Realistic Trap Research Articles

Manipulating phonons of a trapped-ion system using optical tweezers

We propose an experimental architecture where an array of optical tweezers affords site-dependent control over the confining potential of a conventional radio-frequency ion trap. The site-dependent control enables programmable manipulation of phonon modes of ions, with many potential applications in quantum information processing (QIP) and thermodynamics. We describe protocols for programming the array of optical tweezers to attain a set of target phonon modes with high accuracy. We propose applications of such controls in simulating quantum thermodynamics of a particle of programmable effective mass via Jarzynski's equality and improving the efficiency of sympathetic cooling and quantum logic gates in a multispecies ion system of disparate masses. We discuss the required optical parameters in a realistic ion trap system and potential adverse effects of optical tweezers in QIP. Our scheme extends the utility of trapped ions as a platform for quantum computation and simulation.

An analytical approach to symmetry breaking in multipole RF-traps

Radio-frequency (RF) linear multipole traps have been shown to be very sensitive to mis-positioning of their electrodes, which results in a symmetry breaking and leads to extra local minima in the trapping potential as shown in Pedregosa-Gutierrez et al (2018 J. Mod. Opt. 65 529) disturbing the operation of the trap. In this work, we analytically describe the RF-potential of a realistic octupole trap by including lower order terms to the well-established equation for a perfectly symmetric octupole trap. We describe the geometry by a combination of identified defects, characterized by simple analytical expressions. A complete equation is proposed for a trap with any electrode deviation relying on a combination of the simple cases where the defects are taken individually. Our approach is validated by comparison between analytical and numerical results for defect sizes up to 4% of the trap radius. As described in Pedregosa-Gutierrez et al (2018 Rev. Sci. Instrum. 89 123101), an independent fine-tuning of the amplitude of the RF voltage applied on each electrode can be used to mitigate the geometrical defects of a realistic trap. In a different way than in Pedregosa-Gutierrez et al (2018 Rev. Sci. Instrum. 89 123101), the knowledge of an analytical equation for the potential allows to design the set of RF-voltages required for this compensation, based on the experimental measurement of the ion positions in the trap, without information concerning the exact position of each electrode, and with a small number of iterations. The requirements, performances and limitations of this protocol are discussed via comparison of numerical simulations and analytical results.

Active Trap Model.

Motivated by the dynamics of particles embedded in active gels, both invitro and inside the cytoskeleton of living cells, we study an active generalization of the classical trap model. We demonstrate that activity leads to dramatic modifications in the diffusion compared to the thermal case: the mean square displacement becomes subdiffusive, spreading as a power law in time, when the trap depth distribution is a Gaussian and is slower than any power law when it is drawn from an exponential distribution. The results are derived for a simple, exactly solvable, case of harmonic traps. We then argue that the results are robust for more realistic trap shapes when the activity is strong.

Study of deep level defects in InGaP/InGaAs-GaAsP/InGaAsN quantum well based multi-junction solar cell using finite element analysis

Degradation analysis of a quantum well-dilute nitride based multi-junction solar cell is presented using a 2D numerical device simulator: APSYS. By taking carrier removal effects into consideration, the proposed device exhibits strong electric field uniformity within the intrinsic region of the p-i-n middle cell. The electron traps are defined in the top InGaP and bottom InGaAsN base region considering 1 MeV electron irradiation in geostationary orbits. Considering thermionic emission, tunneling and SRH lifetime an effective lifetime value of 16.7 ps is considered in the middle MQW region. A record efficiency value of 38% and 44% is obtained at 1-sun and 500-sun AM0 spectrum respectively. The same efficiency value dropped by 4% by introducing a realistic SRV (1 × 104 cm s−1) and trap concentration values (1 × 1016 cm−3). Finally, we illustrate the influence of traps and lifetime on overall cell Jsc, Voc, η, and power density.

Experimental determination of Bose-Hubbard energies

We present the first experimental measurement of the ensemble averages of both the kinetic and interaction energies of the three-dimensional Bose--Hubbard model at finite temperature and various optical lattice depths across weakly to strongly interacting regimes, for an almost unit filling factor. The kinetic energy is obtained through Fourier transformation of a time-of-flight signal, and the interaction energy is measured using a newly developed atom-number-projection spectroscopy technique, by exploiting an ultra-narrow optical transition of two-electron atoms. The obtained experimental results can be used as benchmarks for state-of-the-art numerical methods of quantum many-body theory. As an illustrative example, we compare the measured energies with numerical calculations involving the Gutzwiller and cluster-Gutzwiller approximations, assuming realistic trap potentials and particle numbers at nonzero entropy (finite temperature); we obtain good agreement without fitting parameters. We also discuss the possible application of this method to temperature estimations for atoms in optical lattices using the thermodynamic relation. This study offers a unique advantage of cold atom system for `quantum simulators', because, to the best of our knowledge, it is the first experimental determination of both the kinetic and interaction energies of quantum many-body system.

Chiral topological phases in optical lattices without synthetic fields

Synthetic fields applied to ultracold quantum gases can realize topological phases that transcend conventional Bose and Fermi-liquid paradigms. Raman laser beams in particular are under scrutiny as a route to create synthetic fields in neutral gases to mimic ordinary magnetic and electric fields acting on charged matter. Yet external laser beams can impose heating and losses that make cooling into many-body topological phases challenging. We propose that atomic or molecular dipoles placed in optical lattices can realize a topological phase without synthetic fields by placing them in certain frustrated lattices. We use numerical modeling on a specific example to show that the interactions between dipolar fermions placed in a kagome optical lattice spontaneously break time reversal symmetry to lead to a topological Mott insulator, a chiral topological phase generated entirely by interactions. We estimate realistic entropy and trapping parameters to argue that this intriguing phase of matter can be probed with quantum gases using a combination of recently implemented technologies.

Fast manipulation of Bose–Einstein condensates with an atom chip

We present a detailed theoretical analysis of the implementation of shortcut-to-adiabaticity protocols for the fast transport of neutral atoms with atom chips. The objective is to engineer transport ramps with durations not exceeding a few hundred milliseconds to provide metrologically relevant input states for an atomic sensor. Aided by numerical simulations of the classical and quantum dynamics, we study the behavior of a Bose–Einstein condensate in an atom chip setup with realistic anharmonic trapping. We detail the implementation of fast and controlled transports over large distances of several millimeters, i.e. distances 1000 times larger than the size of the atomic cloud. A subsequent optimized release and collimation step demonstrates the capability of our transport method to generate ensembles of quantum gases with expansion speeds in the picokelvin regime. The performance of this procedure is analyzed in terms of collective excitations reflected in residual center of mass and size oscillations of the condensate. We further evaluate the robustness of the protocol against experimental imperfections.

Pattern and shape effects of orchid flower traps on attractiveness of Thrips palmi (Thysanoptera: Thripidae) in an orchid farm

Thrips palmi Karny is widely distributed and causes damage to orchid flowers. Orchid varieties in the genera Dendrobium and Mokara are different in shape. This study determined if different trap patterns which reflect flower shape may affect the attractiveness to thrips. The shapes of Dendrobium and Mokara orchid flowers were characterized and the numbers of flowers per raceme were counted in inflorescences in order to design realistic trap patterns. Four patterns (A, B, C and D) of flower traps were made by increasing the petal area. The mean number of T. palmi in flower pattern A was significantly lower than for flower patterns B, C and D (p < 0.05). The numbers of T. palmi in flower traps increased with flower petal area (r = 0.63, p < 0.05), but decreased with increasing length of flower contour (r = −0.56, p < 0.05). Six patterns (B1, B2, B3, B4, B5 and B6) of inflorescence traps were created by increasing the number of flowers per raceme. The numbers of T. palmi increased with increased numbers of flowers per raceme, pattern area and length of contour (r = 0.74, p < 0.05). Thus, inflorescence patterns and sizes affected the numbers of T. palmi attracted. The results of this research indicated that not only the patterns but also the sizes of traps were important factors for attractiveness to thrips. This information may be useful in designing and monitoring control programs for T. palmi.

Modelling water trap seal boundary conditions in building drainage systems: Computational fluid dynamics analysis of unsteady friction to improve accuracy

The safe removal of disease-carrying human waste is the objective of all sanitation systems and the limiting of air pressure transients within the system remains a significant part of current codes and regulations. The water trap seal offers fundamental protection and is the system’s sole barrier between the public sewer network and habitable space inside a building. Modelling water trap seal responses to air pressure fluctuations offers an opportunity to analyse whole system performance, but the quality of the data depends on the accuracy of the modelling technique and that of the defining inputs. AIRNET, a 1D Method of Characteristics based model, enables rapid whole system testing; however, the present boundary condition for the water trap seal within the model is based solely on steady state conditions, ignoring system dynamics. Computational fluid dynamics offers an opportunity to numerically evaluate the flow patterns within the trap seal in response to applied air pressure transients. This research confirms the importance of the rate of rise, and hence frequency of air pressure transients incident on water trap seals and relates this to potential vulnerabilities of different device geometries, particularly the ratio between inner and outer wall length. The research led to the development of a dynamic velocity decrement model encapsulating unsteady friction and separation losses linked to device geometry for the first time. The development of a frequency-dependent internal energy term Δ v, suitable for inclusion in AIRNET provides the capability to predict more realistic water trap response to air pressure transients over a range of air pressure transient frequencies likely to cause problems: 1 Hz to 8 Hz.Practical application: Whole system modelling can greatly improve the ability of design engineers to fully simulate the operation of a building drainage system in a realistic way. The work described in this paper improves the accuracy of whole system models by evaluating water dynamic responses to air pressure transients using a range of techniques including computational fluid dynamics and more traditional 1D finite difference method of characteristics models. The work also paves the way for more robust evaluation of building drainage products through in-depth investigation of the fluid mechanics associated with their operation.

Realistic Trap Configuration Scheme With Fabrication Processes in Consideration for the Simulations of AlGaN/GaN MIS-HEMT Devices

AlGaN/GaN metal-insulator-semiconductor high-electron mobility transistors (MIS-HEMTs) have become a promising candidate for use in efficient power conversion applications. However, under the practical HEMT device fabrication conditions, additional interfacial trap states generated by the fabrication process will strongly affect the device performance of the MIS-HEMTs. Such influences have so far been considered and modeled only at specific fabrication conditions. At the device design and simulation stage with various different processes, there lacks a simple and versatile scheme for a quick design evaluation. In this paper, we report a scheme of realistic trap configuration with fabrication process taken in consideration. This configuration is able to bring the simulation outcome closer to the actual device performance, which is largely affected by the interfacial trap conditions within various locations. The formation of the proposed configuration scheme started from the raw AlGaN/GaN wafer with transmission-line measurement patterns for 2-D electron gas charge density, followed by benchmarking the normally ON and normally OFF MIS-HEMTs devices made through actual fabrication processes. The relationship between interfacial trap density and fabrication processes was then identified. Finally, a test case on AlGaN/GaN inverter configuration involving both normally ON and normally OFF devices was used to demonstrate the effectiveness of the proposed scheme.

Fractional-charge vortex in a spinor Bose-Einstein condensate

We classify all possible fractional charge vortices of charge less than unity in spin-1 and spin-2 polar and cyclic Bose-Einstein condensates (BECs) with zero magnetization. Statics and dynamics of these vortices in quasi-two-dimensional spinor BECs are studied employing accurate numerical solution and a Lagrange variational approximation. The results for density and collective-mode oscillation are illustrated using fractional-charge BEC vortex of $^{23}$Na and $^{87}$Rb atoms with realistic interaction and trapping potential parameters.

Re-print of “Insight into the Resonance Ejection Process during Mass Analysis through Simulations for Improved Linear Quadrupole Ion Trap Mass Spectrometer Performance”

A methodology for the simulation of mass analysis of ions in RF ion traps is described and demonstrated. This methodology utilizes the very high computational throughput capabilities of a GPU to accelerate ion trajectory modeling by ∼10,000 fold over simple CPU based systems. This capability enables modeling of ion trajectories for realistic numbers of ions in realistic ion trap devices (defined by electrode structures and applied electrode voltages) and provides simulated mass spectral peaks as an end product. Comprehensive characterization of the effects on peak shape and resolution of electrode features such as slots or particular profiles, as well as critical operating parameters such as the amplitude and phase of the auxiliary voltages, is demonstrated. The simulated dependence of observed m/z peak resolution on auxiliary voltage phase and amplitude corresponds well with the results from a real commercial linear ion trap instrument. It is further confirmed via simulation that the extent of radial electrode displacement (stretch) for our commercial device corresponds to the minimum electrode displacement necessary to optimize m/z resolution. The results of a simulation study involving a set of 15 different ion trap configurations incorporating various trapping field compositions, electrode geometries, and applied voltages are presented. Several of the modeled trap configurations indicate the promise for improved m/z resolution.

Insight into the resonance ejection process during mass analysis through simulations for improved linear quadrupole ion trap mass spectrometer performance

A methodology for the simulation of mass analysis of ions in RF ion traps is described and demonstrated. This methodology utilizes the very high computational throughput capabilities of a GPU to accelerate ion trajectory modeling by ∼10,000 fold over simple CPU based systems. This capability enables modeling of ion trajectories for realistic numbers of ions in realistic ion trap devices (defined by electrode structures and applied electrode voltages) and provides simulated mass spectral peaks as an end product. Comprehensive characterization of the effects on peak shape and resolution of electrode features such as slots or particular profiles, as well as critical operating parameters such as the amplitude and phase of the auxiliary voltages, is demonstrated. The simulated dependence of observed m/z peak resolution on auxiliary voltage phase and amplitude corresponds well with the results from a real commercial linear ion trap instrument. It is further confirmed via simulation that the extent of radial electrode displacement (stretch) for our commercial device corresponds to the minimum electrode displacement necessary to optimize m/z resolution. The results of a simulation study involving a set of 15 different ion trap configurations incorporating various trapping field compositions, electrode geometries, and applied voltages are presented. Several of the modeled trap configurations indicate the promise for improved m/z resolution.

Conditions for diffusion-limited and reaction-limited recombination in nanostructured solar cells

The performance of Dye-sensitized solar cells (DSC) and related devices made of nanostructured semiconductors relies on a good charge separation, which in turn is achieved by favoring charge transport against recombination. Although both processes occur at very different time scales, hence ensuring good charge separation, in certain cases the kinetics of transport and recombination can be connected, either in a direct or an indirect way. In this work, the connection between electron transport and recombination in nanostructured solar cells is studied both theoretically and by Monte Carlo simulation. Calculations using the Multiple-Trapping model and a realistic trap distribution for nanostructured TiO2 show that for attempt-to-jump frequencies higher than 10(11)-10(13) Hz, the system adopts a reaction limited (RL) regime, with a lifetime which is effectively independent from the speed of the electrons in the transport level. For frequencies lower than those, and depending on the concentration of recombination centers in the material, the system enters a diffusion-limited regime (DL), where the lifetime increases if the speed of free electrons decreases. In general, the conditions for RL or DL recombination depend critically on the time scale difference between recombination kinetics and free-electron transport. Hence, if the former is too rapid with respect to the latter, the system is in the DL regime and total thermalization of carriers is not possible. In the opposite situation, a RL regime arises. Numerical data available in the literature, and the behavior of the lifetime with respect to (1) density of recombination centers and (2) probability of recombination at a given center, suggest that a typical DSC in operation stays in the RL regime with complete thermalization, although a transition to the DL regime may occur for electrolytes or hole conductors where recombination is especially rapid or where there is a larger dispersion of energies of electron acceptors.

Nanoscale Heat Engine Beyond the Carnot Limit

We consider a quantum Otto cycle for a time-dependent harmonic oscillator coupled to a squeezed thermal reservoir. We show that the efficiency at maximum power increases with the degree of squeezing, surpassing the standard Carnot limit and approaching unity exponentially for large squeezing parameters. We further propose an experimental scheme to implement such a model system by using a single trapped ion in a linear Paul trap with special geometry. Our analytical investigations are supported by MonteCarlo simulations that demonstrate the feasibility of our proposal. For realistic trap parameters, an increase of the efficiency at maximum power of up to a factor of 4 is reached, largely exceeding the Carnot bound.

Squeezing in Bose–Einstein condensates with large numbers of atoms

We examine the feasibility of creating and measuring large relative number squeezing in multicomponent trapped Bose–Einstein condensates. In the absence of multimode effects, this squeezing can be arbitrarily large for arbitrarily large condensates, but a range of processes limit the measurable squeezing in realistic trap configurations. We examine these processes, and suggest methods to mitigate them. We conclude that high levels of squeezing with large numbers of atoms is feasible, but can realistically only be achieved in particular trap geometries. We also introduce a method of maximizing the measurable squeezing by using a π-pulse during the process to improve spatial mode-matching.

Design and Optical Trapping of a Biocompatible Propeller-like Nanoscale Hybrid

Designing nanoscale objects with the potential to perform externally controlled motion in biological environments is one of the most sought-after objectives in nanotechnology. Different types of chemically and physically powered motors have been prepared at the macro- and microscale. However, the preparation of nanoscale objects with a complex morphology, and the potential for light-driven motion has remained elusive to date. Here, we go a step forward by designing a nanoscale hybrid with a propeller-resembling shape, which can be controlled by focused light under biological conditions. Our hybrid, hereafter "Au@DNA-origami", consists of a spherical gold nanoparticle with self-assembled, biocompatible, two-dimensional (2D) DNA sheets on its surface. As a first step toward the potential utilization of these nanoscale objects as light-driven assemblies in biological environments, we show that they can be optically trapped, and hence translated and deposited on-demand, and that under realistic trapping conditions the thermally induced dehybridization of the DNA sheets can be avoided.

Ising antiferromagnet with ultracold bosonic mixtures confined in a harmonic trap

We present accurate results based on Quantum Monte Carlo simulations of two-component bosonic systems on a square lattice and in the presence of an external harmonic confinement. Starting from hopping parameters and interaction strengths which stabilize the Ising antiferromagnetic phase in the homogeneous case and at half integer filling factor, we study how the presence of the harmonic confinement challenge the realization of such phase. We consider realistic trapping frequencies and number of particles, and establish under which conditions, i.e. total number of particles and population imbalance, the antiferromagnetic phase can be observed in the trap.

Finite-temperature study of Bose-Fermi superfluid mixtures

Ultra-cold atom experiments offer the unique opportunity to study mixing of different types of superfluid states. Our interest is in superfluid mixtures comprising particles with different statistics- Bose and Fermi. Such scenarios occur naturally, for example, in dense QCD matter. Interestingly, cold atomic experiments are performed in traps with finite spatial extent, thus critically destabilizing the occurrence of various homogeneous phases. Critical to this analysis is the understanding that the trapped system can undergo phase separation, resulting in a unique situation where phase transition in either species (bosons or fermions) can overlap with the phase separation between possible phases. In the present work, we illustrate how this intriguing interplay manifests in an interacting 2-species atomic mixture - one bosonic and another fermionic with two spin components - within a realistic trap configuration. We further show that such interplay of transitions can render the nature of the ground state to be highly sensitive to the experimental parameters and the dimensionality of the system.

Production of entanglement in Raman three-level systems using feedback

We examine the theoretical limits of the generation of entanglement in a damped coupled ion-cavity system using jump-based feedback. Using Raman transitions to produce entanglement between ground states reduces the necessary feedback bandwidth, but does not improve the overall effect of the spontaneous emission on the final entanglement. We find that the fidelity of the resulting entanglement will be limited by the asymmetries produced by vibrations in the trap, but that the concurrence remains above 0.88 for realistic ion trap sizes.