Transverse Coupling Research Articles

High-Fidelity Controlled-Z Gate with Maximal Intermediate Leakage Operating at the Speed Limit in a Superconducting Quantum Processor.

Simple tuneup of fast two-qubit gates is essential for the scaling of quantum processors. We introduce the sudden variant (SNZ) of the net zero scheme realizing controlled-Z (CZ) gates by flux control of transmon frequency. SNZ CZ gates realized in a multitransmon processor operate at the speed limit of transverse coupling between computational and noncomputational states by maximizing intermediate leakage. Beyond speed, the key advantage of SNZ is tuneup simplicity, owing to the regular structure of conditional phase and leakage as a function of two control parameters. SNZ is compatible with scalable schemes for quantum error correction and adaptable to generalized conditional-phase gates useful in intermediate-scale applications.

Combined effect of chromaticity and feedback on transverse head-tail instability

The resonant interaction of a bunched particle beam with short-range wakefields is the cause of head-tail instability, which is a major limitation for single-bunch beam intensity in circular accelerators. There are several processes that suppress this type of instability, such as fast chromatic damping and Landau damping due to machine nonlinearity. Beam-based feedback systems (transverse dampers) provide active suppression of the beam oscillations. The combined effect of the transverse dampers and chromaticity is discussed in this article. A brief overview of theoretical and experimental studies of the head-tail instability and its mitigation is presented. Results of experimental studies of the transverse mode coupling carried out at National Synchrotron Light Source-II are compared with the theoretical model.

Study on the anti-correlated painting injection scheme for the Rapid Cycling Synchrotron of the China Spallation Neutron Source

In the rapid cycling synchrotron of the China Spallation Neutron Source, the anti-correlated painting was adopted for the design scheme of the injection system. In the beam commissioning, with the optimization of the anti-correlated painting, the injection beam loss has been well controlled and the injection efficiency has exceeded 99%. Combined with other aspects of adjustments, the beam power on the target has reached 50 kW. In this paper, we have studied the injection optimization in the beam commissioning. Compared to the simulation results of the design scheme, the transverse beam distribution, transverse coupling effect and beam loss of the anti-correlated painting in the beam commissioning are somewhat different. Through the machine studies, we have carefully analyzed these differences and studied their reasons.

Imaginary tune split and repulsion single-bunch instability mechanism in the presence of a resistive transverse damper and its mitigation

A resistive transverse damper is often needed in particle accelerators operating with many bunches and it is usually very efficient as it can considerably reduce the necessary amount of nonlinearities needed to reach beam stability through Landau damping. In the CERN LHC for instance, the required current in the Landau octupoles is predicted to be reduced by an order of magnitude for zero chromaticity (for the beam and machine parameters used during the last year of Run 2, in 2018, this corresponded to $\ensuremath{\sim}2000\text{ }\text{ }\mathrm{A}$ without damper and $\ensuremath{\sim}200\text{ }\text{ }\mathrm{A}$ with damper, knowing that the maximum current available in the Landau octupoles is $\ensuremath{\sim}550\text{ }\text{ }\mathrm{A}$). However, a resistive transverse damper also destabilizes the single-bunch motion below the transverse mode coupling instability intensity threshold (for zero chromaticity), introducing a new kind of instability, which has been called ITSR instability (for imaginary tune split and repulsion). Until now, only one type of impedance-driven transverse coherent instability has been explained for a single bunch in a circular particle accelerator, at zero chromaticity and without a multiturn wake: the transverse mode coupling instability. A transverse mode coupling instability can also be observed in the presence of Landau damping, beam-beam, electron cloud or space charge. However, the ITSR instability exhibits a different mechanism, which is not due to mode coupling. The purpose of this article is to explain in detail both this new instability mechanism and its mitigation using a simplified analytical model, which has been carefully benchmarked, using the pyheadtail macroparticle tracking code, by Oeftiger (one of the code's developers).

Second-order modes of transverse oscillations in intense beams: Chernin’s matrix formalism versus Vlasov–Poisson equations

We study an intense space charge dominated beam in the realm of beam optics of particle accelerators. We assume an anisotropic beam with different external focussing constants and with different phase space emittances in the two transverse directions. We consider the root mean square moment equations of the beam with linear transverse coupling of particle motion ( $$x$$ and $$y$$ ). Magnetic focussing fields and the space charge Coulomb’s self-field forces are expressed in a matrix format and describe the governing equations for the beam outer envelope. By linearizing the equations, we investigate the collective response of ensemble of particles. This response is stated as coherent mode frequencies for the second-order even (envelope) and odd (tilting) oscillation modes of the beam cross section. We discuss the main features of the eigenfrequencies in detail. The approach known as Chernin’s matrix formalism is conceptually equivalent to the second-order moments of the full Vlasov–Poisson kinetic equation in four-dimensional phase space. We show that the relations obtained via matrix approach are in full agreement with the eigenfrequencies of transverse oscillations obtained by the linearized kinetic Vlasov–Poisson equations.

Enhancement of quantum correlations and a geometric phase for a driven bipartite quantum system in a structured environment

We study the role of driving in an initial maximally entangled state evolving under the presence of a structured environment in a weak and strong regime. We focus on the enhancement and degradation of maximal concurrence when the system is driven on and out of resonance for a general evolution, as well as the effect of adding a transverse coupling among the particles of the model. We further investigate the role of driving in the acquisition of a geometric phase for the maximally entangled state. As the model studied herein can be used to model experimental situations such as hybrid quantum classical systems feasible with current technologies, this knowledge can aid the search for physical setups that best retain quantum properties under dissipative dynamics.

A coherent harmonic generation method for producing femtosecond coherent radiation in a laser plasma accelerator based light source.

The electron beam generated in laser plasma accelerators (LPAs) has two main initial weaknesses - a large beam divergence (up to a few milliradians) and a few percent level energy spread. They reduce the beam brightness and worsen the coherence of the LPA-based light source. To achieve fully coherent radiation, several methods have been proposed for generating strong microbunching on LPA beams. In these methods, a seed laser is used to induce an angular modulation into the electron beam, and the angular modulation is converted into a strong density modulation through a beamline with nonzero longitudinal position and transverse angle coupling. In this paper, an alternative method to generate microbunching into the LPA beam by using a seed laser that induces an energy modulation and transverse-longitudinal coupling beamlines that convert the energy modulation into strong density modulation is proposed. Compared with the angular modulation methods, the proposed method can use more than one order of magnitude lower seed laser power to achieve similar radiation performance. Simulations show that with the proposed method a coherent pulse of a few microjoules pulse energy and femtosecond duration can be generated with a typical LPA beam.

Transversal Coupled Triple-Mode Spherical Resonator-Based Bandpass Filters

In this letter, we present an innovative filter configuration employing transversal coupled triple-mode spherical resonators while capable of realizing transmission zeros (TZs). Transversal coupling involves simultaneous source and load-controlled couplings to all the three modes of the spherical resonator. Spherical resonators inherently have very large quality factor (Qu) and exhibit a farther spurious response thus yielding bandpass filters (BPFs) with lower insertion loss and wider spurious-free window. The design methodology for transversal coupling is explained and is employed for designing a third-order bandpass filter with TZs. In addition, a sixth-order bandpass filter using cascaded trisection is also presented. A third-order BPF with symmetric TZs is fabricated for verifying proof of the concept. The filter designed at 6.545 GHz with a bandwidth of 120 MHz has an insertion loss better than 0.1 dB and a spurious-free window better than 1.7 GHz. The proposed filter promises to be useful in aerospace applications that demand high Qu, low volume, and wider spurious-free window.

Intrabunch motion

Impedance-driven (but not only) coherent beam instabilities are usually studied analytically with the linearized Vlasov equation, ending up with an eigenvalue system to solve. The eigenvalues describe the beam oscillation mode-frequency shifts, leading in particular to intensity thresholds defined by the longitudinal mode coupling instability in the longitudinal plane and by the transverse mode coupling instability in the transverse plane in the absence of chromaticity. This can be directly compared to measurements in particular for the lowest modes and in the absence of tune spread. In the presence of nonlinearities or when higher-order modes are involved, this becomes quite difficult, if not impossible, and the coupling between the modes cannot be directly measured (or simulated) anymore. Another important observable is the intrabunch motion, which can be also accessed analytically thanks to the eigenvectors. To the author's knowledge, until now, the intrabunch signal has only been explained theoretically for independent longitudinal or transverse beam oscillation modes, i.e., when the bunch intensity is sufficiently low compared to the mode coupling threshold. It was never explained theoretically in detail when two (or more) modes are involved. For instance, no answers were already given to these questions: is (are) there some fixed point(s) when the transverse mode coupling instability starts? If yes, where is it (are they)? And what happens in the presence of mode decoupling? Any number of modes can be treated with the general approach discussed in this paper, which is based on the galactic Vlasov solver (which was previously successfully benchmarked against the pyheadtail macroparticle tracking code as concerns the beam oscillation mode-frequency shifts). However, to be able to clearly see what happens when the bunch intensity is increased, the simple case of two modes is discussed in detail. The purpose of this paper is to describe the different regimes, below, at, above the transverse mode coupling instability and also after the mode decoupling (as it happens sometimes), using a simple analytical model (where two modes are considered together), which helps to really understand what happens at each step. Better characterizing an instability is the first step before trying to find appropriate mitigation measures and push the performance of a particle accelerator. The evolution of the intrabunch motion with intensity is a fundamental observable with high-intensity high-brightness beams.

Universal Nonadiabatic Control of Small-Gap Superconducting Qubits

Resonant transverse driving of a two-level system as viewed in the rotating frame couples two degenerate states at the Rabi frequency, an amazing equivalence that emerges in quantum mechanics. While spectacularly successful at controlling natural and artificial quantum systems, certain limitations may arise (e.g., the achievable gate speed) due to non-idealities like the counter-rotating term. Here, we explore a complementary approach to quantum control based on non-resonant, non-adiabatic driving of a longitudinal parameter in the presence of a fixed transverse coupling. We introduce a superconducting composite qubit (CQB), formed from two capacitively coupled transmon qubits, which features a small avoided crossing -- smaller than the environmental temperature -- between two energy levels. We control this low-frequency CQB using solely baseband pulses, non-adiabatic transitions, and coherent Landau-Zener interference to achieve fast, high-fidelity, single-qubit operations with Clifford fidelities exceeding $99.7\%$. We also perform coupled qubit operations between two low-frequency CQBs. This work demonstrates that universal non-adiabatic control of low-frequency qubits is feasible using solely baseband pulses.

Critical Fermi surfaces in generic dimensions arising from transverse gauge field interactions

We study critical Fermi surfaces in generic dimensions arising from coupling finite-density fermions with transverse gauge fields, by applying the dimensional regularization scheme developed previously [Phys. Rev. B 92, 035141 (2015)]. We consider the cases of $U(1)$ and $U(1)\times U(1)$ transverse gauge couplings, and extract the nature of the renormalization group (RG) flow fixed points as well as the critical scalings. Our analysis allows us to treat a critical Fermi surface of a generic dimension $m$ perturbatively in an expansion parameter $\epsilon =\left (2-m \right ) /\left (m+1 \right).$ One of our key results is that although the two-loop corrections do not alter the existence of an RG flow fixed line for certain $U(1)\times U(1)$ theories, which was identified earlier for $m=1$ at one-loop order, the third-order diagrams do. However, this fixed line feature is also obtained for $m>1$, where the answer is one-loop exact due to UV/IR mixing.

Magnetoacoustic Resonance to Probe Quadrupole–Strain Coupling in a Diamond Nitrogen-Vacancy Center as a Spin-Triplet System

A theory of magnetoacoustic resonance is proposed to measure quadrupole-strain couplings in a spin-triplet state with the $C_{3v}$ point group symmetry, considering the spin-strain interaction in a diamond nitrogen-vacancy (NV) center. Based on the Floquet theory, we demonstrate how the single- and two-phonon transition probabilities depend on the change in the longitudinal and transverse quadrupole couplings, which can be controlled by rotating an applied magnetic field, around the threefold axis. The obtained quadrupole dynamics results are useful for realizing mechanical or ac strain-control of the NV spin as an alternative to the conventional magnetic control by spin resonance.

Turing Patterning in Stratified Domains

Reaction–diffusion processes across layered media arise in several scientific domains such as pattern-forming E. coli on agar substrates, epidermal–mesenchymal coupling in development, and symmetry-breaking in cell polarization. We develop a modeling framework for bilayer reaction–diffusion systems and relate it to a range of existing models. We derive conditions for diffusion-driven instability of a spatially homogeneous equilibrium analogous to the classical conditions for a Turing instability in the simplest nontrivial setting where one domain has a standard reaction–diffusion system, and the other permits only diffusion. Due to the transverse coupling between these two regions, standard techniques for computing eigenfunctions of the Laplacian cannot be applied, and so we propose an alternative method to compute the dispersion relation directly. We compare instability conditions with full numerical simulations to demonstrate impacts of the geometry and coupling parameters on patterning, and explore various experimentally relevant asymptotic regimes. In the regime where the first domain is suitably thin, we recover a simple modulation of the standard Turing conditions, and find that often the broad impact of the diffusion-only domain is to reduce the ability of the system to form patterns. We also demonstrate complex impacts of this coupling on pattern formation. For instance, we exhibit non-monotonicity of pattern-forming instabilities with respect to geometric and coupling parameters, and highlight an instability from a nontrivial interaction between kinetics in one domain and diffusion in the other. These results are valuable for informing design choices in applications such as synthetic engineering of Turing patterns, but also for understanding the role of stratified media in modulating pattern-forming processes in developmental biology and beyond.

Robust Weyl points in a one-dimensional superlattice with transverse spin-orbit coupling

Weyl points, synthetic magnetic monopoles in the 3D momentum space, are the key features of topological Weyl semimetals. The observation of Weyl points in ultracold atomic gases usually relies on the realization of high-dimensional spin-orbit coupling (SOC) for two pseudospin states (% \textit{i.e.,} spin-1/2), which requires complex laser configurations and precise control of laser parameters, thus has not been realized in experiment. Here we propose that robust Wely points can be realized using 1D triple-well superlattices (spin-1/three-band systems) with 2D transverse SOC achieved by Raman-assisted tunnelings. The presence of the third band is responsible to the robustness of the Weyl points against system parameters (e.g., Raman laser polarization, phase, incident angle, etc.). Different from a spin-1/2 system, the non-trivial topology of Weyl points in such spin-1 system is characterized by both the spin vector and tensor textures, which can be probed using momentum-resolved Rabi spectroscopy. Our proposal provides a simple yet powerful platform for exploring Weyl physics and related high-dimensional topological phenomena using high pseudospin ultracold atoms.

Elementary quantum gates between long-distance qubits mediated by a resonator

We propose a scheme to realize Controlled-NOT, Controlled-V, Controlled- $$V^{\dag }$$ gate based on the indirect coupling of two qubits which are coupled to a common resonator. Based on the state-of-the-art controllability of longitudinal and transverse coupling between a qubit and a resonator, we let the control qubit couple to the resonator longitudinally and the target qubit couple to the resonator transversely. One can get the fidelity of these gates (as well as the synthesized Toffoli gate) over 99% within effective gate timescales. The proposed gate scheme is possible for the experimental setups where the effective qubit–resonator coupling strength is far bigger than the cavity decay rate and the dephasing rate of the qubits and applicable to quantum circuit synthesizing and long-distance qubit interaction.

Effect of aerodynamic force change caused by car-body rolling on train overturning safety under strong wind conditions

Understanding the relationship between car-body vibration and train aerodynamic forces is very important for developing a reasonable operation plan when the train passes through the complex terrain under strong wind conditions. In this study, car-body vibration under strong wind conditions was initially investigated with a full-scale test. Then the train aerodynamic forces for different rotation configurations with a train speed of 250 km/h and a wind speed of 25 m/s were further studied using a Computational Fluid Dynamics simulation. The results revealed that the car-body vibration was primarily a low-frequency and large-amplitude rolling and transverse coupling motion in windy conditions, and the roll angle of the car-body with respect to the bogie frame was greater than that of the bogie frame with respect to the track. The train aerodynamic force coefficients are sensitive to the car-body rolling motion in windy conditions. When the car-body rolling from the windward side to the leeward side, the significant reduction in the negative pressure at the bottom of the car-body was the dominant reason for the train lift force increase, and the effect of the aerodynamic force change caused by car-body rolling on the train overturning risk was not significant.

MgFe2O4/(Ba0·85Ca0.15) (Zr0·1Ti0.9)O3 lead free ceramic composite: A study on multiferroic and magnetoelectric coupling properties at room temperature

MgFe2O4 (MFO) and (Ba0·85Ca0.15) (Zr0·1Ti0.9)O3 (BCZT) was prepared by solid state route and are found to be ferromagnetic and ferroelectric at room temperature respectively. MFO/BCZT composite (50:50 M concentration of MFO and BCZT) was also prepared by solid state route. Multiferroic properties of MFO/BCZT ceramic composite were investigated. Scanning electron micrograph confirms the distribution of small grains of MFO around large grain of BCZT for proper surface interaction. MFO/BCZT composite exhibits saturated magnetization of 12 emu/gm, which reduce to 10 emu/gm on electrical poling at 2.5 kV/cm indicating magneto-electric coupling between MFO and BCZT through interface interaction. The composite also exhibits proper ferroelectric polarization, which is confirmed from I–V characteristic plot (occurrence of double minima as that of proper ferroelectric). The transverse magnetoelectric coupling coefficient (αV31) for this composite is found to be 7.97 mVcm−1Oe−1 at 10 kHz. MFO/BCZT ceramic composite exhibit multiferroic and magnetoelectric coupling properties for 50:50 M concentration at room temperature may be suitable for device applications.

Considerations about the friction inside on a transversal coupling

The paper presents, starting from some kinematic aspects as rotations and translations between the Oldham coupling parts, some kinematic equations useful in determining of intermediary element position depending by the transversal misalignments. Then, using the inside translational movements between parts, the friction coefficient between adequate materials to be used are studied. The friction which appears between the coupling parts has an important influence on their dynamic behaviour, wear and lifetime. The most significant friction and also wear is given by the translational movements between parts. Due to this, the study of the friction between some materials to be used in coupling manufacturing is required, but also difficult because of some particularities, as reduced parts translational movements for reduced transversal misalignments between shafts, or the alternative translational movement in translational joints. In the paper final part the results and conclusions are presented.

Direction dependent strong magnetoelectric coupling in La0.7Ba0.3MnO3 embedded poly(vinylidenefluoride-co-trifluoroethylene) flexible nano-composite films at room temperature

Magnetoelectric coupling of La0.7Ba0.3MnO3/ poly(vinylidenefluoride-co-trifluoroethylene) nano-composite (0–3) films were studied by varying the volume fraction of La0.7Ba0.3MnO3 in polymer matrix for non-poled and electrically poled conditions. The transverse magnetoelectric coupling coefficient (αV31) value is larger compared to αV33 (logitudinal coupling coeffcient) for composite films. The maximum value of αV31 is found to be 121.44 mVcm−1Oe−1 for poled composite films (0.5% La0.7Ba0.3MnO3 volume fraction) at 10 kHz. These films generate a self-biased voltage 9.1 mV on application of 25Oe alternating magnetic field (Hac). The dependence of αV31 of these films on static magnetic field (Hdc), Hac and frequency is also reported.

Design of spatially varying electrical poling for enhanced piezoelectricity in Pb(Mg1/3Nb2/3)O3–0.35PbTiO3

Improvement in operating characteristics of piezoelectric materials, one of the most extensively used dielectric materials, is a major focus of research among materials scientists. Present work puts forward, a novel approach for achieving enhanced piezoelectricity in ferroelectric materials by manipulating electrode placement during poling. Three unique poling configurations, abbreviated as PC1, PC2, and PC3 are developed for exploiting the dependence of effective piezoelectric properties on spatially varying poling direction. Finite element method based numerical simulations are performed to evaluate the electric field distribution, poling direction, and their effect on effective piezoelectric coupling coefficients of PMN–0.35PT (Pb(Mg1/3Nb2/3)O3–0.35PbTiO3) piezoelectric ceramic. A two-phase solution process is developed to evaluate the local orientation of dipoles for each poling configuration and subsequently computing effective piezoelectric properties of the material in an average sense. Parametric studies are carried out to analyze the effect of aspect ratio R of sample and electrode to sample length ratio, r on effective piezoelectric properties. PC1 yields an increase of up to 135% in the magnitude of the transverse coupling coefficient $$({e}_{31}^{eff})$$ and an 8% increase in effective longitudinal coupling coefficient $$({e}_{33}^{eff})$$ while PC2 is observed to exhibit a maximum enhancement of 164% in the magnitude of $${e}_{31}^{eff}$$ and 11.2% in the magnitude of $${e}_{33}^{eff}$$ . PC3, presented as a special case, yields zero values of piezoelectric coefficients in an average sense but can result in a highly elevated net output for bending applications, owing to favorable spatial variation in stresses and associated piezoelectric coefficients.