Ring-shaped Trap Research Articles

The Interference Effect of a Bose—Einstein Condensate in a Ring-Shaped Trap

We have studied the interference effect of a Bose—Einstein condensate expanding in a ring-shaped trap. The dynamic process of the condensate is analyzed based on the Gross—Pitaevskii equation. Our numerical results show that a petal-like interference pattern is formed during expansion within the ring-shaped trap. The petal number depends on the evolution time, which can be well explained by the interference of two flows of the condensate.

Gold Nanoparticle-Induced Formation of Artificial Protein Capsids

Gold nanoparticles are generally considered to be biologically inactive. However, in this study we show that the addition of 1.4 nm diameter gold nanoparticle induces the remodeling of the ring-shaped protein TRAP into a hollow, capsid-like configuration. This structural remodeling is dependent upon the presence of cysteine residues on the TRAP surface as well as the specific type of gold nanoparticle. The results reveal an apparent novel catalytic role of gold nanoparticles.

Bose-Einstein condensates in a ring-shaped trap with a nonlinear double-well potential

We develop the mean-field theory for Bose-Einstein condensates in a one-dimensional ring with two types of nonlinear double-well potentials, based on a pair of $\ensuremath{\delta}$ functions or Gaussian of a finite width, placed at diametrically opposite points. By analyzing the ground states (GSs) in these cases, we find a qualitative difference between them. With the Gaussian profile, the GS always undergoes the phase transition from the symmetric shape to an asymmetric one at a critical value of the norm. In contrast, the symmetry-breaking transition does not happen with the $\ensuremath{\delta}$-functional profile of the nonlinearity, and the GS always remains symmetric. In addition, the numerical analysis for the Gaussian profile demonstrates that the type of symmetry-breaking transition depends on the width of the nonlinear-potential well.

From rotating atomic rings to quantum Hall states

Considerable efforts are currently devoted to the preparation of ultracold neutral atoms in the strongly correlated quantum Hall regime. However, the necessary angular momentum is very large and in experiments with rotating traps this means spinning frequencies extremely near to the deconfinement limit; consequently, the required control on parameters turns out to be too stringent. Here we propose instead to follow a dynamic path starting from the gas initially confined in a rotating ring. The large moment of inertia of the ring-shaped fluid facilitates the access to large angular momenta, corresponding to giant vortex states. The trapping potential is then adiabatically transformed into a harmonic confinement, which brings the interacting atomic gas in the desired quantum-Hall regime. We provide numerical evidence that for a broad range of initial angular frequencies, the giant-vortex state is adiabatically connected to the bosonic ν = 1/2 Laughlin state.

Phase fluctuations in anisotropic Bose-Einstein condensates: From cigars to rings

We study the phase-fluctuating condensate regime of ultra-cold atoms trapped in a ring-shaped trap geometry, which has been realized in recent experiments. We first consider a simplified box geometry, in which we identify the conditions to create a state that is dominated by thermal phase-fluctuations, and then explore the experimental ring geometry. In both cases we demonstrate that the requirement for strong phase fluctuations can be expressed in terms of the total number of atoms and the geometric length scales of the trap only. For the ring-shaped trap we discuss the zero temperature limit in which a condensate is realized where the phase is fluctuating due to interactions and quantum fluctuations. We also address possible ways of detecting the phase fluctuating regime in ring condensates.

Erratum: Exploiting the composite character of Rydberg atoms for cold-atom trapping [Phys. Rev. A79, 041403 (2009)

In our paper, the calculation of the dressed ground state surface for the case of a strong gradient field B=1 G and G =5 Tm−1; results shown in Fig. 2 b and d of the original publication is incomplete. In detail, emergent two-photon couplings between the 5S1/2 ,F=mF=2 ground state and 5S1/2 ,F=2,mF 2 levels via the hyperfine levels of the 5P3/2 excited state due to the first excitation laser have been omitted in the original publication. Including these states in our calculations, it turns out that the spatial dependence of the light shift is not strong enough to entail the ring-shaped trapping potential as originally presented in Figs. 2 b and d . The results presented in the regime of strong Ioffe fields B=10 G and G=5 Tm−1; results shown in Fig. 2 a and c of the original publication do not change: In this case, the couplings with the 5S1/2 ,F=2,mF 2 levels are negligible and the simplified 3-level scheme as described in the original publication holds. Consequently, the conclusion that the specific signatures of the Rydberg trapping potential can be probed by means of ground state atoms that are off-resonantly coupled to the Rydberg state via a two photon laser transition does not change. The conclusion of our original publication that the composite nature of Rydberg atoms significantly alters their trapping properties opposed to pointlike particles with the same magnetic moment is not affected by the changes described in this erratum. Moreover, we would like to correct two minor typos of our original publication. Firstly, the off-diagonal matrix elements of Eq. 7 should read /2 instead of − /2. The eigenvalues of the matrix and hence the dressed surfaces are not affected by this change of sign. Secondly, Ẽp= B R instead of Ẽp=2 B R ; in our calculations Ẽp was implemented correctly. PHYSICAL REVIEW A 80, 029903 E 2009

Far-off-resonant ring trap near the ends of optical fibers

We propose that micrometer-sized atom traps can be created using the optical dipole force between the ends of two single-mode optical fibers carrying counterpropagating light beams of two different wavelengths from both fibers. The traps have a simple design that is feasible to implement with commercially available products. They can be used as a flexible ``atom tweezer'' to manipulate atoms in free space without the need for traditional focused laser beams. A particularly interesting feature is the formation of a static ring-shaped trap for properly chosen beam parameters. Furthermore, this ring can be split into two longitudinally adjacent rings. Microscopic ring traps such as this could have important applications in atom interferometry and fundamental investigations of Bose-Einstein condensates.

High-throughput sorting and analysis of human sperm with a ring-shaped laser trap

Sperm motility is an important concept in fertility research. To this end, single spot laser tweezers have been used to quantitatively analyze the motility of individual sperm. However, this method is limited with throughput (single sperm per spot), lacks the ability of in-situ sorting based on motility and chemotaxis, requires high laser power (hundreds of milliWatts) and can not be used to dynamically monitor changes in sperm swimming behavior under the influence of a laser beam. Here, we report a continuous 3-D ring-shaped laser trap which could be used for multi-level and high-throughput (tens to hundred sperm per ring) sperm sorting based on their motility and chemotaxis. Under a laser power of only tens of milliWatts, human sperm with low to medium velocity are slowed down, stopped, or forced to change their trajectories to swim along the ring due to the optical gradient force in the radial direction. This is the first demonstration of parallel sperm sorting based on motility with optical trapping technology. In addition, by making the sperm swimming along the circumference of the ring, the effect of laser radiation, optical force and external obstacles on sperm energetics are investigated in a more gentle and quantitative way. The application of this method could be extended to motility and bio-tropism studies of other self-propelled cells, such as algae and bacteria.

Size tunable three-dimensional annular laser trap based on axicons

A three-dimensional (3D) ring-shaped laser trap has been built using axicons. The diameter of this laser trap ranges from 70 to 140 mum and is adjusted by simply changing the position of one axicon in the optical path. Parallel 3D trapping of 5 mum silica microspheres and 3D confinement of cells along the ring are demonstrated. In this system the special optical properties of axicons are used to create a continuous annular trap with high power efficiency and a constant numerical aperture. This new approach, without any mechanical scanning, offers significant potential for applications in cell motility analysis and biotropism studies.

Some properties of ion trajectories in the radial plane of an axially symmetric ion trap.

In this article we analyse the trajectories of externally generated ions injected in the radial plane into the ion trap. The shape of the envelope curves for two-dimensional (2D) ion trajectories is determined. Conditions under which these envelope curves can be transformed into circles are found. We show that the amplitude of ion oscillations is a minimum in this case and that this mode corresponds to optimised ion trapping conditions. Also we discuss a ring-shaped ion trap mass spectrometer electrode system which consists of two ring electrodes, and which utilises ion trajectories with circular envelope curves.

Atomic density and temperature distributions in magneto-optical traps

A theoretical investigation into density, pressure, and temperature distributions in magneto-optical traps is presented. After a brief overview of the forces that arise from reradiation and absorption, a condition that the absorptive force be conservative is used to show that, if the temperature is uniform throughout the trap, any density solutions to the force equations will not be physical. Further, consistent density solutions are unlikely to exist at all. In contrast, with a varying temperature reasonable solutions are demonstrated, with some restrictions. Doppler forces involved in ring-shaped trap structures are used to calculate orbit radii in racetrack geometry traps, and corrections to the present discrepancy between theoretical and experimental studies are discussed in the context of reradiation and diffusion.

Influence of the number of atoms in a ring-shaped magneto-optical trap: Observation of bifurcation

The spatial ring-shaped distribution of atoms in a magneto-optical trap, produced by misaligned Gaussian laser beams, is investigated with respect to the increase in the number of trapped atoms. Experimental observation of the bifurcation of a single ring into a double-ring structure is reported and explained using a model that includes radiation force due to reabsorption of photons together with the conventional radiative force.

Time of flight technique to determine temperature of atoms in a ring-shaped trap

Spatial ring-shaped distribution of atoms in magneto-optical traps can be produced when the Gaussian laser beams used in the trap are misaligned as in a race-track geometry. We use a new version of the time of flight technique to determine the temperature and velocity distribution of the atoms in the ring. We found results which are consistent with the Doppler theory of laser cooling.

The effects of electrostatic, molecular drag and gravitational forces on the behavior of particle clouds in an RF discharge

A Gaseous Electronics Conference (GEC) Reference Cell was used to investigate the behavior of graphite particles sputtered in an argon plasma. By configuring the reactor in a normal (wafer facing upward) and in an inverted (wafer facing downward) configuration, and by varying the direction and flow of the argon, the relative importance of gravity, molecular drag and electrostatic trapping could be observed. It was observed that particle clouds in specific locations adjacent to the wafer (referred to as particle traps) were identical in both configurations. Drag forces from the showerhead grounded electrode were sufficient to prevent particles from accumulating in the traps over the wafer. Drag forces from flow parallel to the wafer (/spl ges/25 cm/s) easily emptied the traps. Gas flow from a ring source mounted above a downward facing driven electrode were observed to affect the manner in which particles were removed from the ring-shaped trap surrounding the cathode. In that case, particles were observed to flow down eight fluid streamlines toward the eight openings through which the gas flowed from the reaction chamber to the pump. Comparison of results for the normal and inverted configurations also permitted estimates of the number of electrons attached to each particle.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>