arXiv subjects

Jayakrishnan M. P. Nair

Publications and source records attributed to Jayakrishnan M. P. Nair.

17 recordsLinked to original sources

arXiv2026

Quantum magnonics with engineered dissipative and coherent interactions

Cavity magnonics is moving beyond the conventional paradigm of coherent spin--photon hybridization toward the controlled engineering of dissipative and coherent interactions, Floquet dynamics, and quantum fluctuations. This Perspective examines how these ingredients reshape collective dynamics and open new avenues for quantum state engineering, transport, and sensing. We discuss the role of dissipative coupling and anti-$\mathcal{PT}$ symmetry in enabling long-lived collective modes and enhanced spectral response, and highlight Floquet engineering as a means of engineering nonreciprocal transport and phase-controlled interactions. We then review recent progress in quantum magnonics, ranging from squeezed and entangled magnon states, including the squeezing of thermal magnons, to prospective schemes for preparing magnonic Schrödinger-cat states. We also discuss how parametric driving and active gain strongly modify hybrid susceptibilities and amplify magnon--photon response. These advances expand the scope of cavity magnonics beyond conventional polariton physics, establishing it as a versatile platform for sensing, transduction, spin transport, and hybrid quantum technologies.

quant-ph↗

arXiv2026

Asymmetric Floquet-Engineered Mode Coupling in Hybrid Magnonics

In hybrid magnonic systems, linear magnon--photon hybridization inherently produces symmetric, reciprocal interactions, precluding asymmetric mode coupling. Floquet driving can tailor mode coupling strengths but, with single-tone modulation, inevitably generates a symmetric interaction that preserves this reciprocity. Here we introduce dual-tone Floquet modulation to unlock a new degree of freedom in hybrid magnonic systems, where the relative phase $θ$ of two commensurate drives continuously controls the asymmetry of the Floquet-engineered interaction, enabling asymmetric mode coupling absent in existing hybrid magnonic systems. We demonstrate this in a strongly coupled cavity magnonic device, where tuning $θ$ reversibly switches single-sided Autler--Townes splitting between the two hybrid modes---a direct spectroscopic signature of phase-programmable asymmetric coupling. This approach opens a new path toward controllable nonreciprocal and topological functionalities in hybrid magnonic systems, with broad implications for advanced quantum and classical signal processing.

cond-mat.mes-hall↗

arXiv2026

Experimental Realization of Synthetic Magnonic Lattice via Floquet Engineering

Magnonic systems, which exploit spin-wave excitations in magnetic materials, offer a promising platform for coherent information processing due to their low dissipation, strong nonlinearities, and intrinsic nonreciprocity. However, scaling magnonic circuits remains challenging, particularly with low-loss insulators such as yttrium iron garnet (YIG), which are difficult to pattern. Here, we experimentally realize a synthetic dimension in a magnonic system by coupling multimode magnon resonances in the frequency domain using time-periodic Floquet modulation. This approach enables electronically tunable interactions between discrete modes within a single YIG device, forming a reconfigurable mode-space lattice that supports functionalities such as Bloch oscillation. Our results demonstrate that high-dimensional magnonic dynamics can be achieved without increasing device footprint, establishing synthetic dimensions as a scalable and programmable route for integrated magnonic technologies. This advancement positions magnonic systems as promising platforms for engineering emergent phenomena that are inaccessible at equilibrium.

cond-mat.mes-hall↗

arXiv2026

Observation and Control of Spontaneous Magnon Emission from Spin Ensembles in 2D Hexagonal Boron Nitride

Hybrid systems consisting of color centers and magnetic materials provide an appealing solid-state platform for advancing the burgeoning quantum technological revolution. Exploring novel coupling mechanisms between optically active spin defects and quantum degrees of freedom is directly relevant in this context. Here, we report observation and control of spontaneous magnon emission from boron-vacancy centers in 2D hexagonal boron nitride (hBN), an unconventional qubit-magnon dipole coupling channel that dominates in the near-zero temperature limit. The spontaneous magnon emission process starts to be overshadowed by thermal magnon effect as temperature increases, reflecting the crossover from an emission-dominated, effectively cold magnon reservoir to a thermally occupied spin bath where absorption and stimulated processes restore balance. By increasing the spin defect density, we further present that spontaneous magnon emission into a common spin bath could help establish quantum correlations in dense hBN spin ensembles. Our results are quantitatively captured by detailed theoretical modeling, bringing insights into understanding qubit-magnon coupling, correlated spin dynamics, and many-body physics of color centers in the quantum regime.

cond-mat.mes-hall↗

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↗

arXiv2025

Engineering long-lived entanglement through dissipation in quantum hybrid solid-state platforms

Spin squeezing, a form of many-body entanglement, is a crucial resource in quantum metrology and information processing. While experimentally viable protocols for generating stable spin squeezing have been proposed in quantum optics setups, there is growing interest in quantum hybrid solid-state systems as alternative platforms for both engineering and exploring many-body quantum phenomena. In this work, we propose a scheme to generate long-lived spin squeezing in an ensemble of solid-state qubits interacting with electromagnetic noise emitted by a squeezed solid-state bath. We identify the conditions under which quantum correlations within the bath can be transferred to the qubit array, driving it into an entangled state independently of its initial configuration. To assess the experimental feasibility of our approach, we analyze the dynamics of an array of solid-state spin defects coupled to a common ferromagnetic bath, which is driven into a non-equilibrium squeezed state through its interaction with a surface acoustic wave mode. Our results demonstrate that the ensemble can exhibit steady-state spin squeezing under suitable conditions, opening new pathways for the generation of robust many-body entanglement in solid-state spin ensembles.

quant-ph↗

arXiv2024

The role of excitation vector fields and all-polarisation state control of cavity magnonics

Recently the field of cavity magnonics, a field focused on controlling the interaction between magnons and confined microwave photons within microwave resonators, has drawn significant attention as it offers a platform for enabling advancements in quantum- and spin-based technologies. Here, we introduce excitation vector fields, whose polarisation and profile can be easily tuned in a two-port cavity setup, thus acting as an effective experimental knob to explore the coupled dynamics of cavity magnon-polaritons. Moreover, we develop theoretical models that accurately predict and reproduce the experimental results for any polarisation state and field profile within the cavity resonator. This versatile experimental platform offers a new avenue for controlling spin-photon interactions and as such also delivering a mechanism to readily control the exchange of information between hybrid systems.

quant-ph↗

arXiv2024

Magnon-Photon Coupling in an Opto-Electro-Magnonic Oscillator

The opto-electronic oscillators (OEOs) hosting self-sustained oscillations by a time delayed mechanism are of particular interest in long-haul signal transmission and processing. On the other hand, owing to their unique tunability and compatibility, magnons - as elementary excitations of spin waves - are advantageous carriers for coherent signal transduction across different platforms. In this work, we integrated an opto-electronic oscillator with a magnonic oscillator consisting of a microwave waveguide and a yttrium iron garnet sphere. We find that, in the presence of the magnetic sphere, the oscillator power spectrum exhibits sidebands flanking the fundamental OEO modes. The measured waveguide transmission reveals anti-crossing gaps, a hallmark of the coupling between the opto-electronic oscillator modes and the Walker modes of the sphere. Experimental results are well reproduced by a coupled-mode theory that accounts for nonlinear magnetostrictive interactions mediated by the magnetic sphere. Leveraging the advanced fiber-optic technologies in opto-electronics, this work lays out a new, hybrid platform for investigating long distance coupling and nonlinearity in coherent magnonic phenomena.

physics.optics↗

arXiv2023

Topological transitions in dissipatively coupled Su-Schrieffer-Heeger models

Non-Hermitian topological phenomena have gained much interest among physicists in recent years. In this paper, we expound on the physics of dissipatively coupled Su-Schrieffer-Heeger (SSH) lattices, specifically in systems with bosonic and electrical constituents. In the context of electrical circuits, we demonstrate that a series of resistively coupled LCR circuits mimics the topology of a dissipatively coupled SSH model. In addition, we foreground a scheme to construct dissipatively coupled SSH lattices involving a set of non-interacting bosonic oscillators weakly coupled to engineered reservoirs of modes possessing substantially small lifetimes when compared to other system timescales. Further, by activating the coherent coupling between bosonic oscillators, we elucidate the emergence of non-reciprocal dissipative coupling which can be controlled by the phase of the coherent interaction strength precipitating in phase-dependent topological transitions and skin effect. Our analyses are generic, apropos of a large class of systems involving, for instance, optical and microwave settings, while the circuit implementation represents the most straightforward of them.

quant-ph↗

arXiv2023

Engineering bound states in continuum via nonlinearity induced extra dimension

Bound states in continuum (BICs) are localized states of a system possessing significantly large life times with applications across various branches of science. In this work, we propose an expedient protocol to engineer BICs which involves the use of Kerr nonlinearities in the system. The generation of BICs is a direct artifact of the nonlinearity and the associated expansion in the dimensionality of the system. In particular, we consider single and two mode anharmonic systems and provide a number of solutions apposite for the creation of BICs. In close vicinity to the BIC, the steady state response of the system is immensely sensitive to perturbations in natural frequencies of the system and we illustrate its propitious sensing potential in the context of experimentally realizable setups for both optical and magnetic nonlinearities.

quant-ph↗

arXiv2022

Nonlinear construction of topological SSH models

The Su-Schrieffer-Heeger (SSH) model describes a paradigmatic one-dimensional (1-D) system that exhibits a non-trivial band topology. In this paper, we foreground a new scheme involving a 1-D chain of $2N+1$ Bosonic modes with nearest-neighbor interactions, in which, the topology of the system is regulated by the selective excitation of intrinsic anharmonicities. In the dispersive regime, where the characteristic detunings are considerably larger than the coupling strengths, the linearized system is topologically identical to an SSH model. This is marked by the emergence of zero-energy eigenmodes of the system, and we specifically illustrate its rich topology in a chain of size $N=6$. We consider an experimentally realizable lattice involving optical cavities which are coupled to collective systems characterized by Bosonic modes. By investigating the transmission due to a weak probe field, we provide a spectroscopic analysis of the system, demonstrating, for instance, the emergence of bistability at higher pumping rates.

quant-ph↗

arXiv2022

Quantum amplification of spin currents in cavity magnonics by a parametric drive induced long-lived mode

Cavity-mediated magnon-magnon coupling can lead to a transfer of spin-wave excitations between two spatially separated magnetic samples. We enunciate how the application of a two-photon parametric drive to the cavity can lead to stark amplification in this transfer efficiency. The recurrent multiphoton absorption by the cavity opens up an infinite ladder of accessible energy levels, which can induce higher-order transitions within the magnon Fock space. This is reflected in a heightened spin-current response from one of the magnetic samples when the neighboring sample is coherently pumped. The enhancement induced by the parametric drive can be considerably high within the stable dynamical region. Specifically, near the periphery of the stability boundary, the spin current is amplified by several orders of magnitude. Such striking enhancement factors are attributed to the emergence of parametrically induced strong coherences precipitated by a long-lived mode. While contextualized in magnonics, the generality of the principle would allow applications to energy transfer between systems contained in parametric cavities.

quant-ph↗

arXiv2022

Cavity mediated level attraction and repulsion between magnons

We characterize some of the distinctive hallmarks of magnon-magnon interaction mediated by the intracavity field of a microwave cavity, along with their testable ramifications. In general, we foreground two widely dissimilar parameter domains that bring forth the contrasting possibilities of level splitting and level crossing. The former is observed in the regime of strong magnon-photon couplings, particularly when the three modes bear comparable relaxation rates. This character is marked by the appearance of three distinguishable and non-converging polariton branches in the spectral response to a cavity drive. However, when the bare modes are resonant and the couplings perfectly symmetrical, one of the spectral peaks gets wiped out. This anomalous extinction of polaritonic response can be traced down to the existence of a conspicuous dark mode alongside two frequency-shifted bright modes. In an alternate parameter regime, where the magnon modes are weakly coupled to the cavity, features of level attraction unfold, subject to a large relaxation rate for the cavity mode. Concurrently, for antisymmetric detunings to the magnon modes, a transmission window springs into existence, exhibiting transparency in the limit of negligible dissipation from the magnons. The emergence of level attraction can be reconciled with a theoretical model that embodies the dynamics of the magnon-magnon subsystem when the cavity field decays rapidly into its steady state. In this limit, we identify a purely dissipative coupling between the magnon modes.

quant-ph↗

arXiv2021

Anti-PT-symmetry-enhanced interconversion between microwave and optical fields

The intrinsic dissipation of systems into a shared reservoir introduces coherence between two systems, enabling anti-Parity-Time (anti-PT) symmetry. In this paper, we propose an anti-PT symmetric converter, consisting of a microwave cavity coupled dissipatively to a ferromagnetic sphere, which supports significant improvements in the conversion efficiency when compared to coherently coupled setups. In particular, when only the ferrite sample is driven, the strong coherence induced by the vacuum of the mediating channel leads to much stronger enhancements in the intended conversion. The enhancement is an inalienable artifact of the emergence of a long-lived, dark mode associated with a quasi-real singularity of the hybrid system. In addition, we observe considerable asymmetry in the efficiencies of microwave-to-optical and optical-to-microwave conversions, in spite of the symmetrical structure of the trilinear optomagnonic coupling stimulating both the transduction phenomena. The nonreciprocity stems from the intrinsic asymmetry in the couplings of the microwave and optical fields to the cavity-magnon network as well as the phase coupling entailed by the spatial separation.

physics.optics↗

arXiv2021

Ultralow threshold bistability and generation of long-lived mode in a dissipatively coupled nonlinear system: application to magnonics

The prospect of a system possessing two or more stable states for a given excitation condition is of topical interest with applications in information processing networks. In this work, we establish the remote transfer of bistability from a nonlinear resource in a dissipatively coupled two-mode system. As a clear advantage over coherently coupled settings, the dissipative nature of interaction is found to support a lower pumping threshold for bistable signals. For comparable parameters, the bistability threshold for dissipatively coupled systems is lower by a factor of about five. The resulting hysteresis can be studied spectroscopically by applying a probe field through the waveguide and examining the polariton character of the transmitted field. Our model is generic, apropos of an extensive set of quantum systems, and we demonstrate our results in the context of magnonics where experimental interest has flourished of late. As a consequence of dissipative coupling and the nonlinearity, a long-lived mode emerges, which is responsible for heightened transmission levels and pronounced sensitivity in signal propagation through the fiber.

quant-ph↗

arXiv2020

Enhanced sensing of weak anharmonicities through coherences in dissipatively coupled anti-PT symmetric systems

In the last few years, the great utility of PT-symmetric systems in sensing small perturbations has been recognized. Here, we propose an alternate method relevant to dissipative systems, especially those coupled to the vacuum of the electromagnetic fields. In such systems, which typically show anti-PT symmetry and do not require the incorporation of gain, vacuum induces coherence between two modes. Owing to this coherence, the linear response acquires a pole on the real axis. We demonstrate how this coherence can be exploited for the enhanced sensing of very weak anhamonicities at low pumping rates. Higher drive powers ($\sim 0.1$ W), on the other hand, generate new domains of coherences. Our results are applicable to a wide class of systems, and we specifically illustrate the remarkable sensing capabilities in the context of a weakly anharmonic Yttrium Iron Garnet (YIG) sphere interacting with a cavity via a tapered fiber waveguide. A small change in the anharmonicity leads to a substantial change in the induced spin current.

quant-ph↗

arXiv2020

Nonlinear Spin Currents

The cavity mediated spin current between two ferrite samples has been reported by Bai et. al. [Phys. Rev. Lett. 118, 217201 (2017)]. This experiment was done in the linear regime of the interaction in the presence of external drive. In the current paper we develop a theory for the spin current in the nonlinear domain where the external drive is strong so that one needs to include the Kerr nonlinearity of the ferrite materials. In this manner the nonlinear polaritons are created and one can reach both bistable and multistable behavior of the spin current. The system is driven into a far from equilibrium steady state which is determined by the details of driving field and various interactions. We present a variety of steady state results for the spin current. A spectroscopic detection of the nonlinear spin current is developed, revealing the key properties of the nonlinear polaritons. The transmission of a weak probe is used to obtain quantitative information on the multistable behavior of the spin current. The results and methods that we present are quite generic and can be used in many other contexts where cavities are used to transfer information from one system to another, e.g., two different molecular systems.

quant-ph↗