Trap Geometry Research Articles

Different atom trapping geometries with time averaged adiabatic potentials

In this article, we have theoretically studied the time averaged adiabatic potential (TAAP) scheme for realizing different atom trapping geometries. It is shown that by varying time orbiting potential (TOP) fields and radio frequency (rf) fields parameters, controlled manipulation of trapping potentials, and conversion from one trapping geometry to another, is possible. The proposed trapping geometries can be useful for studying various atom-optic phenomena such as Bose-Einstein condensation (BEC) in low dimensions, super-fluidity, tunnelling, atom interferometry, etc.

Electric trapping and circuit cooling of charged nanorotors

The motion of charged particles can be interfaced with electric circuitry via the current induced in nearby pick-up electrodes. Here we show how the rotational and translational dynamics of levitated objects with arbitrary charge distributions can be coupled to a circuit and how the latter acts back on the particle motion. The ensuing cooling rates in series and parallel RLC circuits are determined, demonstrating that quadrupole ion traps are well suited for implementing all-electric cooling. We derive the effective macromotion potential for general trap geometries and illustrate how consecutive rotational and translational resistive cooling of a microscale particle can be achieved in linear Paul traps.

The impact of multiple concurrent factors on the length of the ultrasound pulmonary vertical artifacts as illustrated through the experimental and numerical analysis of simple models.

Nowadays, the diagnostic value of the artefactual information provided by lung ultrasound images is widely recognized by physicians. By carefully observing each individual artifact, an expert physician can derive important information on the distribution of the aerated spaces at the pleural level and, consequently, on the nature of the pulmonary disease. In this paper, a specific visual characteristic of the vertical artifacts (their length) is addressed. The impact of the acoustic properties of the interstitial medium, of the imaging parameters, and of the trap geometry on the length of the vertical artifacts is illustrated through experimental results and through the theoretical analysis of a simple model.

Ramsey Imaging of Optical Traps

Mapping the potential landscape with high spatial resolution is crucial for quantum technologies based on ultracold atoms. Yet, imaging optical dipole traps is challenging because purely optical methods, commonly used to profile laser beams in free space, are not applicable in vacuum. In this work, we demonstrate precise in-situ imaging of optical dipole traps by probing a hyperfine transition with Ramsey interferometry. Thereby, we obtain an absolute map of the potential landscape with micrometer resolution and shot-noise-limited spectral precision. The idea of the technique is to control the polarization ellipticity of the trap laser beam to induce a differential light shift proportional to the trap potential. By studying the response to polarization ellipticity, we uncover a small but significant nonlinearity in addition to a dominant linear behavior, which is explained by the geometric distribution of the atomic ensemble. Our technique for imaging of optical traps can find wide application in quantum technologies based on ultracold atoms, as it applies to multiple atomic species and is not limited to a particular wavelength or trap geometry.

Pattern formation in quantum ferrofluids: From supersolids to superglasses

Pattern formation is a ubiquitous phenomenon observed in nonlinear and out-of-equilibrium systems. In equilibrium, quantum ferrofluids formed from ultracold atoms were recently shown to spontaneously develop coherent density patterns, manifesting a supersolid. We theoretically investigate the phase diagram of such quantum ferrofluids in oblate trap geometries and find an even wider range of exotic states of matter. Two-dimensional supersolid crystals formed from individual ferrofluid quantum droplets dominate the phase diagram at low densities. For higher densities we find honeycomb and labyrinthine states, as well as a pumpkin phase. We discuss scaling relations which allow us to find these phases for a wide variety of trap geometries, interaction strengths, and atom numbers. Our study illuminates the origin of the various possible patterns of quantum ferrofluids and shows that their occurrence is generic of strongly dipolar interacting systems stabilized by beyond mean-field effects.

Characterization of the energy level-structure of a trapped dipolar Bose gas via mean-field parametric resonances

Analyzing the energy levels of a trapped Bose–Einstein condensate (BEC) can be difficult when dipole-dipole interactions (DDIs) are present. To address this issue, this study focuses on the parametric resonances (PRs) in the mean-field dynamics of a one-dimensional dipolar BEC (DBEC) over widely varying trapping geometries, with the primary objective of characterizing the energy levels of this system via analytical methods. This is achieved by matching the PR energies to the energy levels of the confining trap using perturbative methods. Further, this research reveals the role of the interplay between DDIs and the trapping geometry in defining the energies and amplitudes of the PRs. The PRs are induced by a negative Gaussian potential with a depth that oscillates with respect to time; DDIs also play a role in this induction. The dynamics of this system are modeled using the time-dependent Gross–Pitaevskii equation (TDGPE), which is numerically solved via the Crank–Nicolson method. The PRs are discussed based on analytical methods. First, we show that PRs similar to the ones obtained from the TDGPE can be reproduced via the Lagrangian variational method. Second, the energies at which the PRs occur are closely matched with the energy levels of the corresponding trap, calculated using the time-independent perturbation theory. Third, the most probable transitions between the trap energy levels yielding PRs are determined based on the time-dependent perturbation theory. The primary contribution of this research is that the energy levels of a DBEC within a complex trapping potential could be characterized.

Effect of geometry on dielectrophoretic trap stiffness in microparticle trapping.

Dielectrophoresis, an electrokinetic technique, can be used for contactless manipulation of micro- and nano-size particles suspended in a fluid. We present a 3-D microfluidic DEP device with an orthogonal electrode configuration that uses negative dielectrophoresis to trap spherical polystyrene micro-particles. Traps with three different basic geometric shapes, i.e. triangular, square, and circular, and a fixed trap area of around 900 μm2 were investigated to determine the effect of trap shape on dynamics and strength of particle trapping. Effects of trap geometry were quantitatively investigated by means of trap stiffness, with applied electric potentials from 6 VP-P to 10 VP-P at 1MHz. Analyzing the trap stiffness with a trapped 4.42μm spherical particle showed that the triangular trap is the strongest, while the square shape trap is the weakest. The trap stiffness grew more than eight times in triangular traps and six times in both square and circular traps when the potential of the applied electric field was increased from 6 VP-P to 10 VP-P at 1MHz. With the maximum applied potential, i.e. 10 VP-P at 1MHz, the stiffness of the triangular trap was 60% and 26% stronger than the square and circular trap, respectively. A finite element model of the microfluidic DEP device was developed to numerically compute the DEP force for these trap shapes. The findings from the numerical computation demonstrate good agreement with the experimental analysis. The analysis of three different trap shapes provides important insights to predict trapping location, strength of the trapping zone, and optimized geometry for high throughput particle trapping.

Large-area Rb87 Bose-Einstein condensate in a clipped-Gaussian optical dipole trap

We demonstrate a production of large-area $^{87}$Rb Bose-Einstein condensates (BECs) using a non-Gaussian optical dipole trap (ODT). The ODT is formed by focusing a symmetrically truncated Gaussian laser beam and it is shown that the beam clipping causes the trap geometry elongated and flattened along the beam axis direction. In the clipped-Gaussian ODT, an elongated, highly oblate BEC of $^{87}$Rb is generated with length and width of approximately $470~\mu\textrm{m}$ and $130~\mu\textrm{m}$, respectively, where the condensate healing length is estimated to be $\xi\approx 0.25~\mu\textrm{m}$ at the trap center. The ODT is characterized to have a quartic trapping potential along the beam axis and the atom density of the condensate is uniform within 10% over $1000\xi$ in the central region. Finally, we discuss the prospect of conducting vortex shedding experiments using the elongated condensate.

Relaxation in an extended bosonic Josephson junction

We present a detailed analysis of the relaxation dynamics in an extended bosonic Josephson junction. We show that stochastic classical field simulations using Gross-Pitaevskii equations in three spatial dimensions reproduce the main experimental findings of M. Pigneur et al., Phys. Rev. Lett. 120, 173601 (2018). We give an analytic solution describing the short time evolution through multimode dephasing. For longer times, the observed relaxation to a phase locked state is caused by nonlinear dynamics beyond the sine-Gordon model, induced by the longitudinal confinement potential and persisting even at zero temperature. Finally, we analyze different experimentally relevant trapping geometries to mitigate these effects. Our results provide the basis for future experimental implementations aiming to study nonlinear and quantum effects of the relaxation in extended bosonic Josephson junctions.

Transition from an atomic to a molecular Bose-Einstein condensate.

Molecular quantum gases (that is, ultracold and dense molecular gases) have many potential applications, including quantum control of chemical reactions, precision measurements, quantum simulation and quantum information processing1-3. For molecules, to reach the quantum regime usually requires efficient cooling at high densities, which is frequently hindered by fast inelastic collisions that heat and deplete the population of molecules4,5. Here we report the preparation of two-dimensional Bose-Einstein condensates (BECs) of spinning molecules by inducing pairing interactions in an atomic condensate near a g-wave Feshbach resonance6. The trap geometry and the low temperature of the molecules help to reduce inelastic loss, ensuring thermal equilibrium. From the equation-of-state measurement, we determine the molecular scattering length to be + 220(±30)Bohr radii (95% confidence interval). We also investigate the unpairing dynamics in the strong coupling regime and find that near the Feshbach resonance the dynamical timescale is consistent with the unitarity limit. Our work demonstrates the long-sought transition between atomic and molecular condensates, the bosonic analogue of the crossover from a BEC to a Bardeen-Cooper-Schrieffer (BCS) superfluid in a Fermi gas7-9. In addition, our experiment may shed light on condensed pairs with orbital angular momentum, where a novel anisotropic superfluid with non-zero surface current is predicted10,11, such as the A phase of 3He.

Three-dimensional random walk models of individual animal movement and their application to trap counts modelling

Random walks (RWs) have proved to be a powerful modelling tool in ecology, particularly in the study of animal movement. An application of RW concerns trapping which is the predominant sampling method to date in insect ecology and agricultural pest management. A lot of research effort has been directed towards modelling ground-dwelling insects by simulating their movement in 2D, and computing pitfall trap counts, but comparatively very little for flying insects with 3D elevated traps. We introduce the mathematics behind 3D RWs and present key metrics such as the mean squared displacement (MSD) and path sinuosity, which are already well known in 2D. We develop the mathematical theory behind the 3D correlated random walk (CRW) which involves short-term directional persistence and the 3D Biased random walk (BRW) which introduces a long-term directional bias in the movement so that there is an overall preferred movement direction. In this study, we focus on the geometrical aspects of the 3D trap and thus consider three types of shape; a spheroidal trap, a cylindrical trap and a rectangular cuboidal trap. By simulating movement in 3D space, we investigated the effect of 3D trap shapes and sizes and of movement diffusion on trapping efficiency. We found that there is a non-linear dependence of trap counts on the trap surface area or volume, but the effect of volume appeared to be a simple consequence of changes in area. Nevertheless, there is a slight but clear hierarchy of trap shapes in terms of capture efficiency, with the spheroidal trap retaining more counts than a cylinder, followed by the cuboidal type for a given area. We also showed that there is no effect of short-term persistence when diffusion is kept constant, but trap counts significantly decrease with increasing diffusion. Our results provide a better understanding of the interplay between the movement pattern, trap geometry and impacts on trapping efficiency, which leads to improved trap count interpretations, and more broadly, has implications for spatial ecology and population dynamics.

Arbitrary-angle rotation of the polarization of a dipolar Bose-Einstein condensate

We have employed the theory of harmonically trapped dipolar Bose-Einstein condensates to examine the influence of a uniform magnetic field that rotates at an arbitrary angle to its own orientation. This is achieved by semi-analytically solving the dipolar superfluid hydrodynamics of this system within the Thomas-Fermi approximation and by allowing the body frame of the condensate's density profile to be tilted with respect to the symmetry axes of the nonrotating harmonic trap. This additional degree of freedom manifests itself in the presence of previously unknown stationary solution branches for any given dipole tilt angle. We also find that the tilt angle of the stationary state's body frame with respect to the rotation axis is a nontrivial function of the trapping geometry, rotation frequency, and dipole tilt angle. For rotation frequencies of at least an order of magnitude higher than the in-plane trapping frequency, the stationary state density profile is almost perfectly equivalent to the profile expected in a time-averaged dipolar potential that effectively vanishes when the dipoles are tilted along the ``magic angle'' 54.7 deg. However, by linearizing the fully time-dependent superfluid hydrodynamics about these stationary states, we find that they are dynamically unstable against the formation of collective modes, which we expect would result in turbulent decay.

Spectral properties of a three-body atom-ion hybrid system

We consider a hybrid atom-ion system consisting of a pair of bosons interacting with a single ion in a quasi-one-dimensional trapping geometry. Building upon a model potential for the atom-ion interaction developed in earlier theoretical works, we investigate the behaviour of the low-energy eigenstates for varying contact interaction strength $g$ among the atoms. In particular, we contrast the two cases of a static and a mobile ion. Our study is carried out by means of the Multi-Layer Multi-Configuration Time-Dependent Hartree method for Bosons, a numerically-exact $\textit{ab initio}$ method for the efficient simulation of entangled mixtures. We find that repulsive atom interactions induce locally-distinct modifications of the atomic probability distribution unique to each eigenstate. Whilst the atoms on average separate from each other with increasing $g$, they do not necessarily separate from the ion. The mobility of the ion leads in general to greater separations among the atoms as well as between the atoms and the ion. Notably, we observe an exchange between the kinetic energy of the atoms and the atom-ion interaction energy for all eigenstates, which is both interaction- and mobility-induced. For the ground state, we provide an intuitive description by constructing an effective Hamiltonian for each species, which aptly captures the response of the atoms to the ion's mobility. Furthermore, the effective picture predicts enhanced localisation of the ion, in agreement with our results from exact numerical simulations.

Effect of trap symmetry and atom-atom interactions on a trapped-atom interferometer with internal state labeling

In this paper, we study the dynamics of a trapped atom interferometer with internal state labelling in the presence of interactions. We consider two situations: an atomic clock in which the internal states remain superposed, and an inertial sensor configuration in which they are separated. From the average spin evolution, we deduce the fringe contrast and the phase-shift. In the clock configuration, we recover the well-known identical spin rotation effect (ISRE) which can significantly increase the spin coherence time. We also find that the magnitude of the effect depends on the trap geometry in a way that is consistent with our recent experimental results in a clock configuration [M. Dupont-Nivet, and al., New J. Phys., 20, 043051 (2018)], where ISRE was not observed. In the case of an inertial sensor, we show that despite the spatial separation it is still possible to increase the coherence time by using mean field interactions to counteract asymmetries of the trapping potential.

Quantitative analysis of the three-dimensional trap stiffness of a dielectrophoretic corral trap.

Dielectrophoresis is a robust approach for the manipulation and separation of (bio)particles using microfluidic platforms. We developed a dielectrophoretic corral trap in a microfluidic device that utilizes negative dielectrophoresis to capture single spherical polystyrene particles. Circular-shaped micron-size traps were employed inside the device and the three-dimensional trap stiffness (restoring trapping force from equilibrium trapping location) was analyzed using 4.42μm particles and 1MHz of an alternating electric field from 6 VP-P to 10 VP-P . The trap stiffness increased exponentially in the x- and y-direction, and linearly in the z-direction. Image analysis of the trapped particle movements revealed that the trap stiffness is increased 608.4, 539.3, and 79.7% by increasing the voltage from 6 VP-P to 10 VP-P in the x-, y-, and z-direction, respectively. The trap stiffness calculated from a finite element simulation of the device confirmed the experimental results. This analysis provides important insights to predict the trapping location, strength of the trapping, and optimum geometry for single particle trapping and its applications such as single-molecule analysis and drug discovery.

Hydrocarbon accumulation in basins with multiple phases of extension and inversion: examples from the Western Desert (Egypt) and the western Black Sea

Abstract. Folds associated with inverted extensional faults are important exploration targets in many basins across our planet. A common cause for failure to trap hydrocarbons in inversion structures is crestal breaching or erosion of top seal. The likelihood of failure increases as the intensity of inversion grows. Inversion also decreases the amount of overburden, which can adversely affect maturation of source rocks within the underlying syn-extensional stratigraphic section. However, many rift basins are multi-phase in origin, and in some cases the various syn-rift and post-rift events are separated by multiple phases of shortening. When an inversion event is followed by a later phase of extension and subsidence, new top seals can be deposited and hydrocarbon maturation enhanced or reinitiated. These more complex rift histories can result in intra-basinal folds that have higher chances of success than single-phase inversion-related targets. In other basins, repeated inversion events can occur without significant intervening extension. This can also produce more complicated hydrocarbon maturation histories and trap geometries. Multiple phases of rifting and inversion affected numerous basins in North Africa and the Black Sea region and produced some structures that are now prolific hydrocarbon producing fields and others that failed. Understanding a basin's sequence of extensional and contractional events and the resulting complex interactions is essential to formulating successful exploration strategies in these settings.

EVALUATION OF CDC LIGHT TRAP, BG SENTINEL TRAP, AND MMX TRAP FOR THE COLLECTION OF SALT MARSH MOSQUITOES IN ANASTASIA STATE PARK, SAINT AUGUSTINE, FLORIDA

Salt marsh mosquitoes are major nuisance pests during the periods of high mosquito activity, especially after major storm events. In 2016-2017, Saint John’s County, Florida, USA was struck by two major hurricanes that resulted in multiple outbreaks of salt marsh mosquito populations. To optimize the surveillance of two salt marsh mosquitoes, (Aedes taeniorhynchus and Ae. sollicitans, three types of traps (the Centers for Disease Control (CDC) Light trap, Biogents Sentinel (BG) trap and Counter Flow Geometry Model (MMX) trap were tested for their capacity to capture the highest numbers of high quality live specimens for laboratory bioassays. Each trap type was tested in Anastasia State Park, located along a major salt marsh area in Saint John’s County. Although the MMX trap captured most of the salt marsh mosquitoes collected, the numbers of mosquitoes captured was not statistically significant compared to the other trap types. However, there was a significant difference in the numbers between Ae. taeniorhynchus and Ae. sollicitans in the MMX traps. The MMX trap is preferred for capturing salt marsh mosquitoes that are in high quality for the CDC bottle bioassays.

Assessing Hydrocarbon Prospectivity in the Lower Cretaceous Syn-rift Half-Grabens in the Offshore Benin Basin

3D seismic data acquired in the Nigerian sector of the offshore Benin Basin reveal two sets of half-graben mini-basins and fault framework trending ENE-WSW and another trending NW-SE and orthogonal to the former, separated by basement horst. It is also seen that the basement, base Albian unconformity and down to basement faults all play key roles on hydrocarbon trapping geometries. Hydrocarbon traps consists of a combined structural and stratigraphic configuration. The structural element is created by the extensional half-graben bounding faults, while the unconformity at the base of the Albian and the basement constitutes the stratigraphic element. Impedance model shows several potention reservoir/seal pairs while the top seal is a regionally extensive shale at the base of the Albian. Isopach map of the syn-rift basins suggest sedimentary fill sufficiently thick for source rock maturation and hydrocarbon generation. Hydrocarbon migration is speculated to be along regional basement faults and sediment-basement interface. The Ogo-2 well discovery has perhaps opened up a completely new syn-rift play in the Nigerian sector of the basin with significant opportunities yet to be tested along the West African Transform Margin trend.

Breakup of rotating asymmetric quartic-quadratic trapped condensates

The threshold conditions for a rotating pancake-like asymmetric quartic-quadratic confined condensate to break in two localized fragments, as well as to produce giant vortex at the center within the vortex-pattern distributions, are investigated within the Thomas-Fermi (TF) approximation and exact numerical solution of the corresponding Gross-Pitaevskii (GP) formalism. By comparing the TF predictions with exact GP solutions, in our investigation with two different quartic-quadratic trap geometries, of particular relevance is to observe that the TF approach is not only very useful to display the averaged density distribution, but also quite realistic in establishing the critical rotational conditions for the breakup occurrence and possible giant-vortex formation. It provides almost exact results to define the contour of the condensate distribution, even for high rotating system, after the system split in two (still confined) clouds. The applicability of the Feynman rule to the vortex distribution (full-numerical GP solutions) is also being confirmed for these non-homogeneous asymmetric trap configurations. This study is expected to be relevant for manipulating the rotation and trap parameters in addition to Feshbach resonance techniques. It can also be helpful to define initial conditions for any further studies on dynamical evolution of vortex pattern distributions.

Opto-electrical characterization of quaternary sputtered copper indium gallium selenide nanorods via glancing angle deposition

Nanorod arrays have become an attractive alternative to their thin film and bulk counterparts in photovoltaic and photoconductivity research. This is mainly attributed to their superior optical and electrical properties. Light trapping and unique bandgap geometries in vertically aligned nanostructures result in high optical absorption and provide enhanced carrier collection by utilizing a fully depleted p-n junction between the anode and cathode via an isolated “capping” construction. The combination of these two features leads to the development of high efficiency nanostructured devices that can be utilized in solar cells and photodetectors. Optical absorption properties, geometry, and opto-electrical properties of nanorod arrays of CuInxGa(1−x)Se2 (CIGS), a p-type semiconductor with a wide bandgap ranging from 1.0 to 1.7 eV, are compared to their thin film counterparts. Utilizing a radio frequency sputtering system, a quaternary target, and glancing angle deposition technique, both isolated vertical arrays of CIGS nanorods and “core-shell” devices were fabricated, while conventional film devices were fabricated by normal incidence deposition. Scanning electron microscopy images indicated a successful growth of CIGS nanorods. Optical absorption and opto-electrical performance were found to be strongly improved by the presence of the isolated nanorod structures through spectroscopic reflectometry and responsivity testing under a solar simulator.