift the degeneracy of transverse shear elastic modes, resulting in phononic birefringence characterized by distinct propagation velocities for linearly polarized modes. Furthermore, our analysis reveals that magnon-phonon hybridization gives magnetic-field-dependent properties to otherwise non-magnetic phonons. We show that the polarization transfer between linearly polarized phonons and the circularly polarized Kittel mode can be tuned with an external magnetic field. Our theoretical results quantitatively reproduce recent experimental findings [1].

cond-mat.mes-hall↗
arXiv2024

Quantum Anomalous Hall Effect in $d$-Electron Kagome Systems: Chern Insulating States from Transverse Spin-Orbit Coupling

The possibility of quantum anomalous Hall effect (QAHE) in two-dimensional kagome systems with $d$-orbital electrons is studied within a multi-orbital tight-binding model. We concentrate on the case of isotropic Slater-Koster integrals which is realized in a recently discovered class of metal-organic frameworks TM$_3$C$_6$O$_6$ with transition metals (TM) in the beginning of the 3$d$ series. Furthermore, in the absence of exchange-type spin-orbit coupling, only isotropic Slater-Koster integrals give a perfect flatband in addition to the two dispersive bands hosting relativistic (Dirac) and quadratic band crossing points at high symmetry spots in the Brillouin zone. A quantized topological invariant requires a flux-creating spin-orbit coupling, giving Chern number (per spin sector) $C=1$ not only from the familiar Dirac points at the six corners of the Brillouin zone, but also from the quadratic band crossing point at the center $Γ$. In the case of isotropic Slater-Koster integrals the on-site spin-orbit coupling (SOC) is ineffective to create the QAHE and it is only the transfer or exchange-type SOC which can lead to a QAHE. Surprisingly, this QAHE comes from the nontrivial effective flux induced by the \textit{transverse} part of the spin-orbit coupling, exhibited by electrons in the $d$-orbital state with $m_l=0$ ($d_{z^2}$ orbital), in stark contrast to the more familiar form of QAHE due to the $d$-orbitals with $m_l \neq 0$, driven by the Ising part of spin-orbit coupling. The $C=1$ Chern plateau (per spin sector) due to Dirac point extends over a smaller region of Fermi energy than that due to quadratic band crossing. Our result hints at the promising potential of kagome $d$-electron systems as a platform for dissipationless electronics by virtue of its unique QAHE.

cond-mat.str-el↗
arXiv2024

Cavity-Enhanced Optical Manipulation of Antiferromagnetic Magnon-Pairs

The optical manipulation of magnon states in antiferromagnets (AFMs) holds significant potential for advancing AFM-based computing devices. In particular, two-magnon Raman scattering processes are known to generate entangled magnon-pairs with opposite momenta. We propose to harness the dynamical backaction of a driven optical cavity coupled to these processes, to obtain steady states of squeezed magnon-pairs, represented by squeezed Perelomov coherent states. The system's dynamics can be controlled by the strength and detuning of the optical drive and by the cavity losses. In the limit of a fast (or lossy) cavity, we obtain an effective equation of motion in the Perelomov representation, in terms of a light-induced frequency shift and a collective induced dissipation which sign can be controlled by the detuning of the drive. In the red-detuned regime, a critical power threshold defines a region where magnon-pair operators exhibit squeezing, a resource for quantum information, marked by distinct attractor points. Beyond this threshold, the system evolves to limit cycles of magnon-pairs. In contrast, for resonant and blue detuning regimes, the magnon-pair dynamics exhibit limit cycles and chaotic phases, respectively, for low and high pump powers. Observing strongly squeezed states, auto-oscillating limit cycles, and chaos in this platform presents promising opportunities for future quantum information processing, communication developments, and materials studies.

cond-mat.mes-hall↗
arXiv2024

Magnon-mediated quantum gates for superconducting qubits

We propose a hybrid quantum system consisting of a magnetic particle inductively coupled to two superconducting transmon qubits, where qubit-qubit interactions are mediated via magnons. We show that the system can be tuned into three different regimes of effective qubit-qubit interactions, namely a transverse ($XX + YY$), a longitudinal ($ZZ$) and a non-trivial $ZX$ interaction. In addition, we show that an enhanced coupling can be achieved by employing an ellipsoidal magnet, carrying anisotropic magnetic fluctuations. We propose a scheme for realizing two-qubit gates, and simulate their performance under realistic experimental conditions. We find that iSWAP and CZ gates can be performed in this setup with an average fidelity $\gtrsim 99 \% $ , while an iCNOT gate can be applied with an average fidelity $\gtrsim 88 \%$. Our proposed hybrid circuit architecture offers an alternative platform for realizing two-qubit gates between superconducting qubits and could be employed for constructing qubit networks using magnons as mediators.

quant-ph↗
arXiv2024

Quantum tomography of magnons using Brillouin light scattering

Quantum magnonics, an emerging field focusing on the study of magnons for quantum applications, requires precise measurement methods capable of resolving single magnons. Existing techniques introduce additional dissipation channels and are not apt for magnets in free space. Brillouin light scattering (BLS) is a well-established technique for probing the magnetization known for its high sensitivity and temporal resolution. The coupling between magnons and photons is controlled by a laser input, so it can be switched off when a measurement is not needed. In this article, we theoretically investigate the efficacy of BLS for quantum tomography of magnons. We model a finite optomagnonic waveguide, including the optical noise added by the dielectric, to calculate the signal-to-noise ratio (SNR). We find that the SNR is typically low due to a small magneto-optical coupling; nevertheless, it can be significantly enhanced by injecting squeezed vacuum into the waveguide. We reconstruct the density matrix of the magnons from the statistics of the output photons using a maximum likelihood estimate. The classical component of a magnon state, defined as the regions of positive Wigner function, can be reconstructed with a high accuracy while the non-classical component necessitates either a higher SNR or a larger dataset. The latter requires more compact data structures and advanced algorithms for post-processing. The SNR is limited partially by the input laser power that can be increased by designing the optomagnonic cavity with a heat sink.

quant-ph↗
arXiv2023

Engineering Entangled Coherent States of Magnons and Phonons via a Transmon Qubit

We propose a scheme for generating and controlling entangled coherent states (ECS) of magnons, i.e. the quanta of the collective spin excitations in magnetic systems, or phonons in mechanical resonators. The proposed hybrid circuit architecture comprises a superconducting transmon qubit coupled to a pair of magnonic Yttrium Iron Garnet (YIG) spherical resonators or mechanical beam resonators via flux-mediated interactions. Specifically, the coupling results from the magnetic/mechanical quantum fluctuations modulating the qubit inductor, formed by a superconducting quantum interference device (SQUID). We show that the resulting radiation-pressure interaction of the qubit with each mode, can be employed to generate maximally-entangled states of magnons or phonons. In addition, we numerically demonstrate a protocol for the preparation of magnonic and mechanical Bell states with high fidelity including realistic dissipation mechanisms. Furthermore, we have devised a scheme for reading out the prepared states using standard qubit control and resonator field displacements. Our work demonstrates an alternative platform for quantum information using ECS in hybrid magnonic and mechanical quantum networks.

quant-ph↗
arXiv2023

A Finite-Difference Time-Domain approach for dispersive magnetic media

We extend the Finite-Difference Time-Domain method to treat dispersive magnetic media by incorporating magneto-optical effects through a frequency-dependent permittivity tensor. For benchmarking our method, we consider the light scattering on a magnetic sphere in the Mie regime. We first derive the analytical scattering expressions which predict a peak broadening in the scattering efficiency due to the atomic energy level splitting in the presence of a magnetic field, together with an additional rotated part in the scattered field profile due to the Faraday rotation. We show that our numerical method is able to capture the main scattering features and discuss its limitations and possible improvements in accuracy.

physics.optics↗