arXiv subjects

Yaroslav Tserkovnyak

Publications and source records attributed to Yaroslav Tserkovnyak.

At least 19 recordsLinked to original sources

arXiv2026

Generating single- and many-body quantum magnonic states

The growing interest in quantum magnonics is driving the development of advanced techniques for generating, controlling, and detecting non-classical magnonic states. Here, we explore the potential of an ensemble of solid-state spin defects coupled to a shared magnetic bath as a source of such states. We establish a theoretical framework to characterize the quantum correlations among magnons emitted by the ensemble into the bath and investigate how these correlations depend on experimentally tunable parameters. Our findings show that the emitted magnons retain the quantum correlations inherent to the solid-state emitters, paving the way for the deterministic generation of quantum many-body magnonic states.

cond-mat.mes-hall↗

arXiv2026

Breaking conservation law enables steady-state entanglement out of equilibrium

We show how entangled steady states can be prepared by purely dissipative dynamics in a system coupled to a thermal environment. While entanglement is hindered by thermalization when the system and environment exchange a conserved quantity, we demonstrate that breaking this conservation law through the system-environment interaction drives the system to a nonequilibrium steady state. Such an interaction will generate multiple competing equilibration channels, effectively mimicking baths at distinct chemical potentials. When the environment also supports long-range correlations, these channels mediate nonlocal dissipation capable of generating entanglement. We illustrate the scheme in a model of two nitrogen-vacancy (NV) centers weakly coupled to a spin-pumped magnet, where tuneable magnon excitations enable steady-state entanglement over finite distances. Our results identifies a general mechanism for dissipative entanglement generation, rooted in the conservation structure and environmental correlations rather than fine-tuned coherent control or active driving.

quant-ph↗

arXiv2026

Nanoscale observation and control of quasiparticle induced magnetic noise in a superconducting resonator

Superconducting circuits are arguably taking a leading role in driving the ongoing quantum technological revolution. A detailed knowledge of the microscopic fluctuating electromagnetic properties plays an important role in advancing the circuitry design, testing, and material integration of cutting-edge superconducting quantum electronics. Here we report scanning nitrogen-vacancy (NV) quantum sensing of local magnetic noise environment of an on- chip superconducting resonator. We find that quasiparticle-induced fluctuating magnetic fields can drive NV spin relaxation, which shows a peak value around the superconducting transition point of niobium at the thermal equilibrium state. External microwave driving at the resonator mode frequency significantly increases the quasiparticle density, leading to enhancement of magnetic noise. We further perform optically detected magnetic resonance measurements to demonstrate quasiparticle magnetic noise mediated off-resonant dipole coupling between the NV center and niobium resonator. Our work reports experimental observation of the Hebel-Slichter peak signature by an external sensor outside of a superconductor. The presented study also highlights the advantages of quantum sensors in investigating miniaturized superconducting devices, providing insights into their future performance improvements.

cond-mat.mes-hall↗

arXiv2026

Magnon Nesting in Driven Two-Dimensional Quantum Magnets

We uncover a new class of dynamical quantum instability in driven magnets leading to emergent enhancement of antiferromagnetic correlations even for purely ferromagnetic microscopic couplings. A primary parametric amplification creates a frequency-tuned nested magnon distribution in momentum space, which seeds a secondary instability marked by the emergence of enhanced antiferromagnetic correlations, mirroring the instability of nested Fermi surfaces in electronic systems. In sharp contrast to the fermionic case, however, the magnon-driven instability is intrinsically non-equilibrium and fundamentally inaccessible in thermal physics. Its quantum mechanical origin sets it apart from classical instabilities such as Faraday and modulation instabilities, which underlie several instances of dynamical behavior observed in magnetic and cold-atom systems.

cond-mat.mtrl-sci↗

arXiv2025

Proposal for spin superfluid quantum interference device

In easy-plane magnets, the spin superfluid phase was predicted to facilitate coherent spin transport. So far, experimental evidence remains elusive. In this Letter, we propose an indirect way to sense this effect via the spin superfluid quantum interference device (spin SQUID), inspired by its superconducting counterpart (rf SQUID). The spin SQUID is constructed as a quasi-one-dimensional (1D) magnetic ring with a single Josephson weak link, functioning as an isolated device with a microwave response. The spin current is controlled by an in-plane electric field through Dzyaloshinskii-Moriya interaction. This interaction can be interpreted as a gauge field that couples to the spin supercurrent through the Aharonov-Casher effect. By investigating the static and dynamic properties of the device, we show that the spin current and the harmonic frequencies of the spin superfluid are periodic with respect to the accumulated Aharonov-Casher phase and are, therefore, sensitive to the radial electric flux through the ring in units of an electric flux quantum, suggesting a potential electric-field sensing functionality. For readout, we propose to apply spectroscopic analysis to detect the frequency shift of the harmonic modes induced by this magnonic Stark effect.

cond-mat.mes-hall↗

arXiv2025

Topological hydrodynamics in spin-triplet superconductors

Due to the structure of the underlying SO(3) $\mathbf d$-vector order parameter, spin triplet superconductors exhibit a bulk-edge correspondence linking the circulation of supercurrent to the bulk magnetic skyrmion density, giving rise to topological hydrodynamics of magnetic skyrmions. To probe the interplay of charge and spin dynamics, we propose a blueprint for a spin-triplet superconducting quantum interference device (SQUID), which functions without a Josephson weak link. The triplet SQUID undergoes nonsingular $4π$ phase slips, in which current relaxation is facilitated by spin dynamics that trace out a magnetic skyrmion texture. Inductively coupling the device to a tank circuit and probing the nonlinear supercurrent response via Oersted field measurements could provide an experimental signature of ferromagnetic spin-triplet superconductivity.

cond-mat.mes-hall↗

arXiv2025

Entangling color centers via magnon-antimagnon pair creation

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.

cond-mat.mes-hall↗

arXiv2025

Superconductivity-enhanced magnetic field noise

We consider the stray magnetic field noise outside a two-dimensional superconductor. Our considerations are motivated by recent experiments, which observed an enhancement in the magnetic field noise below the superconducting critical temperature based on the relaxation of diamond nitrogen-vacancy centers. Such enhancement is not captured by the standard two-fluid model for the superconducting state, recently proposed to explain such NV relaxometry experiments. Instead, we show that a microscopic BCS theory captures such an enhancement, and we compare with a similar theory and phenomenon, known as the Hebel-Schlicter peak (or coherence peak), observed in the relaxation of nuclear spins in the material. The primary difference is that the NV probes long-wavelength magnetic noise outside the sample, while the nuclear spin probes local hyperfine noise inside the sample. Accordingly, the noise probed by the NV depends on its height and can probe, in pristine samples, the superfluid coherence length. Finally, we discuss potential avenues for NVs to probe unconventional superconductivity via deviations from the above BCS theory.

cond-mat.supr-con↗

arXiv2025

Correlated emission of electron-current waves

Correlated emission of light offer a potential avenue for entanglement generation between atomic spins, with potential application for sensing and quantum memory. In this work, we investigate the conditions for the correlated emission by color centers into an electronic bath of conduction electrons. Unlike emission into bosonic modes, electrons can absorb energy via two-particle processes across a large range of length scales. We find that two length scales are particularly relevant: one set by the Fermi velocity and the frequency of the color centers $v_F/Δ$, and the other set by the Fermi wavelength $λ_F \ll v_F/Δ$. Subradiance requires emitters to be spaced at a distance closer than the Fermi wavelength, while superradiance requires spacing less than $\sqrt{λ_F v_F/Δ}$, so long as the emitters are initialized with coherence. We show that the emitted current burst has a spiral form, and we discuss the experimental possibility to observe correlated dissipation by color-center qubits coupled to electronic environments.

quant-ph↗

arXiv2025

Topological transport of vorticity on curved magnetic membranes

In this work, we study the transport of vorticity on curved dynamical two-dimensional magnetic membranes. We find that topological transport can be controlled by geometrically reducing symmetries, enabling processes absent from flat magnetic systems. To this end, the vorticity 3-current is constructed, which obeys a continuity equation immune to local disturbances of the magnetic texture and spatiotemporal fluctuations of the membrane. We show how electric current can manipulate vortex transport in geometrically nontrivial magnetic systems. As an illustrative example, we propose a minimal setup that realizes an experimentally feasible energy storage device and discuss its thermodynamic efficiency in terms of a vortexoelectric counterpart of the thermoelectric figure of merit $ZT$.

cond-mat.mes-hall↗

arXiv2025

Pseudo-Hermitian physics from dynamically coupled macrospins

We consider two classical macrospins with dynamical (frequency-dependent) coupling, modeled by a generalized Landau-Lifshitz-Gilbert equation. We show that, in the absence of local damping, the resulting dynamics are pseudo-Hermitian. When two precessional modes hybridize near a crossing, the spectral behavior takes the form either of an anticrossing or level attraction, with the latter formalized in terms of spontaneous $\mathcal{PT}$-symmetry breaking. Near equilibrium, mixing due to nondissipative interactions results in repulsion, while dissipative mixing results in attraction. In contrast, when the fluctuating degrees of freedom form a free-energy saddle point, we find that nondissipative interactions result in level attraction, while dissipative interactions produce level repulsion. Accounting for the effects of local Gilbert damping, we examine the cases in which approximate $\mathcal{PT}$-symmetry breaking is still possible and determine the degree to which the qualitative spectral properties still persist.

cond-mat.mes-hall↗

arXiv2024

Proposal for a nonadiabatic geometric gate with an Andreev spin qubit

We study a hybrid structure of a ferromagnetic-insulator and a superconductor connected by a weak link, which accommodates Andreev bound states whose spin degeneracy is lifted due to the exchange interaction with the ferromagnet. The resultant spin-resolved energy levels realize a two-state quantum system, provided that a single electron is trapped in the bound state, i.e., an Andreev spin qubit. The qubit state can be manipulated by controlling the magnetization dynamics of the ferromagnet, which mediates the coupling between external fields and the qubit. In particular, our hybrid structure provides a simple platform to manipulate and control the spin qubit using spintronic techniques. By employing a modified Hahn spin echo protocol for the magnetization dynamics, we show that our Andreev spin qubit can realize a nonadiabatic geometric gate.

cond-mat.mes-hall↗

arXiv2024

Superconducting magnetoelectric effects in mesoscopic hybrid structures

In superconductors that lack inversion symmetry, a supercurrent flow can lead to nondissipative magnetoelectric effects. We offer a straightforward formalism to obtain a supercurrent-induced magnetization in superconductors with broken inversion symmetry, which may have orbital, layer, sublattice, or valley degrees of freedom, multiband noncentrosymmetric superconductors. The nondissipative magnetoelectric effect may find applications in fabricating quantum computation platforms or efficient superconducting spintronic devices. We explore how the current-induced magnetization can be employed to create and manipulate Majorana zero modes in a simple hybrid structure.

cond-mat.mes-hall↗

arXiv2024

Scalar Spin Chirality Hall Effect

The scalar spin chirality, which characterizes the fundamental unit of noncoplanar spin structures, plays an important role in rich chiral physics of magnetic materials. In particular, the intensive research efforts over the past two decades have demonstrated that the scalar spin chirality is the source of various novel Hall transports in solid-state systems, offering a primary route to bring about chiral phenomena in condensed matter physics. However, in all of the previous studies, the scalar spin chirality has been given as a stationary background, serving only a passive role in the transport properties of materials. It remains an open question whether or not the scalar spin chirality itself can exhibit a Hall-type transport. In this work, we show that the answer is yes: The scalar spin chirality is Hall-transported in Kagome ferromagnets and antiferromagnets under an external bias, engendering a phenomenon which we dub the scalar spin chirality Hall effect. Notably, this effect is present even in the absence of any spin-orbit coupling. The analytical theory for the scalar spin chirality Hall effect is corroborated by atomistic spin simulations. Our findings call for the need to lift the conventional assumption that the scalar spin chirality is a passive background in order to discover the active roles of the scalar spin chirality in transport properties.

cond-mat.mes-hall↗

arXiv2024

Flavors of Magnetic Noise in Quantum Materials

The complexity of electronic band structures in quantum materials offers new charge-neutral degrees of freedom stable for transport, a promising example being the valley (axial) degree of freedom in Weyl semimetals (WSMs). A noninvasive probe of their transport properties is possible by exploiting the frequency dependence of the magnetic noise generated in the vicinity of the material. In this work, we investigate the magnetic noise generically associated with diffusive transport using a systematic Langevin approach. Taking a minimal model of magnetic WSMs for demonstration, we show that thermal fluctuations of the charge current, the valley current, and the magnetic order can give rise to magnetic noise with distinctively different spectral characters, which provide a theoretical guidance to separate their contributions. Our approach is extendable to the study of magnetic noise and its spectral features arising from other transport degrees of freedom in quantum materials.

cond-mat.mes-hall↗

arXiv2024

Tracing Dirac points of topological surface states by ferromagnetic resonance

Ferromagnetic resonance is used to reveal features of the buried electronic band structure at interfaces between ferromagnetic metals and topological insulators. By monitoring the evolution of magnetic damping, the application of this method to a hybrid structure consisting of a ferromagnetic layer and a 3D topological insulator reveals a clear fingerprint of the Dirac point and exhibits additional features of the interfacial band structure not otherwise observable. The underlying spin-pumping mechanism is discussed in the framework of dissipation of angular momentum by topological surface states (TSSs). Tuning of the Fermi level within the TSS was verified both by varying the stoichiometry of the topological insulator layer and by electrostatic backgating and the damping values obtained in both cases show a remarkable agreement. The high energy resolution of this method additionally allows us to resolve the energetic shift of the local Dirac points generated by local variations of the electrostatic potential. Calculations based on the chiral tunneling process naturally occurring in TSS agree well with the experimental results.

cond-mat.mes-hall↗

arXiv2024

Magnon kinetic theory of the antiferromagnetic Hanle effect

Motivated by the recently discovered magnonic Hanle effect in an insulating antiferromagnet [Wimmer et al., Phys. Rev. Lett. 125, 247204 (2020)], we develop a spin transport theory based on low-energy waves of antiferromagnetic Néel order. These waves have two polarizations, which we describe in analogy to optics using the Stokes vector on the Poincaré sphere. We find that the polarization, which encodes the magnon spin angular momentum, changes periodically with a frequency that is nonlinear in the magnetic field. This explains the observed asymmetry in the Hanle signal as a function of the magnetic field, along with other salient experimental features. By providing an energy-resolved description of the spin injection, our theory combines the kinetic transport of magnons with the coherent dynamics of their polarization in an intuitive way. This opens a general perspective on a coherent control of magnonic spin density in collinear antiferromagnets.

cond-mat.mes-hall↗

arXiv2024

Cavity magnonics with domain walls in insulating ferromagnetic wires

Magnetic domain walls (DWs) are topological defects that exhibit robust low-energy modes that can be harnessed for classical and neuromorphic computing. However, the quantum nature of these modes has been elusive thus far. Using the language of cavity optomechanics, we show how to exploit a geometric Berry-phase interaction between the localized DWs and the extended magnons in short ferromagnetic insulating wires to efficiently cool the DW to its quantum ground state or to prepare nonclassical states exhibiting a negative Wigner function that can be extracted from the power spectrum of the emitted magnons. Moreover, we demonstrate that magnons can mediate long-range entangling interactions between qubits stored in distant DWs, which could facilitate the implementation of a universal set of quantum gates. Our proposal relies only on the intrinsic degrees of freedom of the ferromagnet, and can be naturally extended to explore the quantum dynamics of DWs in ferrimagnets and antiferromagnets, as well as quantum vortices or skyrmions confined in insulating magnetic nanodisks.

cond-mat.mes-hall↗