Tunneling Dynamics Research Articles

Quantum tunneling dynamics of an interacting Bose-Einstein condensate through a Gaussian barrier

The transmission of an interacting Bose-Einstein condensate incident on a repulsive Gaussian barrier is investigated through numerical simulation. The dynamics associated with interatomic interactions are studied across a broad parameter range not previously explored. Effective 1D Gross-Pitaevskii equation (GPE) simulations are compared to classical Boltzmann-Vlasov equation (BVE) simulations in order to isolate purely coherent matterwave effects. Quantum tunneling is then defined as the portion of the GPE transmission not described by the classical BVE. An exponential dependence of transmission on barrier height is observed in the purely classical simulation, suggesting that observing such exponential dependence is not a sufficient condition for quantum tunneling. Furthermore, the transmission is found to be predominately described by classical effects, although interatomic interactions are shown to modify the magnitude of the quantum tunneling. Interactions are also seen to affect the amount of classical transmission, producing transmission in regions where the non-interacting equivalent has none. This theoretical investigation clarifies the contribution quantum tunneling makes to overall transmission in many-particle interacting systems, potentially informing future tunneling experiments with ultracold atoms.

Parameters estimation methodology for the nonlinear rolling motion of finned cylindrical body

Identification of nonlinear roll dynamics of finned cylindrical bodies is a critical step when assessing free motion stability and trajectories of aerially dispensed munitions or decoys. In this paper the authors present a parameter estimation process that focuses on identifying nonlinear aerodynamic models that characterize the roll dynamics of a cylindrical body with wrap around fins using data from a series of dynamic wind tunnel tests. This is a three step approach that combines ordinary least squares, stepwise regression and the augmented output-error method, and it is initially tested using simulation data corrupted by white Gaussian noise and then applied to the wind tunnel data. Roll and roll rate dynamics were captured through a series of high angle of attack free-to-roll tests carried out at an airspeed of 35m/s corresponding to a Reynolds number of 800,000. The results and discussion in this paper demonstrate how simulation can be used to develop and mature a system identification routine followed by its assessment through wind tunnel test data. It is shown that high order nonlinear models with up to 14 terms can be parameterized to provide high levels of agreement with roll and roll rate dynamics observed in the dynamic wind tunnel tests.

Correlated tunneling dynamics of an ultracold Fermi-Fermi mixture confined in a double well

We unravel the correlated tunneling dynamics of a mass imbalanced few-body fermi-fermi mixture upon quenching the tilt of a double-well. The non-equilibrium dynamics of both species changes from Rabi-oscillations close to the non-interacting limit to a delayed tunneling dynamics for moderate interspecies repulsions. Considering strong interspecies interactions the lighter species experiences quantum self-trapping due to the heavier species which acts as an effective material barrier, while performing almost perfect Rabi-oscillations. The degree of entanglement, inherent in the system, is analyzed and found to be significant both at moderate and strong repulsions. To relate our findings with possible experimental realizations we simulate in-situ single-shot measurements and discuss how a sampling of such images dictates the observed dynamics. Finally, the dependence of the tunneling behavior on the mass ratio, the particle number in each species and the height of the barrier of the double-well is showcased.

Chemodynamics of Dwarf Galaxies under Ram Pressure

Abstract By implementing a dynamic wind tunnel model in a smoothed particle chemodynamic/hydrodynamic simulation suite, we have investigated the effects of ram pressure and tidal forces on dwarf galaxies similar to the Magellanic Clouds, within host galaxies with gas and dark matter halos that are varied, to compare the relative effects of tides and ram pressure. We concentrate on how the distributions of metals are affected by interactions. We find that while ram pressure and tidal forces have some effect on dwarf galaxy outflows, these effects do not produce large differences in the metal distributions of the dwarf disks, other than truncation in the outer regions in some cases, and that confinement from the host galaxy gas halo appears to be more significant than ram pressure stripping. We find that stochastic variations in the star formation rate can explain the remaining variations in disk metal properties. This raises questions on the cause of low metallicities in dwarf galaxies.

Dynamics of interacting bosons in a double-well potential

We present effects of an external driving on the tunneling dynamics of interacting bosons confined in a double-well potential. At large values of a periodic driving potential, the dynamics become chaotic, with a distinct difference between tuning of the amplitude or the phase of the driving term with regard to the route leading to chaos. For example, we find that a controlled increase in the amplitude of the driving term with a fixed phase leads to quasiperiodic route to chaos. While tuning of the frequency with a fixed (large) amplitude leads to a crisis-induced intermittency route to a chaotic dynamics, where the system intermittently visits different attractors in the phase space. Surprisingly, a chirp frequency superposed on a harmonic signal suppresses the chaotic motion, thereby yielding an orderly dynamics, pretty similar to a (damped) Rabi oscillation.

First-principles computational design of unknown flat arsenene epitaxially grown on copper substrate

Two-dimensional materials play essential roles in utilizing surface reactions, such as catalysts, adsorption and separation of chemicals. Especially, group-V mono-elemental materials are highlighted for transistors, optoelectronic devices, and mechanical sensors. Here, we identify unknown honeycomb-type arsenene epitaxially grown on copper substrate using first-principles density functional theory calculations. Key materials properties of lattice mismatch, thermodynamic stability, and surface transport properties are evaluated to verify the feasibility of the structural formation. Furthermore, ab-initio molecular dynamic simulations and scanning tunneling microscopy simulations clearly describe the mechanism of the initial nucleation and growth process. Electronic structure-level calculations characterize a strong covalency between each As atom pair. Our approach combining electronic structure calculations and thermodynamic/kinetic property predictions can be useful for quick screening and plausible design of new low-dimensional materials, which can efficiently functionalize emerging surface systems.

UAV aerodynamic design involving genetic algorithm and artificial neural network for wing preliminary computation

In this paper, the aerodynamic design procedure of a mini unmanned aerial vehicle, intended to perform aerial reconnaissance at low altitude and low Reynolds number, was summarized. Design process was divided into two major parts: conceptual design phase and preliminary design phase. During the conceptual design, classical procedures and data from similar unmanned aerial vehicles already designed were employed to define the requirements related to unmanned aerial vehicle design. The preliminary design was performed using panel method where the emphasis was given on the design of the UAV wing, fuselage design and empennage. The wing planform parameters were determined through an aerodynamic optimization process using both genetic algorithms and artificial neural networks. Finally an aerodynamic analysis using panel method, Computational Fluid Dynamic simulations and wind tunnel testing was carried out. Unmanned aerial vehicle full configuration design process was consistent, where a comparison between the final obtained results was carried out and showed an agreement in terms of lift, drag and pitch moment coefficients.

Experimentally validated CFD simulations predicting wind effects on photovoltaic modules mounted on inclined surfaces

Computational Fluid Dynamics (CFD) and wind tunnel experiments were used to study wind flow over PV modules attached to inclined surfaces. Wind velocities were investigated at various positions on a test module, for five wind speeds varying from 1 to 5 m s−1. After validation the CFD model was used to study the effects air gaps and wall cavities under the module have on the airflow over the module. Data were measured for two air gaps, 3.5 cm and 5.5 cm thick, and for three cavity depths ranging from 0 cm to 9 cm. The 3.5 cm air gap resulted in lower near-surface wind speeds over the PV module. This will result in less wind-generated cooling of the module, and consequently, in a lower electrical performance. The wall cavities did not affect the magnitude of the wind speed over the module but generated an increased deflection of the wind towards the lateral sides of the module. They also created clockwise and anti-clockwise eddies next to the PV setup and in the cavity itself. The study shows that in CFD simulations for PV applications, even small irregularities in the PV setup should be included in the model to predict reliable results.

Relevance of the Resonance Junctions on the Arnold Web to Dynamical Tunneling and Eigenstate Delocalization.

We study the competition and correspondence between the classical and quantum routes to intramolecular vibrational energy redistribution (IVR) in a three degrees of freedom model effective Hamiltonian. Specifically, we focus on the classical and the quantum dynamics near the resonance junctions on the Arnold web that are formed by an intersection of independent resonances. The regime of interest models the IVR dynamics from highly excited initial states near dissociation thresholds of molecular systems wherein both classical and purely quantum, involving dynamical tunneling, routes to IVR coexist. In the vicinity of a resonance junction, classical chaos is inevitably present, and hence one expects the quantum IVR pathways to have a strong classical component as well. We show that with increasing resonant coupling strengths the classical component of IVR leads to a transition from coherent dynamical tunneling to incoherent dynamical tunneling. Furthermore, we establish that the quantum IVR dynamics can be predicted based on the structures on the classical Arnold web. In addition, we investigate the nature of the highly excited eigenstates to identify the quantum signatures of the multiplicity-2 junctions. For the parameter regimes studies herein, by projecting the eigenstates onto the Arnold web, we find that eigenstates in the vicinity of the junctions are primarily delocalized due to dynamical tunneling.

Exploring quantum chaos with a single nuclear spin

Most classical dynamical systems are chaotic. The trajectories of two identical systems prepared in infinitesimally different initial conditions diverge exponentially with time. Quantum systems, instead, exhibit quasi-periodicity due to their discrete spectrum. Nonetheless, the dynamics of quantum systems whose classical counterparts are chaotic are expected to show some features that resemble chaotic motion. Among the many controversial aspects of the quantum-classical boundary, the emergence of chaos remains among the least experimentally verified. Time-resolved observations of quantum chaotic dynamics are particularly rare, and as yet unachieved in a single particle, where the subtle interplay between chaos and quantum measurement could be explored at its deepest levels. We present here a realistic proposal to construct a chaotic driven top from the nuclear spin of a single donor atom in silicon, in the presence of a nuclear quadrupole interaction. This system is exquisitely measurable and controllable, and possesses extremely long intrinsic quantum coherence times, allowing for the observation of subtle dynamical behavior over extended periods. We show that signatures of chaos are expected to arise for experimentally realizable parameters of the system, allowing the study of the relation between quantum decoherence and classical chaos, and the observation of dynamical tunneling.

Coherent extreme-ultraviolet emission generated through frustrated tunnelling ionization

Coherent extreme-ultraviolet emission can be obtained through high-harmonic generation and multiphoton excitation from atoms exposed to a strong laser field. We report the generation of a new kind of coherent extreme-ultraviolet emission from He atoms excited by intense few-cycle laser pulses. An atom can be excited after tunnelling in a strong laser field, in the process known as frustrated tunnelling ionization (FTI). We find that excitation through FTI leads to coherent extreme-ultraviolet emission, and its intensity strongly depends on the ellipticity and carrier-envelope phase of the laser pulses. Additionally, the propagation direction of the emission can be coherently controlled by employing the attosecond lighthouse technique. This coherent control of tunnelling and recombination dynamics, which has provided the fundamental basis of attosecond physics, promises the utilization of FTI emission as a coherent light source and offers new opportunities in ultrafast spectroscopy. Coherent extreme-ultraviolet emission through frustrated tunnelling ionization is observed from He atoms excited by intense few-cycle infrared laser pulses. Its intensity depends on the ellipticity and the carrier-envelope phase of the infrared laser.

Tunneling dynamics of bosons in the diamond lattice chain**Project supported by the National Natural Science Foundation of China (Grant Nos. 11764039, 11475027, 11865014, 11865014, 11274255, and 11305132), the Natural Science Foundation of Gansu Province, China (Grant No. 17JR5RA076), and the Scientific Research Project of the Higher Education of Gansu Province, China (Grant No. 2016A-005).

We analyze the effect of tilting and artificial magnetic flux, on the energy bands structure for the system and the corresponding tunneling dynamics for bosons with various initial configurations in the diamond lattice chain, where intriguing and significant phenomena occur, including Landau–Zener tunneling, Bloch oscillations, and localization phenomenon. Both vertical tilting and artificial magnetic flux may alter the structure of energy levels (dispersion structure or flat band), and enforce the occurrence of Landau–Zener tunneling, which scans the whole of the Bloch bands. We find that, transitions among Landau–Zener tunneling, Bloch oscillations, and localization phenomenon, are not only closely related to the energy bands structure, but also depends on the initial configuration of bosons in the diamond lattice chain. As a consequence, Landau–Zener tunneling, Bloch oscillations, and localization phenonmenon of bosons always counteract and are complementary with each other in the diamond lattice chain.

The digging dynamics of ant tunnels: movement, encounters, and nest space

Underground ant nests are constructed by decentralised self-organisation wherein the ants respond to local stimuli and produce coordinated structures through globally regulated behaviours. One such regulation is the reduction in digging effort that occurs when available nest space has reached an adequate size. Tunnels have a distinct configuration relative to other nest elements and the processes regulating their excavation are poorly understood. We examined the relationship between digging effort and tunnel space by presenting groups of 10 Acromyrmex lundi workers with either short or long tunnel spaces and demonstrated that they will dig significantly less over time in a tunnel that is already long compared to one that is short. Additionally, we provided the same treatment to groups of 100 workers and found no significant effect of length, suggesting that group size has an important impact on tunnel excavation dynamics. Automated tracking was then used to examine tunnel digging in greater detail. Groups of 10 Atta colombica ants were tracked while excavating sand in a tunnel apparatus. There was a significant correlation between mean walking speed and excavation rate. Additionally, the ants would maintain a consistent level of proximity with each other over time. This suggests that as tunnel space expands, several factors combine to lower the chance of ants encountering the tunnel digging face and taking up excavation.

For high-precision bosonic Josephson junctions, many-body effects matter

Typical treatments of superconducting or superfluid Josephson junctions rely on mean-field or two-mode models; we explore many-body dynamics of an isolated, ultracold, Bose-gas long Josephson junction using time-evolving block decimation simulations. We demonstrate that with increasing repulsive interaction strength, localized dynamics emerge that influence macroscopic condensate behavior and can lead to the formation of solitons that directly oppose the symmetry of the junction. Initial state population and phase yield insight into dynamic tunneling regimes of a quasi one-dimensional double well potential, from Josephson oscillations to macroscopic-self-trapping. Population imbalance simulations reveal substantial deviation of many-body dynamics from mean-field Gross–Pitaevskii predictions, particularly as the barrier height and interaction strength increase. In addition, the sudden approximation supports localized particle–hole formation after a diabatic quench, and correlation measures unveil a new dynamic regime: the Fock flashlight.

Tailoring Single-Cycle Near Field in a Tunnel Junction with Carrier-Envelope Phase-Controlled Terahertz Electric Fields.

Light-field-driven processes occurring under conditions far beyond the diffraction limit of the light can be manipulated by harnessing spatiotemporally tunable near fields. A tailor-made carrier envelope phase in a tunnel junction formed between nanogap electrodes allows precisely controlled manipulation of these processes. In particular, the characterization and active control of near fields in a tunnel junction are essential for advancing elaborate manipulation of light-field-driven processes at the atomic-scale. Here, we demonstrate that desirable phase-controlled near fields can be produced in a tunnel junction via terahertz scanning tunneling microscopy (THz-STM) with a phase shifter. Measurements of the phase-resolved subcycle electron tunneling dynamics revealed an unexpected large carrier-envelope phase shift between far-field and near-field single-cycle THz waveforms. The phase shift stems from the wavelength-scale feature of the tip-sample configuration. By using a dual-phase double-pulse scheme, the electron tunneling was coherently manipulated over the femtosecond time scale. Our new prescription-in situ tailoring of single-cycle THz near fields in a tunnel junction-will offer unprecedented control of electrons for ultrafast atomic-scale electronics and metrology.

RESEARCH ON DYNAMIC TEST TECHNOLOGY FOR WIND TURBINE BLADE AIRFOIL

The dynamic oscillation process of wind turbine blades is usually accompanied by pitching and yaw. Due to the unclear understanding of many dynamic problems previously, a safer design is adopted at the expense of increasing the weight of the blade structure in engineering, usually neglecting the influence of the yaw oscillation. The design of large wind turbines has put forward higher requirements for obtaining more comprehensive and accurate dynamic loads of airfoils. It is of great significance to study the influence of yaw oscillation on the dynamic aerodynamic characteristics of airfoil. In view of this, the dynamic wind tunnel test on yaw oscillation of airfoil is carried out in this paper for the first time. The “electronic cam” technology is used instead of the mechanical cam to realize the stepless adjustment of oscillation frequency and oscillation angle. Based on the designed electronic external trigger device, the real-time measurement of the dynamic flow field is realized. Meanwhile, the synchronous acquisition of wind tunnel flow, model angular displacement and dynamic pressure data is realized. Furthermore, the static pressure measurement, pitching / yaw dynamic pressure measurement, PIV and fluorescent wire test are carried out respectively. The accuracy of the test results is high, and the regular pattern is reasonable. Besides, the influence mechanism of wall interference in dynamic test is analyzed. Research shows that: there is also obvious hysteresis effect on the dynamic aerodynamic parameters of yaw oscillation airfoil with the changing of the angle of attack. And with the increase of oscillation frequency, the aerodynamic hysteresis characteristics of the airfoil under pitching and yaw oscillation are all enhanced. The dynamic stall vortex at the positive stroke is delayed due to the pitching oscillation. The pressure distribution of the airfoil is greatly influenced by the strong three-dimensional effect at the intersection of the wind tunnel wall and the model tip. Overall, the dynamic test technique of yaw oscillation established in this paper can provide technical support for the study of the dynamic swept effect of the wind turbines.

Tunneling criteria and a nonadiabatic term for strong-field ionization

We investigate tunneling ionization of a model helium atom in a strong circularly polarized short laser pulse using the classical backpropagation method and compare ten different tunneling criteria on the same footing, aiming for a consistent classical picture of the tunneling dynamics. These tunneling criteria are categorized into velocity-based, position-based, and energy-based criteria according to different notions of a tunnel exit. We find that velocity-based criteria give consistent tunneling exit characteristics with nonadiabatic effects fully included. Other criteria are either inconsistent or only able to include nonadiabatic effects partially. Furthermore, we construct a simple tunneling rate formula, identify a term in the rate responsible for the nonadiabatic effects, and demonstrate the importance of this term.

Sampling-Based Motion Planning for Tracking Evolution of Dynamic Tunnels in Molecular Dynamics Simulations

Proteins are involved in many biochemical processes. The behavior of proteins is highly influenced by the presence of internal void space, in literature denoted as tunnels or cavities. Tunnels are paths leading from an inner protein active site to its surface. The knowledge about tunnels and their evolution over time, captured in molecular dynamics simulations, provides an insight into important protein properties (e.g., their stability or activity). For each individual snapshot of molecular dynamics, tunnels can be detected using Voronoi diagrams and then aggregated over time to trace their behavior. However, this approach is suitable only when a given tunnel is detected in all snapshots of molecular dynamics. This is often not the case of traditionally used approaches to tunnel computation. When a tunnel becomes too narrow in a particular snapshot, the existing approaches cannot detect this case and the tunnel completely disappears from the results. On the other hand, this situation can be quite common as tunnels move, disappear and appear again, split, or merge. Therefore, in this paper we propose a method which enables to trace also tunnels in those missing snapshots. We call them dynamic tunnels and we use the sampling-based motion planning to compute them. The Rapidly Exploring Random Tree (RRT) algorithm is used to explore the void space in each frame of the protein dynamics. The void space is represented by a tree structure that is transferred to the next frame of the dynamics and updated to remove collisions and to cover newly emerged free regions of the void space. If the void space reaches the surface of the protein, a dynamic tunnel is reconstructed by tracking back in the tree towards a desired place (i.e., the active site). To efficiently sample the narrow void space inside proteins, a Voronoi diagram of the static protein frames is used. The results of the proposed method are demonstrated on an exemplary dataset obtained from the domain experts and the results are compared with the classic aggregation-based tunnel detection performed using the state-of-the-art CAVER 3.0 tool.

Symmetry breaking and tunneling dynamics of a dipolar Bose–Einstein condensate in a double-well potential

We investigate the properties of a three-dimensional (3D) dipolar Bose–Einstein condensate (BEC) in a double-well potential (DWP). Symmetry breaking and tunneling dynamics phenomena are demonstrated for 164Dy atoms in the 3D DWP using an effective two-mode model. The results show that the symmetry properties of the dynamics are affected markedly by the long-range nature and anisotropy of the dipolar interaction and the isotropic contact interaction.

Testing of a Hinged Wingtip Device for Gust Loads Alleviation

Recent aircraft designs have considered higher-aspect-ratio wings to reduce induced drag for improved fuel efficiency; however, to remain compliant with airport gate requirements, folding wingtips have been introduced as a solution to the increased wingspan. Recent numerical studies suggest that a folding wingtip solution may be incorporated with spring devices to provide an additional gust loads alleviation ability in flight as well. In this work, a series of low-speed steady and dynamic wind tunnel tests was conducted using a prototype of such a concept. It was found that a folding wingtip with a nonzero relative angle of the folding hinge axis to the streamwise direction could provide gust loads alleviation. The level of load alleviation varied with hinge spring stiffness and lifting condition, with the best performance achieving a 56% reduction in peak loading.