arXiv subjects

V. A. S. V. Bittencourt

Publications and source records attributed to V. A. S. V. Bittencourt.

At least 19 recordsLinked to original sources

arXiv2026

Chiral phonons driven by chiral cavities

Lattice vibrations carrying angular momentum give rise to fundamental phenomena such as the phonon Hall effect and the Einstein-de Haas effect, offering new opportunities for manipulating angular momentum in condensed-matter systems. Generating such circularly polarized phonons requires either the use of an external magnetic field, or of polarized light pulses. The latter approach does not require the use of any magnetic response of the material, but it has limitations, in particular regarding the duration of the pulse. Consequently, any effect stemming from phonons generated by light pulses is transient. In this paper, we propose the use of a driven electromagnetic cavity as a route to generate a steady-state population of chiral phonons. We derive a general description of cavity-chiral phonon interaction, with a particular focus on modes of chiral cavities. We show that, under optimized conditions, a significant effective phonon-induced magnetic field can be generated by means of an external drive with realistic power. Our approach is specially tailored for Gamma point phonons with THz frequencies, and opens a new route for investigating chiral phonons with electromagnetic cavities.

cond-mat.mes-hall↗

arXiv2026

Optics-microwave entanglement and state teleportation mediated by a cavity magnomechanical system

Generating usable output-entanglement in continuous variable systems can serve as a viable resource for improving applications in quantum information science. In this work, we show how to generate steady-state output-entanglement in a two-stage conversion setup between optical and microwave photon which employs resonantly coupled magnetic and mechanical excitations, as proposed in Phys. Rev. Applied 18, 044059 (2022). We show that the entanglement can be maximized for the same set of parameters which optimize the frequency-conversion efficiency, and that it can be leveraged for a teleportation-based state-transfer protocol for coherent input-states with fidelity close to unity. We propose an implementation based on an Yittrium Iron Garnet disk of micrometer scale, and use both simulation results and reasonable estimates to assess the performance under optimized conditions. We find a maximum teleportation fidelity of $0.75$ for the proposed setup.

quant-ph↗

arXiv2026

Quantum-impurity sensing of altermagnetic order

Quantum sensing with individual spin defects has emerged as a versatile platform to probe microscopic properties of condensed matter systems. Here we demonstrate that quantum relaxometry with nitrogen-vacancy (NV) centers in diamond can reveal the anisotropic spin dynamics of altermagnetic insulators together with their characteristic spin polarised bands. We show that the distance and orientation dependent relaxation rate of a nearby quantum impurity encodes signatures of momentum space anisotropy in the spin diffusion response, a hallmark of altermagnetic order. This directional sensitivity is unprecedented in the landscape of quantum materials sensing, and it enables the distinction of altermagnets from conventional antiferromagnets via local, noninvasive measurements. Our results could spark new NV-sensing experiments on spin transport and symmetry breaking in altermagnets, and highlight the role of NV orientation to probe anisotropic phenomena in condensed matter systems.

cond-mat.mes-hall↗

arXiv2026

Overcoming intrinsic material limitations through cavity feedback

Magnons, the quanta of spin waves, have significant potential for use in modern technologies, especially when strongly coupled to another mode for read-out and control. However, while magnons strongly interact with microwave photons via the magnetic-dipole interaction to form hybrid cavity-magnon polariton modes, the weak magnetostrictive magnon-phonon interaction, together with large polariton linewidths dominated by magnon dissipation, has so far restricted magnonic-spheres to the weak-coupling regime. The material-limited magnon dissipation rate in particular has been regarded as an unavoidable limitation in these systems. Here, we surpass this long-standing limitation by implementing an active microwave feedback loop to suppress the linewidth of cavity-magnon polaritons and strongly suppress their effective decay rate below the magnon-limited linewidth, thereby enhancing the polariton-phonon cooperativity from C=1 to C=150. As a key milestone, we achieve normal-mode splitting between a cavity-magnon polariton and a mechanical mode, providing direct evidence of three-mode hybridization among photons, magnons, and phonons. Our results establish feedback as a general route to accessing strong-coupling regimes in systems previously thought to be limited by material properties and hence open new opportunities for coherent control in hybrid quantum systems.

cond-mat.mes-hall↗

arXiv2025

Photonic crystal cavities based on suspended yttrium iron garnet nanobeams

We report the fabrication and optical characterization of an air-suspended photonic crystal nanobeam cavity in yttrium-iron-garnet (YIG) realized by focused-ion-beam milling. YIG's combination of low optical loss and ferrimagnetism makes it highly attractive for quantum technologies, yet prior work has largely been focused on millimeter-scale spheres and simple microstructures, hindering true on-chip integration. Demonstrating nanometer-scale patterning in a suspended geometry therefore represents an important advance. Finite-element simulations predict that the same structure supports a flapping-type mechanical mode at $Ω/ 2π\approx 1.52 \,\text{GHz}$ and a backward-volume spin-wave mode at $Ω/ 2π= 11.59 \,\text{GHz}$ under an in-plane bias field. Although we measure only the photonic resonance (intrinsic $Q \sim 2 \times 10^{3}$) in this study, the device lays the groundwork for future exploration of coupled photon-phonon-magnon dynamics once higher optical quality factors are achieved.

physics.app-ph↗

arXiv2025

Generation of Large Amplitude Phonon States in Quantum Acoustics

The development of quantum acoustics has enabled the cooling of mechanical objects to their quantum ground state, generation of mechanical Fock-states, and Schrodinger cat states. Such demonstrations have made mechanical resonators attractive candidates for quantum information processing, metrology, and macroscopic tests of quantum mechanics. However, generating large-amplitude phonon states in quantum acoustic systems has been elusive. In this work, a single superconducting qubit coupled to a high-overtone bulk acoustic resonator is used to generate a large phonon population in an acoustic mode of a high-overtone resonator. We observe extended ringdowns of the qubit, confirming the generation of a large amplitude phonon state, and also observe an upper threshold behavior, a consequence of phonon quenching predicted by our model. This work provides a key tool for generating arbitrary phonon states in circuit quantum acoustodynamics, which is important for fundamental and quantum information applications.

quant-ph↗

arXiv2024

High-Coherence Quantum Acoustics with Planar Superconducting Qubits

Quantum acoustics is an emerging platform for hybrid quantum technologies enabling quantum coherent control of mechanical vibrations. High-overtone bulk acoustic resonators (HBARs) represent an attractive mechanical implementation of quantum acoustics due to their potential for exceptionally high mechanical coherence. Here, we demonstrate an implementation of high-coherence HBAR quantum acoustics integrated with a planar superconducting qubit architecture, demonstrating an acoustically-induced-transparency regime of high cooperativity and weak coupling, analogous to the electrically-induced transparency in atomic physics. Demonstrating high-coherence quantum acoustics with planar superconducting devices enables new applications for acoustic resonators in quantum technologies.

quant-ph↗

arXiv2024

Magnon-microwave backaction noise evasion in cavity magnomechanics

In cavity magnomechanical systems, magnetic excitations couple simultaneously with mechanical vibrations and microwaves, incorporating the tunability of magnetism and the long lifetimes of mechanical modes. Applications of such systems, such as thermometry and sensing, require precise measurement of the mechanical degree-of-freedom. In this paper, we propose a scheme for realizing backaction evading measurements of the mechanical vibrations in cavity magnomechanics. Our proposal involves driving the microwave cavity with two tones separated by twice the phonon frequency and with amplitudes satisfying a balance relation. We show that the minimum added imprecision noise is obtained for drives centered around the lower frequency magnon-microwave polaritons, which can beat the standard quantum limit at modest drive amplitudes. Our scheme is a simple and flexible way of engineering backaction evasion measurements that can be further generalized to other multimode systems.

cond-mat.mes-hall↗

arXiv2023

Magnomechanical backaction corrections due to coupling to higher order Walker modes and Kerr nonlinearities

The radiation pressure-like coupling between magnons and phonons in magnets can modify the phonon frequency (magnomechanical spring effect) and decay rate (magnomechanical decay) via dynamical backaction. Such effects have been recently observed by coupling the uniform magnon mode of a magnetic sphere (the Kittel mode) to a microwave cavity. In particular, the ability to evade backaction effects was demonstrated [C.A. Potts et al., arXiv:2211.13766 [quant-ph] (2022)], a requisite for applications such as magnomechanical based thermometry. However, deviations were observed from the predicted magnomechanical decay rate within the standard theoretical model. In this work, we account for these deviations by considering corrections due to (i) magnetic Kerr nonlinearities and (ii) the coupling of phonons to additional magnon modes. Provided that such additional modes couple weakly to the driven cavity, our model yields a correction proportional to the average Kittel magnon mode occupation. We focus our results on magnetic spheres, where we show that the magnetostatic Walker modes couple to the relevant mechanical modes as efficiently as the Kittel mode. Our model yields excellent agreement with the experimental data.

cond-mat.mes-hall↗

arXiv2022

Optimal broad-band frequency conversion via a magnomechanical transducer

Developing schemes for efficient and broad-band frequency conversion of quantum signals is an ongoing challenge in the field of modern quantum information. Especially the coherent conversion between microwave and optical signals is an important milestone towards long-distance quantum communication. In this work, we propose a two-stage conversion protocol, employing a resonant interaction between magnetic and mechanical excitations as a mediator between microwave and optical photons. Based on estimates for the coupling strengths under optimized conditions for yttrium iron garnet, we predict close to unity conversion efficiency without the requirement of matching cooperativities. We predict a conversion bandwidth in the regions of largest efficiency on the order of magnitude of the coupling strengths which can be further increased at the expense of reduced conversion efficiency.

cond-mat.mes-hall↗

arXiv2022

Complete complementarity relations for quantum correlations in neutrino oscillations

We analyze quantum correlations and quantum coherence in neutrino oscillations. To this end, we exploit complete complementarity relations (CCR) that fully characterize the interplay between different correlations encoded in a quantum system both for pure and mixed states. We consider the CCR for neutrino oscillations both in the case of plane-waves (pure state) and of wave packets (mixed state). In this last case we find a complex structure of correlations depending on the mixing angle, and we show the connection with the non local advantage of quantum coherence, a relevant quantifier of coherence.

quant-ph↗

arXiv2021

Optomagnonics in dispersive media: magnon-photon coupling enhancement at the epsilon-near-zero frequency

Reaching strong light-matter coupling in solid-state systems has been long pursued for the implementation of scalable quantum devices. Here, we put forward the concept of a platform capable of achieving strong coupling between magnetic excitations (magnons) and optics based in an epsilon-near-zero medium, that's it, a medium in which the permittivity is close to zero. We adopt a phenomenological approach to quantize the electromagnetic field inside a dispersive magnetic medium and obtain a Hamiltonian describing the interaction between photons and magnons and the frequency-dependent coupling. We predict that, in the epsilon-near-zero regime, the single-magnon photon optomagnonic coupling can be comparable to the uniform magnon's frequency for small magnetic volumes. For state-of-the-art illustrative values, this would correspond to achieving the single-magnon strong coupling regime, where the coupling rate is larger than all the decay rates. Finally, we show that the non-linear energy spectrum intrinsic to this coupling regime regime can be probed via the characteristic multiple magnon sidebands in the photon power spectrum.

cond-mat.mes-hall↗

arXiv2021

Light propagation and magnon-photon coupling in optically dispersive magnetic media

Achieving strong coupling between light and matter excitations in hybrid systems is a benchmark for the implementation of quantum technologies. We recently proposed [arXiv:2110.02984] that strong single-particle coupling between magnons and light can be realized in a magnetized epsilon-near-zero (ENZ) medium, in which magneto-optical effects are enhanced. Here we present a detailed derivation of the magnon-photon coupling Hamiltonian in dispersive media both for degenerate and non-degenerate optical modes, and show the enhancement of the coupling near the ENZ frequency. Moreover, we show that the coupling of magnons to plane-wave non-degenerate Voigt modes vanishes at specific frequencies due to polarization selection rules tuned by dispersion. Finally, we present specific results using a Lorentz dispersion model. Our results pave the way for the design of dispersive optomagnonic systems, providing a general theoretical framework for describing engineering ENZ-based optomagnonic systems.

cond-mat.mes-hall↗

arXiv2021

Roadmap on Spin-Wave Computing

Magnonics is a field of science that addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operations in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors that covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with Boolean digital data, unconventional approaches like neuromorphic computing, and the progress towards magnon-based quantum computing. The article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or a group of authors and concludes with a brief description of the current challenges and the outlook of the further development of the research directions.

physics.app-ph↗

arXiv2021

Dynamical Backaction Magnomechanics

Dynamical backaction resulting from radiation pressure forces in optomechanical systems has proven to be a versatile tool for manipulating mechanical vibrations. Notably, dynamical backaction has resulted in the cooling of a mechanical resonator to its ground-state, driving phonon lasing, the generation of entangled states, and observation of the optical-spring effect. In certain magnetic materials, mechanical vibrations can interact with magnetic excitations (magnons) via the magnetostrictive interaction, resulting in an analogous magnon-induced dynamical backaction. In this article, we directly observe the impact of magnon-induced dynamical backaction on a spherical magnetic sample's mechanical vibrations. Moreover, dynamical backaction effects play a crucial role in many recent theoretical proposals; thus, our work provides the foundation for future experimental work pursuing many of these theoretical proposals.

cond-mat.mes-hall↗

arXiv2020

Antiferromagnetic cavity optomagnonics

Currently, there is a growing interest in studying the coherent interaction between magnetic systems and electromagnetic radiation in a cavity, prompted partly by possible applications in hybrid quantum systems. We propose a multimode cavity optomagnonic system based on antiferromagnetic insulators, where optical photons couple coherently to the two homogeneous magnon modes of the antiferromagnet. These have frequencies typically in the THz range, a regime so far mostly unexplored in the realm of coherent interactions, and which makes antiferromagnets attractive for quantum transduction from THz to optical frequencies. We derive the theoretical model for the coupled system, and show that it presents unique characteristics. In particular, if the antiferromagnet presents hard-axis magnetic anisotropy, the optomagnonic coupling can be tuned by a magnetic field applied along the easy axis. This allows to bring a selected magnon mode into and out of a dark mode, providing an alternative for a quantum memory protocol. The dynamical features of the driven system present unusual behavior due to optically induced magnon-magnon interactions, including regions of magnon heating for a red detuned driving laser. The multimode character of the system is evident in a substructure of the optomagnonically induced transparency window.

cond-mat.mes-hall↗

arXiv2020

Magnon-Phonon Quantum Correlation Thermometry

A large fraction of quantum science and technology requires low-temperature environments such as those afforded by dilution refrigerators. In these cryogenic environments, accurate thermometry can be difficult to implement, expensive, and often requires calibration to an external reference. Here, we theoretically propose a primary thermometer based on measurement of a hybrid system consisting of phonons coupled via a magnetostrictive interaction to magnons. Thermometry is based on a cross-correlation measurement in which the spectrum of back-action driven motion is used to scale the thermomechanical motion, providing a direct measurement of the phonon temperature independent of experimental parameters. Combined with a simple low-temperature compatible microwave cavity read-out, this primary thermometer is expected to become a popular thermometer for experiments below 1 K.

physics.app-ph↗

arXiv2019

Magnon heralding in cavity optomagnonics

In the emerging field of cavity optomagnonics, photons are coupled coherently to magnons in solid-state systems. These new systems are promising for implementing hybrid quantum technologies. Being able to prepare Fock states in such platforms is an essential step towards the implementation of quantum information schemes. We propose a magnon-heralding protocol to generate a magnon Fock state by detecting an optical cavity photon. Due to the peculiarities of the optomagnonic coupling, the protocol involves two distinct cavity photon modes. Solving the quantum Langevin equations of the coupled system, we show that the temporal scale of the heralding is governed by the magnon-photon cooperativity and derive the requirements for generating high fidelity magnon Fock states. We show that the nonclassical character of the heralded state, which is imprinted in the autocorrelation of an optical "read" mode, is only limited by the magnon lifetime for small enough temperatures. We address the detrimental effects of nonvacuum initial states, showing that high fidelity Fock states can be achieved by actively cooling the system prior to the protocol.

cond-mat.mes-hall↗