Resonant Exchange Research Articles

Synthesis of flake shaped carbonyl iron/reduced graphene oxide/polyvinyl pyrrolidone ternary nanocomposites and their microwave absorbing properties

Ternary composites of flake shaped carbonyl iron/reduced graphene oxide/polyvinyl pyrrolidone (CI/rGO/PVP) were synthesized via the assembly of positively charged CI and negatively charged graphene oxide (GO) with subsequent chemical reduction and PVP nanoparticles decoration. The preparation of such ternary composites was confirmed by various characterization methods including ξ-potential, scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectrometer (EDS), RAMAN scattering spectroscopy, and X-ray diffraction (XRD). The influence of PVP concentration on the morphology and microwave absorbing property of CI/rGO/PVP composites was studied systematically. The hysteresis loops of pristine flake shaped CI, binary intermediate products and ternary final composites were measured by vibrating sample magnetometer (VSM) to illustrate their statics magnetism characteristics. The microwave absorbing properties of nanocomposites were calculated based on the analysis of electromagnetic parameters measured by vector network analyzer (VNA). According to the relative complex permittivity and relative permeability, dielectric loss of the ternary composites is mainly attributed to the orientational and interfacial polarization, while magnetic loss is prominently ascribed to eddy current loss, natural resonance, exchange resonance and hysteresis loss. The reflection loss (RL) calculation based on transmission line theories demonstrates that as-synthesized composites possess excellent microwave absorbing properties and the product with moderate PVP concentration shows an ultra-wide low reflection (RL < −10 dB) band from 4.2 to 18 GHz with a coating thickness of 2.5 mm. The synergetic effect between dielectric and magnetic constituents with novel ternary nanostructure leads to their enhanced microwave absorbing properties. Furthermore, the addition of rGO with much lower density than CI reduces the density of composites, which makes the CI/rGO/PVP ternary composites a very promising material in microwave absorbing application.

Nonlinear optical vibrations of single-walled carbon nanotubes

We demonstrate the new specific phenomenon of the long-time resonant energy exchange in the carbon nanotubes (CNTs) in the two optical branches - the Circumferential Flexure Mode (CFM) and Radial Btreathing Mode (RBM). It is shown that the modified nonlinear Schrödinger equation, obtained in the framework of nonlinear elastic thin shell theory, allows to describe the CNT nonlinear dynamics connected with considered frequency bands. Comparative analysis of the oscillations of the CFM and RBM branches shows the principal difference between nonlinearity effects. If the nonlinear resonant interaction of the low-frequency modes in the CFM branch leads to the energy capture in the some domain of the CNT, the same interaction in the RBM branch does not appear any tendency to the energy localization. The reason of such a distinction is the difference of the non-linear terms in the equations of motion. If the CFMs are specified by the soft power nonlinearity, the RBM dynamics is determined by the hard gradient nonlinearity. Moreover, in contrast to CFM the importance of nonlinearity in the case of RBM oscillations decreases with increasing of the length to radius ratio. The numerical integration of the thin shell theory equations confirms the results of the analytical study.

Coaxial multi-interface hollow Ni-Al2O3-ZnO nanowires tailored by atomic layer deposition for selective-frequency absorptions

In this work, atomic layer deposition (ALD) was employed to fabricate coaxial multi-interface hollow Ni-Al2O3-ZnO nanowires. The morphology, microstructure, and ZnO shell thickness dependent electromagnetic and microwave absorbing properties of these Ni-Al2O3-ZnO nanowires were characterized. Excellent microwave absorbing properties with a minimum reflection loss (RL) of approximately–50 dB at 9.44 GHz were found for the Ni-Al2O3-100ZnO nanowires, which was 10 times of Ni-Al2O3 nanowires. The microwave absorption frequency could be effectively varied by simply adjusting the number of ZnO deposition cycles. The absorption peaks of Ni-Al2O3-100ZnO and Ni-Al2O3-150ZnO nanowires shifted of 5.5 and 6.8 GHz towards lower frequencies, respectively, occupying one third of the investigated frequency band. The enhanced microwave absorption arose from multiple loss mechanisms caused by the unique coaxial multi-interface structure, such as multi-interfacial polarization relaxation, natural and exchange resonances, as well as multiple internal reflections and scattering. These results demonstrate that the ALD method can be used to realize tailored nanoscale structures, making it a highly promising method for obtaining highefficiency microwave absorbers, and opening a potentially novel route for frequency adjustment and microwave imaging fields.

Structural, magnetic and microwave absorption properties of Ni-doped ZnO nanofibers

ZnO nanofibers (NixZn(1 − x)O with x = 0.03, 0.05, 0.07, 0.09) have been prepared by electrospinning method. The structural, morphological, static magnetic properties and microwave absorption properties are investigated in detail. The as-prepared samples show hexagonal wurtzite structure. However, the lattice constants decrease with the increase of Ni doping cotent, which result in the shrunk of the diameter of nanofibers. The static magnetic properties and microwave absorption properties can be tuned by varying the Ni content. The maximum saturation magnetization is obtained when x = 0.07 due to cation percolation threshold. The dielectric loss properties could be attributed to the dipole polarizations and interface polarization. The magnetic loss properties are mainly caused by natural resonance and exchange resonance. In addition, the networks of NixZn(1 − x)O nanofibers also benefit dissipating electromagnetic energy. The refelection loss (RL) of Ni0.07Zn0.93O nanofibers reaches −2.7 dB at 7.6 GHz and the electromagnetic wave absorption less than −2 dB is found to reach 3.1 GHz for an absorber thickness of 4.5 mm.

Coupling of three-spin qubits to their electric environment

We investigate the behavior of qubits consisting of three electron spins in double and triple quantum dots subject to external electric fields. Our model includes two independent bias parameters, $\ensuremath{\varepsilon}$ and ${\ensuremath{\varepsilon}}_{M}$, which both couple to external electromagnetic fields and can be controlled by gate voltages applied to the quantum dot structures. By varying these parameters, one can switch the qubit type by shifting the energies in the single quantum dots, thus changing the electron occupancy in each dot. Starting from the asymmetric resonant exchange qubit with a (2,0,1) and (1,0,2) charge admixture, one can smoothly cross over to the resonant exchange qubit with a detuned (1,1,1) charge configuration, and to the exchange-only qubit with the same charge configuration but equal energy levels down to the hybrid qubits with (1,2,0) and (0,2,1) charge configurations. Here, $(l,m,n)$ describes a configuration with $l$ electrons in the left dot, $m$ electrons in the center dot, and $n$ electrons in the right dot. We first focus on random electromagnetic field fluctuations, i.e., ``charge noise,'' at each quantum dot resulting in dephasing of the qubit, and we provide a complete map of the resulting dephasing time as a function of the bias parameters. We pay special attention to the so-called sweet spots and double sweet spots of the system, which are least susceptible to noise. In the second part, we investigate the coupling of the qubit system to the coherent quantized electromagnetic field in a superconducting strip-line cavity, and we also provide a complete map of the coupling strength as a function of the bias parameters. We analyze the asymmetric qubit-cavity coupling via $\ensuremath{\varepsilon}$ and the symmetric coupling via ${\ensuremath{\varepsilon}}_{M}$.

Temperature and magnetic field dependence ofrare−earth↔ironexchange resonance mode in a magnetic oxide studied with femtosecond magneto-optical Kerr effect

In magnetic materials, the exchange is the strongest quantum interaction due to the Pauli exclusion principle. For that reason it can induce high-frequency modes ${f}_{\mathrm{exch}}$ of the magnetization precession. In this work we investigate these modes over a wide range of temperatures ($50--300\phantom{\rule{0.16em}{0ex}}\text{K}$) and magnetic fields up to $10T$ in a bismuth-doped garnet with perpendicular magnetic anisotropy by performing femtosecond magneto-optical pump-probe experiments. Near the compensation temperature ${T}_{M}$ the divergence of $1/{f}_{\mathrm{exch}}(T)$ allows identifying unambiguously ${f}_{\mathrm{exch}}$ with the rare-earth $\ensuremath{\leftrightarrow}$ iron exchange mode. In addition, at low temperature ${f}_{\mathrm{exch}}$ is independent of the field as usually observed. In contrast, we find that near ${T}_{M},\phantom{\rule{0.28em}{0ex}}{f}_{\mathrm{exch}}$ decreases linearly with an increasing magnetic field. This behavior is explained in the context of the ferromagnetic resonance theory by including the perturbation term linear in the external applied field ${H}_{\mathrm{ext}}$.

Dynamics of vector rogue waves in a fiber laser with a ring cavity

A pulse–pulse interaction that leads to rogue wave (RW) generation in lasers was previously attributed either to soliton–soliton or soliton–dispersive-wave interaction. The beating between polarization modes in the absence of a saturable absorber causes similar effects. Accounting for these polarization modes in a laser resonator is the purpose of the distributed vector model of laser resonators. Furthermore, high pump power, high amplitude, and short pulse duration are not necessary conditions to observe pulse attraction, repulsion, and collisions and the resonance exchange of energy between among them. The regimes of interest can be tuned just by changing the birefringence in the cavity with the pump power slightly higher than the laser threshold. This allows the observation of a wide range of RW patterns in the same experiment, as well as to classify them. The dynamics of the interaction between pulses leads us to the conclusion that all of these effects occur due to nonlinearity induced by the inverse population in the active fiber as well as an intrinsic nonlinearity in the passive part of the cavity. Most of the mechanisms of pulse–pulse interaction were found to be mutually exclusive. This means that all the observed RW patterns, namely, the “lonely,” “twins,” “three sisters,” and “cross,” are probably different cases of the same process.

Dynamics of vector rogue waves in a fiber laser with a ring cavity

A pulse–pulse interaction that leads to rogue wave (RW) generation in lasers was previously attributed either to soliton–soliton or soliton–dispersive-wave interaction. The beating between polarization modes in the absence of a saturable absorber causes similar effects. Accounting for these polarization modes in a laser resonator is the purpose of the distributed vector model of laser resonators. Furthermore, high pump power, high amplitude, and short pulse duration are not necessary conditions to observe pulse attraction, repulsion, and collisions and the resonance exchange of energy between among them. The regimes of interest can be tuned just by changing the birefringence in the cavity with the pump power slightly higher than the laser threshold. This allows the observation of a wide range of RW patterns in the same experiment, as well as to classify them. The dynamics of the interaction between pulses leads us to the conclusion that all of these effects occur due to nonlinearity induced by the inverse population in the active fiber as well as an intrinsic nonlinearity in the passive part of the cavity. Most of the mechanisms of pulse–pulse interaction were found to be mutually exclusive. This means that all the observed RW patterns, namely, the “lonely,” “twins,” “three sisters,” and “cross,” are probably different cases of the same process.

Electromagnetic loss properties of ZnO nanofibers

ZnO nanofibers were fabricated by electrospinning method. The morphology and microstructure of the as-prepared ZnO nanofibers were studied in details. The ZnO nanofibers showed pure polycrystalline phase with the hexagonal wurtzite structure. The average diameter of the ZnO nanofibers, calcined at 550 °C, was around 140 nm. Moreover, the electromagnetic loss properties of the as-prepared ZnO nanofibers were investigated. The mechanism of dielectric loss could be attributed to the electric dipolar polarization and interface polarization. The mechanism of magnetic loss properties were mainly caused by natural resonance and exchange resonance. The networks of ZnO nanofibers also facilitated dissipating electromagnetic energy. The dielectric loss factor tanδe was around 0.06085 and the magnetic loss factor tanδμ was approximate 0.04095. The as-prepared ZnO nanofiber exhibited excellent electromagnetic loss properties and it could be usd as a potential candidate for lightweight microwave absorption material.

Fast control of semiconductor qubits beyond the rotating-wave approximation

We present a theoretical study of single-qubit operations by oscillatory fields on various semiconductor platforms. We explicitly show how to perform faster gate operations by going beyond the universally-used rotating wave approximation (RWA) regime, while using only two sinusoidal pulses. No complicated pulse shaping or optimal control sequences are required. We first show for specific published experiments how much error is currently incurred by implementing pulses designed using standard RWA. We then show that an even modest increase in gate speed would cause problems in using RWA for gate design in the singlet-triplet (ST) and resonant-exchange (RX) qubits. We discuss the extent to which analytically keeping higher orders in the perturbation theory would address the problem. More strikingly, we give a new prescription for gating with strong coupling far beyond the RWA regime. We perform numerical calculations for the phases and the durations of two consecutive pulses to realize the key Hadamard and $\frac{\pi}{8}$ gates with coupling strengths up to several times the qubit splitting. Working in this manifestly non-RWA regime, the gate operation speeds up by two to three orders of magnitude.

Enhanced microwave absorption properties of NiFe2O4 nanocrystal deposited reduced graphene oxides

In this work, the NiFe2O4–reduced graphene oxide (NiFe2O4–rGO) was achieved via a one-step hydrothermal method. The microstructure, permittivity and permeability and electromagnetic attenuation properties of NiFe2O4–rGO are investigated. The minimum reflection loss reaches −46.8 dB at d = 4.8 mm. The introduction of NiFe2O4 nanocrystals enhances electromagnetic attenuation due to the synergetic effect of dielectric and magnetic loss as well as the enhanced exchange resonance. It is believed that the deposition of magnetic nanocrystals is a way to generate light-weight and high-efficient microwave absorbers. The NiFe2O4–rGO is a promising candidate for electromagnetic attenuation in various fields.

Resonance dynamics of kinks in the sine-Gordon model with impurity, external force and damping

We study the resonance dynamics of the sine-Gordon equation kinks with a point impurity. We consider the possibility of localized nonlinear waves generation on the impurities. By using analytical and numerical methods we show that the damping and external force counteract the development of kink resonant reflection from the attracting impurity. However, the underlying cause–a resonant energy exchange between solitons–still occurs.

Modes of Intersubjective Address in The Central Character (1977) and Our Marilyn (1987)

This article examines the use of intersubjective modes of address in Canadian feminist experimental film between 1979 and 1987. It compares Patricia Gruben’s The Central Character (1979) and Brenda Longfellow’s Our Marilyn (1987), noting how the use of experimental forms of address in both affectively blur the distinction between diegetic and non-diegetic space, unsettling the certainty of the spectator’s viewing position. The article counters the reading of feminist avant-garde film from this decade as being engaged in disruptive practices. While dissonance and dislocation are a part of the history of feminist experimental film aesthetics, the article argues it is equally necessary to map moments of resonance and intersubjective exchange in these films. Gruben and Longfellow’s experiments with cinematic address are framed as important interventions into dominant forms of representation that expand the range of possibilities for both the image of woman onscreen and the feminist spectator in the audience.

Characterization of an exchange-based two-qubit gate for resonant exchange qubits

Resonant exchange qubits are a promising addition to the family of experimentally implemented encodings of single qubits using semiconductor quantum dots. We have shown previously that it ought to be straightforward to perform a CPHASE gate between two resonant exchange qubits with a single exchange pulse. This approach uses energy gaps to suppress leakage rather than conventional pulse sequences. In this paper we present analysis and simulations of our proposed two-qubit gate subject to charge and Overhauser field noise at levels observed in current experiments. Our main result is that we expect implementations of our two-qubit gate to achieve high fidelities, with errors at the percent level and gate times comparable to single-qubit operations. As such, exchange-coupled resonant exchange qubits remain an attractive approach for quantum computing.

Facile Synthesis of Fe3O4/GCs Composites and Their Enhanced Microwave Absorption Properties.

Graphene has good stability and adjustable dielectric properties along with tunable morphologies, and hence can be used to design novel and high-performance functional materials. Here, we have reported a facile synthesis method of nanoscale Fe3O4/graphene capsules (GCs) composites using the combination of catalytic chemical vapor deposition (CCVD) and hydrothermal process. The resulting composite has the advantage of unique morphology that offers better synergism among the Fe3O4 particles as well as particles and GCs. The microwave-absorbing characteristics of developed composites were investigated through experimentally measured electromagnetic properties and simulation studies based on the transmission line theory, explained on the basis of eddy current, natural and exchange resonance, as well as dielectric relaxation processes. The composites bear minimum RL value of -32 dB at 8.76 GHz along with the absorption bandwidth range from 5.4 to 17 GHz for RL lower than -10 dB. The better performance of the composite based on the reasonable impedance characteristic, existence of interfaces around the composites, and the polarization of free carriers in 3D GCs that make the as-prepared composites capable of absorbing microwave more effectively. These results offer an effective way to design high-performance functional materials to facilitate the research in electromagnetic shielding and microwave absorption.

Non-thermal optical excitation of terahertz-spin precession in a magneto-optical insulator

We demonstrate non-thermal ultrafast laser excitation of spin precession with THz frequency in Gd-Bi-substituted iron garnet via the inverse Faraday effect. The modulation of THz precession by about 60 GHz below the compensation temperature of magnetic moment was observed. The THz frequency precession was caused by the exchange resonance between the Gd and Fe sublattices; we attributed the low-frequency modulation to dielectric resonance mode with a magnetic contribution. We demonstrate the possibility of polarization-sensitive control of spin precession under THz generation by laser pulses, helping to develop high-speed magneto-optical devices.

Properties of Hf-Doped Bi&lt;sub&gt;1.5&lt;/sub&gt;Zn&lt;sub&gt;0.92&lt;/sub&gt;Nb&lt;sub&gt;1.5&lt;/sub&gt;O&lt;sub&gt;6.92&lt;/sub&gt; Ceramic Varicaps

The hafnium doping effects on the performance of the Bi1.5Zn0.92Nb1.5O6.92 (BZN) varicaps are explored by means of impedance and signal power spectroscopes in the range of 10–1800 and 1000–3000 MHz, respectively. The Hf content that was varied in accordance with the Bi1.5Zn0.92–2 x Hf x Nb1.5O6.92 formalism was observed to reach the solubility limit at the Hf content of 0.06. The free carrier concentration in the devices systematically increased with the increasing Hf content. The impedance spectral analysis revealed a series and parallel resonance exchange above 1000 MHz. The critical frequencies of resonance are observed to shift from 1638 to 1585 and reach 1476 MHz as the Hf content increases from 0.00 to 0.03 and reaches 0.06, respectively. It was also observed that the hafnium doping significantly increases the respective dielectric constant of BZN from 268 to 290 and to 470. In addition to the negative dielectric property that is useful in applications where the cancelation of parasitic capacitance is needed, the wave power spectral analysis revealed the microwave band-reject filter properties with the respective notch frequencies of 1580, 1845, and 2040 MHz. While the undoped ceramic filters can detect the signals of power down to 40 nW, the doped ones are functional for the signals of microwatt power.

Erratum: Asymmetric resonant exchange qubit under the influence of electrical noise [Phys. Rev. B91, 235411 (2015)

Received 10 December 2015DOI:https://doi.org/10.1103/PhysRevB.92.239905©2015 American Physical Society

Long distance coupling of resonant exchange qubits

We investigate the effectiveness of a microwave cavity as a mediator of interactions between two resonant exchange (RX) qubits in semiconductor quantum dots (QDs) over long distances, limited only by the extension of the cavity. Our interaction model includes the orthonormalized Wannier orbitals constructed from Fock-Darwin states under the assumption of a harmonic QD confinement potential. We calculate the qubit-cavity coupling strength in a Jaynes Cummings Hamiltonian, and find that dipole transitions between two states with an asymmetric charge configuration constitute the relevant RX quoit-cavity coupling mechanism. The effective coupling between two RX qubits in a shared cavity yields a universal two-qubit iSWAP-gate with gate times on the order of nanoseconds over distances on the order of up to a millimeter.

From raw data to data-analysis for magnetic resonance spectroscopy – the missing link: jMRUI2XML

BackgroundMagnetic resonance spectroscopy provides metabolic information about living tissues in a non-invasive way. However, there are only few multi-centre clinical studies, mostly performed on a single scanner model or data format, as there is no flexible way of documenting and exchanging processed magnetic resonance spectroscopy data in digital format. This is because the DICOM standard for spectroscopy deals with unprocessed data.This paper proposes a plugin tool developed for jMRUI, namely jMRUI2XML, to tackle the latter limitation. jMRUI is a software tool for magnetic resonance spectroscopy data processing that is widely used in the magnetic resonance spectroscopy community and has evolved into a plugin platform allowing for implementation of novel features.ResultsjMRUI2XML is a Java solution that facilitates common preprocessing of magnetic resonance spectroscopy data across multiple scanners. Its main characteristics are: 1) it automates magnetic resonance spectroscopy preprocessing, and 2) it can be a platform for outputting exchangeable magnetic resonance spectroscopy data. The plugin works with any kind of data that can be opened by jMRUI and outputs in extensible markup language format. Data processing templates can be generated and saved for later use.The output format opens the way for easy data sharing- due to the documentation of the preprocessing parameters and the intrinsic anonymization - for example for performing pattern recognition analysis on multicentre/multi-manufacturer magnetic resonance spectroscopy data.ConclusionsjMRUI2XML provides a self-contained and self-descriptive format accounting for the most relevant information needed for exchanging magnetic resonance spectroscopy data in digital form, as well as for automating its processing. This allows for tracking the procedures the data has undergone, which makes the proposed tool especially useful when performing pattern recognition analysis. Moreover, this work constitutes a first proposal for a minimum amount of information that should accompany any magnetic resonance processed spectrum, towards the goal of achieving better transferability of magnetic resonance spectroscopy studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12859-015-0796-5) contains supplementary material, which is available to authorized users.