arXiv subjects

L. Chotorlishvili

Publications and source records attributed to L. Chotorlishvili.

At least 19 recordsLinked to original sources

arXiv2026

Hopf bifurcation and stochastic spiking in an antiferromagnetic FitzHugh--Nagumo normal form

Antiferromagnets offer ultrafast, stray-field-free dynamics that are attractive for neuromorphic spintronic devices. Here we analyze an antiferromagnetic spin-Hall nano-oscillator in the overdamped regime and derive a reduced set of equations for the Néel-vector dynamics constrained to the unit sphere. For spin polarization along the easy axis, the model reduces to an asymmetric rotator, for which analytic solutions and the associated spin-pumping signal are obtained in selected limits. We further show that near a suitable operating point, the projected dynamics can be transformed into a local FitzHugh-Nagumo normal form. The resulting mapping identifies the effective fast variable, recovery variable, bias current, and Hopf condition in terms of magnetic material parameters. We finally extend the reduced model to an Itô stochastic FitzHugh-Nagumo equation driven by spin-pumping input and additive thermal or electronic fluctuations. The stochastic phase portrait shows that the deterministic nullcline geometry organizes noisy spike cycles and produces controlled spike-time variability. These results provide a minimal analytic framework for AFM-based spiking-neuron elements and suggest design criteria for future neuromorphic spintronic devices.

nlin.CD↗

arXiv2026

Entanglement between quantum dots transmitted via Majorana wire: Insights from the fermionic negativity, concurrence and quantum mutual information

We study quantum entanglement in a system comprising two quantum dots interconnected through the short topological superconducting nanowire, which hosts overlapping boundary Majorana modes. Inspecting the fermionic negativity, we analyze the variation of entanglement against the position of the energy levels of quantum dots and their hybridization with the topological superconducting nanowire. In the absence of electron correlations, the optimal entanglement occurs when the energy levels coincide with the zero-energy Majorana modes, whereas upon increasing the hybridizations, the entanglement is gradually suppressed. Such monotonous behavior is no longer valid when the quantum dot levels are detuned from the zero-energy. Under these circumstances, the quantum dots become maximally entangled for a certain optimal hybridization. Moreover, we study the thermal concurrence to explore the entanglement properties at finite temperatures. We also compute the quantum mutual information and propose recipes for robust finite-temperature entanglement transmission via Majorana modes.

quant-ph↗

arXiv2025

Quantum Skyrmion Qudit in a Triangular-lattice magnet

Since the pioneering work Lohani et. al., Phys. Rev. X 9, 041063 (2019), it became clear that quantum skyrmions have highly unusual properties as compared to the classical skyrmions and, due to their quantumness, cannot be described by continuous magnetic textures akin to the classical skyrmions. Competing nearest-neighbor and next-nearest-neighbor ferromagnetic and antiferromagnetic interactions in triangular spin-frustrated magnets lead to the formation of quantum skyrmion states. In frustrated magnets, skyrmions are characterized by the helical degree of freedom, which can store quantum information. In the limit of a weak electric field, the system can be described as a two-level system, i.e., a skyrmion qubit. Here, we propose a more general formulation of the problem and obtain general analytic solution of the model previously introduced in Psaroudaki et. al., Phys. Rev. Lett. 127, 067201 (2021). Our solution is valid not only for small barrier but for the arbitrary electric field. In the case of a significant barrier, we prove that the system's state is not a Skyrmion qubit as it was thought before, but a Skyrmion qudit. We constructed the density matrix of the Skyrmion qudit and studied its evolution in time. The obtained results suggest that the proposed model can be exploited further to meet the needs of quantum information theory and quantum skyrmionics. We showed that the $l_1$ norm of coherence of the skyrmion quantum qudit is a thousand times larger than the coherence of the skyrmion quantum qubit. The obtained result opens new perspectives for quantum skyrmion-based resource theory.

cond-mat.mes-hall↗

arXiv2025

Relativistic quantum entanglement in a bipartite charged scalar system

Continuous variable entanglement in a system of two interacting charged scalar mesons is studied. The mesons mutual interaction is mediated by a central symmetric Coulomb potential. We work out the difference between relativistic and non-relativistic limits on the basis of the continuous variable separability criteria and prove rigorously the following theorem for our system: While a bipartite charged scalar mesonic quantum system with centrally symmetric interaction is entangled in the relativistic regime, its non-relativistic counterpart can be separable with non entanglement.

quant-ph↗

arXiv2025

Entanglement properties of photon-magnon crystal from nonlinear perspective

Quantifying the entanglement between two continuous bosonic modes, such as magnons and photons, is not trivial. The logarithmic negativity, calculated through the quantum Langevin equations is subjected to thermal noise. However this method requires further approximation. The phase space of a generic nonlinear system contains topologically different regions, and the steady state may correspond to the different types of fixed points, such as Saddle Points, Stable or unstable Spirals, and Nodes. In the present work, we propose a new procedure. Namely, we derived the complete set of nonlinear equations, which includes equations for the magnon and photon number operators and phases. We show that not only number operators but also phases are important for exploring the character of the fixed point, and magnon-photon entanglement. We showed that methods of the qualitative theory of nonlinear differential equations are also relevant for photon-magnon entanglement problems. Our main finding is that entanglement is not defined in the Saddle Point region. On the other hand, the maximum of the entanglement corresponds to the region near the border between the Stable node and Stable spiral regions. Our approach is quite general. However, we did calculations for a particular system: photon-magnon crystal based on the yttrium iron garnet (YIG) film with the periodic air holes drilled in the film. Our interest focuses on magnons with a particular wavelength and frequency corresponding to the magnon condensate. Those magnons couple strongly with the photons of similar frequency. We discuss in detail the interaction between magnons and photons originating from the magneto-electric coupling and the effective Dzyaloshinskii-Moriya interaction. We show that this interaction is responsible for the robust photon-magnon entanglement in the system.

cond-mat.mes-hall↗

arXiv2025

Majorana Signatures in the Tripartite Uncertainty Relations with Quantum Memory

Quantumness imposes a fundamental limit on measurement accuracy. The paradigmatic cases are Heisenberg's uncertainty relation in the original formulation, Robertson's formulation, and improved uncertainty relations. However, the more universal measures are given in terms of quantum entropies. Uncertainties of measurements done on one quantum system correlated with another quantum system constitute a more intriguing question. Quantum correlations can influence the lower bound of uncertainties, and the reason for this is the quantum memory. In this article, we study uncertainties of measurements performed on one quantum dot correlated with the second one through the superconductor, hosting the Majorana boundary modes. We prove that the Majorana quasiparticles allow the uncertainties to reach the minimal possible lower bound. By rigorous theoretical considerations, we obtain the result of experimental relevance expressed in terms of only two parameters: the overlap between Majorana modes and their coupling strength with the quantum dots. We show that the overlap between Majorana modes reduces quantum uncertainties, which is a general result of fundamental importance. We also propose the protocol to measure spins in both quantum dots, consecutively, and demonstrate that the result of the second measurement would depend on the presence of Majorana quasiparticles. This could serve as an indirect tool for their empirical observation, which is of importance for the ongoing discussions concerning unambiguous detection of the Majorana quasiparticles in nanoscopic hybrid structures.

quant-ph↗

arXiv2024

Two-level atom witness of thermalization of multimode optical fibers

In the present project, we study the dynamics of the two-level system coupled with the multimode optical system. In particular, we considered a square lattice of optical fibers. We aimed to answer whether we can infer information about the thermalization of optical modes through the thermalization of two-level atoms. After averaging over the set of modes, the dynamic of the two-level system is free of quantum revivals, and that is the signature of thermalization. We showed that the temperature of the two-level system increases with the temperature of optical modes and mean photon number. In the high-temperature limit of optical modes, the temperature of the level system tends to be infinity, and level populations are equal.

physics.optics↗

arXiv2024

The controlled rotation of entanglement in altermagnets

Altermagnetism became very popular because of unique features, namely coupling between magnetic properties and momentum of itinerant electrons. The particular model of the altermagnetic system of our interest has already been studied in recent publications in a different context: Phys. Rev. B \textbf{108}, L140408 (2023). Here, we study the scattering process of an itinerant electron from the altermagnetic system on the electron localized in a quantum dot. We found a spatially inhomogeneous distribution of quantum entanglement in the post-scattering state. An interesting observation is the controlled rotation of entanglement achieved by means of spin-orbital coupling constant in altermagnetic. We also studied Reny entropy and the effect of disorder in the system leading to randomness in the spin-orbit constant. Our main finding is that due to the unique properties of an altermagnetic system, tuning the applied external magnetic field allows tailoring of the desired entangled state. Thus, the scattering process, in essence, mimics the Hadamard-CNOT Gate transformation, converting the initial disentangled state into the entangled state of Bell's state. In particular, we achieved more than 70 percent fidelity between the post-scattering and Bell's states.

cond-mat.stat-mech↗

arXiv2023

Plasmonic skyrmion quantum thermodynamics

The primary obstacle in the field of quantum thermodynamics revolves around the development and practical implementation of quantum heat engines operating at the nanoscale. One of the key challenges associated with quantum working bodies is the occurrence of "quantum friction," which refers to irreversible wasted work resulting from quantum inter-level transitions. Consequently, the construction of a reversible quantum cycle necessitates the utilization of adiabatic shortcuts. However, the experimental realization of such shortcuts for realistic quantum substances is exceedingly complex and often unattainable. In this study, we propose a quantum heat engine that capitalizes on the plasmonic skyrmion lattice. Through rigorous analysis, we demonstrate that the quantum skyrmion substance, owing to its topological protection, exhibits zero irreversible work. Consequently, our engine operates without the need for adiabatic shortcuts. We checked by numerical calculations and observed that when the system is in the quantum skyrmion phase, the propagated states differ from the initial states only by the geometricl and dynamical phases. The adiabacit evoluation leads to the zero transition matrix elements and zero irreversible work. By employing plasmonic mods and an electric field, we drive the quantum cycle. The fundamental building blocks for constructing the quantum working body are individual skyrmions within the plasmonic lattice. As a result, one can precisely control the output power of the engine and the thermodynamic work accomplished by manipulating the number of quantum skyrmions present.

quant-ph↗

arXiv2023

Topological entanglement entropy to identify topological order in quantum skyrmions

We study the topological entanglement entropy and scalar chirality of a topologically ordered skyrmion formed in a two-dimensional triangular lattice. Scalar chirality remains a smooth function of the magnetic field in both helical and quantum skyrmion phases. In contrast, topological entanglement entropy remains almost constant in the quantum skyrmion phase, whereas it experiences enhanced fluctuations in the helical phase. Therefore, topological entanglement entropy is an effective tool to distinguish between the two phases and pinpoint the quantum phase transition in the system.

cond-mat.str-el↗

arXiv2023

Topological insulator and quantum memory

Measurements done on the quantum systems are too specific. Contrary to their classical counterparts, quantum measurements can be invasive and destroy the state of interest. Besides, quantumness limits the accuracy of measurements done on quantum systems. Uncertainty relations define the universal accuracy limit of the quantum measurements. Relatively recently, it was discovered that quantum correlations and quantum memory might reduce the uncertainty of quantum measurements. In the present work, we study two different types of measurements done on the topological system. Namely, we discuss measurements done on the spin operators and the canonical pair of operators: momentum and coordinate. We quantify the spin operator's measurements through the entropic measures of uncertainty and exploit the concept of quantum memory. While for the momentum and coordinate operators, we exploit the improved uncertainty relations. We discovered that quantum memory reduces the uncertainties of spin measurements. On the hand, we proved that the uncertainties in the measurements of the coordinate and momentum operators depend on the value of the momentum and are substantially enhanced at small distances between itinerant and localized electrons (the large momentum limit). We note that the topological nature of the system leads to the spin-momentum locking. The momentum of the electron depends on the spin and vice versa. Therefore, we suggest the indirect measurement scheme for the momentum and coordinate operators through the spin operator. Due to the factor of quantum memory, such indirect measurements in topological insulators have smaller uncertainties rather than direct measurements.

quant-ph↗

arXiv2023

Magnetoelectric fractals, Magnetoelectric parametric resonance and Hopf bifurcation

In the present work, we study the dynamics of a magnetic nanoparticle coupled through the magnetoelectric coupling to the ferroelectric crystal. The model of our interest is nonlinear, and we explore the problem under different limits of weak and strong linearity. By applying two electric fields with different frequencies, we control the form of the confinement potential of the ferroelectric subsystem and realize different types of dynamics. We proved that the system is more sensitive to magnetoelectric coupling in the case of double-well potential. In particular, in the case of strong nonlinearity, arbitrary small values of magnetoelectric coupling lead to chaotic dynamics. In essence, magnetoelectric coupling plays a role akin to the small perturbations destroying invariant tors according to the KAM theorem. We showed that bifurcations in the system are of Hopf's type. We observed the formation of magnetoelectric fractals in the system. In the limit of weak nonlinearity, we studied a problem of parametric nonlinear resonance and enhancement of magnetic oscillations through magnetoelectric coupling.

cond-mat.mes-hall↗

arXiv2023

Superconducting Diode sensor

We study the superconducting Josephson junction diode operating via the magnetic field of skyrmions. Inspired by the near-field optical microscopy, we propose to partially screen the magnetic field and analyze part-by-part the magnetic texture of the skyrmion. The detected asymmetric supercurrent is influenced by the skyrmionic magnetic field and magnetic texture. This enables the Josephson junction diode to function as a hyperfine sensor and to read out the information about the morphology of the complex magnetic textures. The proposed setup opens a new avenue in magnetometry and represents an alternative to the technologies based on the nitrogen-vacancy centers.

cond-mat.supr-con↗

arXiv2023

Topological dynamical quantum phase transition in a quantum skyrmion phase

Quantum skyrmionic phase is modelled in a 2D helical spin lattice. This topological skyrmionic phase retains its nature in a large parameter space before moving to a ferromagnetic phase. Next nearest-neighbour interaction improves the stability and it also causes a shift of the topological phase in the parameter space. Nonanalytic behaviour of the rate function observed, when the system which is initially in a quantum skyrmion phase is quenched to a trivial quantum ferromagnetic phase, indicates a dynamical quantum phase transition. Dynamical quantum phase transition is absent when the system initially in a skyrmion phase is quenched to a helical phase.

cond-mat.str-el↗

arXiv2023

Steering skyrmions with microwave and THz electric pulses

Tools for controlling electrically the motion of magnetic skyrmions are important elements towards their use in spintronic devices. Here, we propose and demonstrate the transport of skyrmions via GHz and THz electric pulses. The method relies on using polarization textured pulses such that the skyrmion experiences (via its inherent magnetoelectricity) the out-of-plane and in-plane components of the pulse electric field. It is shown how the electric field drags efficiently the skyrmion. The control of the skyrmion motion depends solely on the amplitude of electric fields, frequency, polarization, or phase in case two pulses are applied. Micromagnetic calculations supported by analytic modeling and analysis indicate the experimental feasibility of the control scheme.

cond-mat.str-el↗

arXiv2022

Random spin-orbit gates in the system of a Topological insulator and a Quantum dot

The spin-dependent scattering process in a system of topological insulator and quantum dot is studied. The unitary scattering process is viewed as a gate transformation applied to an initial state of two electrons. Due to the randomness imposed through the impurities and alloying-induced effects of band parameters, the formalism of the random unitary gates is implemented. For quantifying entanglement in the system, we explored concurrence and ensemble-averaged Rényi entropy. We found that applied external magnetic field leads to long-range entanglement on the distances much larger than the confinement length. We showed that topological features of itinerant electrons sustain the formation of robust long-distance entanglement, which survives even in the presence of a strong disorder.

cond-mat.mes-hall↗

arXiv2022

Skyrmion lattice hosted in synthetic antiferromagnets and helix modes

Thin ferromagnetic films can possess unconventional magnetic properties, opening a new road for using them in spintronic technologies. In the present work exploiting three different methods, we comprehensively analyze phason excitations of a skyrmion lattice in synthetic antiferromagnets. To analyze phason excitations of the skyrmion lattice, we have constructed an analytical model based on three coupled helices and found a linear gapless mode. Micromagnetic simulations also support this result. Moreover, a similar result has been achieved within the rigid skyrmion lattice model based on the coupled Thiele's equations, when the coupling between skyrmions in different layers of the synthetic antiferromagnetic is comparable to or larger than the intralayer coupling. In addition, we also consider the orbital angular momentum and spin pumping current associated with phason excitations. Due to the gapless excitations in the case of skyrmion lattice, the pumping current is nonzero for the arbitrary frequency of pumping microwaves. In the case of individual skyrmions, no current is pumped when microwave frequency is inside the gap of the spectrum of individual skyrmions.

cond-mat.str-el↗

arXiv2022

Skyrmion Echo in a system of interacting Skyrmions

We consider helical rotation of skyrmions confined in the potentials formed by nano-disks. Based on numerical and analytical calculations we propose the skyrmion echo phenomenon. The physical mechanism of the skyrmion echo formation is also proposed. Due to the distortion of the lattice, impurities, or pinning effect, confined skyrmions experience slightly different local fields, which leads to dephasing of the initial signal. The interaction between skyrmions also can contribute to the dephasing process. However, switching the magnetization direction in the nanodiscs (e.g. by spin transfer torque) also switches the helical rotation of the skyrmions from clockwise to anticlockwise (or vice-versa), and this restores the initial signal (which is the essence of skyrmion echo).

cond-mat.str-el↗