Realization of a mirror magneto-optical trap

Abstract

We present details for construction and the operation of a mirror magneto-optical trap for cooling and trapping rubidium atoms. For trap operation, only four input laser beams are needed in contrast to the normal six for a standard trap. In excess of 10⁸ atoms have been trapped with this arrangement, with the atomic ensemble only ～1mm from the surface of a reflective mirror. This trap is highly suited to studies of magnetic guiding and magnetic manipulation of cold atomic ensembles.     

A two species trap for chromium and rubidium atoms

Abstract

We realize a combined trap for bosonic chromium (⁵²Cr) and rubidium (⁸⁷Rb) atoms. Initial experiments focus on exploring a suitable loading scheme for the combined trap and on studies of new trap loss mechanisms originating from simultaneous trapping of two species. By comparing the trap loss from the ⁸⁷Rb magneto-optical trap (MOT) in the absence and presence of magnetically trapped ground state ⁵²Cr atoms we determine the scattering cross-section of σ _inel,RbCr = 5.0 ± 4.0 × 10^?18 m² for light-induced inelastic collisions between the two species. Studying the trap loss from the Rb magneto-optical trap induced by the Cr cooling-laser light, the photoionization cross-section of the excited 5P_3/1 state at an ionizing wavelength of 426 nm is measured to be σ _P = 1.1 ± 0.3 × 10^?21 m².     

Vortices in a stirred Bose-Einstein condensate

Abstract

We stir with a focused laser beam a Bose-Einstein condensate of ⁸⁷Rb atoms confined in a magnetic trap. We observe the formation of a single vortex for a stirring frequency exceeding a critical value. At larger rotation frequencies we produce states of the condensate for which up to eleven vortices are simultaneously present. We present measurements of the decay of a vortex array once the stirring laser beam is removed.     

Controlled simultaneous rotation of multiple optically trapped particles

Abstract

We present a method for the controlled alignment or rotation of birefringent particles trapped in multiple optical trap sites of an interference pattern between two Laguerre—Gaussian laser modes. Controlled spin or alignment of the particles within each individual trap site is achieved independently of the lateral or rotational motion of the interference pattern as a whole. This technique may lead to driving arrays of micro-machines and micro-fluidic studies and can be used in combination with dynamically generated trapping arrays for uniformly distributed stirring throughout microscopic volumes of fluid.     

Preparation, Optical Absorption, Photoconductivity, and Thermally Stimulated Conductivity of ZnGa2Se4

The optical absorption, photoconductivity, and thermally stimulated current (TSC) spectra of ZnGa₂Se₄ were measured. The results demonstrate that the optical transitions at point (000) for the E c polarization have the lowest energy. TSC data point to a trap depth of 0.24 eV and a quasi-continuous trap distribution centered at 0.49 eV. The 2.23- and 2.10-eV peaks in the spectral dependence of the photocurrent are attributed to electron transitions from the valence band to the trap level located 0.24 eV below the conduction-band minimum and to the quasi-continuously distributed trap levels around 0.49 eV.     

Three-dimensional force calibration of optical tweezers

Abstract

We demonstrate a method for 3-dimensional force calibration of optical tweezers by recording the trapping dynamics of polystyrene beads. This is realized by time-resolved detection of the horizontal and vertical position of a bead which is drawn to the focus of a laser beam. The method provides real time characterization of the force profile of an optical trap in all directions.     

How to catch an atom with single photons

Abstract

We report on trapping a single neutral atom in the standing-wave light field of a high-finesse optical cavity containing one photon on average, a single-photon optical trap, or SPOT for short. This trap has the novel feature that the light field is also used to observe the atom in real time. The oscillatory motion of the trapped atom induces well-resolved oscillations of the light intensity. Periodic structure is visible in the fourth-order intensity correlation function, attributed to long-distance flights of the atom along the standing wave. The finite duration of those flights provides evidence for cavity-mediated cooling of atoms. We discuss the various mechanisms determining the trapping time and compare the results with a quantum-jump Monte Carlo simulation to interpret the observed signals.     

Particle number fluctuations in an ideal Bose gas

Abstract

We analyse occupation number fluctuations of an ideal Bose gas in a trap which is isolated from the environment with respect to particle exchange (canonical ensemble). We show that in contrast to the predictions of the grandcanonical ensemble, the counting statistics of particles in the trap ground state changes from monotonously decreasing above the condensation temperature to single-peaked below that temperature. For the exactly solvable case of a harmonic oscillator trapping potential in one spatial dimension we extract a Landau–Ginzburg functional which–despite the non-interacting nature of the system–displays the characteristic behaviour of a weakly interacting Bose gas. We also compare our findings with the usual treatment which is based on the grand-canonical ensemble. We show that for an ideal Bose gas neither the grand-canonical and canonical ensemble thermodynamically equivalent, nor the grand-canonical ensemble can be viewed as a small system in diffusive contact with a particle reservoir.     

Entangling atoms and ions in dissipative environments

Abstract

Quantum information processing rests on our ability to manipulate quantum superpositions through coherent unitary transformations, and to establish entanglement between constituent quantum components of the processor. The quantum information processor (a linear ion trap, or a cavity confining the radiation field for example) exists in a dissipative environment. We discuss ways in which entanglement can be established within such dissipative environments. We can even make use of a strong interaction of the system with its environment to produce entanglement in a controlled way.     

Microcomputer loop communication network design

Abstract

An optical illumination method was used to examine the relationship between the variation of capacitance and the interface trap states of an MOS capacitor after various charge‐temperature agings. The peaks in the illumination‐induced capacitance‐voltage curves were found to be caused neither by the lateral nonuniformities of interface charges nor by the nonuniformities of the illumination intensities, but by the existence of interface trap states. This can be used as a quick method to directly identify the interface trap states.     

Orientation of biological cells using plane-polarized gaussian beam optical tweezers

Abstract

Optical tweezers are widely used for the manipulation of cells and their internal structures. However, the degree of manipulation possible is limited by poor control over the orientation of the trapped cells. We show that it is possible to controllably align or rotate disc-shaped cells—chloroplasts of Spinacia oleracea—in a plane-polarized Gaussian beam trap, using optical torques resulting predominantly from circular polarization induced in the transmitted beam by the non-spherical shape of the cells.     

Ultra-stable Hg+

Abstract

We report the development of a fieldable frequency standard based on ¹⁹⁹Hg⁺ ions confined in a hybrid r.f./dc linear ion trap. This trap permits storage of large numbers of ions with reduced susceptibility to the second-order Doppler effect caused by the r.f. confining fields. A 160 mHz wide atomic resonance line for the 40·5 GHz clock transition is used to steer the output of a 5 MHz crystal oscillator to obtain a stability of 2 × 10^?15 for 24 000 s averaging times. For longer averaging intervals, measurements are limited by instabilities in available hydrogen maser frequency standards. Measurements with 37 mHz linewidth for the Hg⁺ clock transition demonstrate that the inherent stability for this frequency standard is at least as good as 1 × 10^?15.     

Switching and self-trapping dynamics of bose-Einstein solitons

Abstract

We investigate the dynamics of two weakly coupled Bose condensates in long cigar-shaped traps. The Bose condensates are characterized by attractive mean-field interaction and consequently can be studied in terms of bright solitons. We exploit the analogy with directional fibre couplers in nonlinear fibre optics to uncover interesting dynamical regimes like switching of condensates from one trap to another and self-trapping of condensates. We also discuss the analogy between two weakly coupled Bose condensates and the Josephson junction in superfluids and superconductors.     

On the Isolated Pentagon Rule: Could Fullerenes Exist Violating This Rule?

Abstract

Through a short review on pentalene chemistry, it is discussed the possibility to trap as organometallic complexes unstable fullerenes violating the isolated pentagons rule.     

Emission and Absorption Properties of Atoms in a Trapping Potential

Abstract

We investigate the resonance fluorescence emission and absorption spectra for a one-dimensional harmonically trapped two-level ion. The master equation is used to generate the atomic polarizations from which the spectra are derived. Because of their size, the final density matrix equations are investigated numerically. The calculations are carried out in the Lamb-Dicke limit of tight localization of the ion. Sharp peaks are found to appear in the spectra at frequencies detuned from line centre by steps of the trap frequency. The frequency of the peaks and their superposition with Rabi sidebands above saturation are analysed for a variety of parameter ranges. Moreover, new features of the absorption spectra of a weak probe such as sharp gain regions around the trap sidebands are also discussed.     

In-flight Capture of an Ion Beam in a Paul Trap

Abstract

A system for collecting 60 keV ion beams was set up at the ISOLDE-3 radionuclide mass-separator facility at CERN. Electric field retardation was used to bring the ions to 20 eV for injection into a Paul trap. Tests were made with ¹³²Xe⁺ and ⁷⁹Br^? ions. A trap potential well depth of about 30 V could be created. At this well depth a collection efficiency of about 0·2% was obtained for a xenon beam of emittance about 2π mm-mrad and energy spread estimated to be of a few electronvolts. The efficiency for bromine ions was less, but still appreciable. The efficiencies achieved indicate that a sizeable fraction of the ions arriving at the correct rf window for acceptance by the trap were being collected. To the limit of the apparatus, the efficiency was increasing in proportion to the third power of the rf amplitude applied to the trap, indicating that it was proportional to the phase space volume of the trap. These results are now being used to design a larger Paul trap collection system for installation at the ISOLDE-BOOSTER facility. By including a pre-bunching system to fit an incoming dc beam to the rf acceptance, it is expected that almost complete collection of weak mass-separated high-velocity beams can be achieved.     

Investigations on the Kinetic Energy of Trapped Ions by Consideration of Ion/Molecule Collisions

Abstract

To utilize the capabilities of the r.f. ion trap for high-precision spectroscopy and for the study of ion/molecule collisions, the kinetic energy of the ion cloud must be known as precisely as possible. One method for the determination of ion cloud kinetic energy is to measure the rate constant of a given reaction. We have investigated this method under ultra-high vacuum conditions which are those used in spectroscopic experiments and studies of ions in dilute media.     

Experimental preparation and measurement of quantum states of motion of a trapped atom

Abstract

We report the creation and full determination of several quantum states of motion of a ⁹Be⁺ ion bound in a RF (Paul) trap. The states are coherently prepared from an ion which has been initially laser cooled to the zero-point of motion. We create states having both classical and non-classical character including thermal, number, coherent, squeezed, and ?Schrödinger cat‘ states. The motional quantum state is fully reconstructed using two novel schemes that determine the density matrix in the number state basis or the Wigner function. Our techniques allow well controlled experiments decoherence and related phenomena on the quantum-classical borderline.     

Rotation of microparticles with Bessel beams generated by diffractive elements

Abstract

We show that imaging a non-diverging Bessel beam by a spherical lens leads to the generation of a diverging Bessel beam. Expressions for the projections of the Umov-Poynting vector for a two-dimensional TE-polarized Bessel beam and a three-dimensional paraxial linearly polarized Bessel beam are derived. A fifth-order Bessel beam is produced using a single optical element-a 16-level phase-only diffractive helical axicon fabricated using electron beam lithography. This beam was successfully used to trap and rotate 5-10 μm diameter yeast particles and polystyrene beads of diameter 5 μm.     

The design of a multi‐speed PSK modem

Abstract

Charge‐temperature, modified from bias‐temperature, technique is presented for the investigation of the interface properties of Al‐SiO₂‐Si (P) MOS capacitors. By using this technique, the change of interface trap states was found to be related to the treatment of charge‐temperature agin gand consequently the distribution of the mobile charges inside the oxide. An equivalent equation is expressed for the evaluation of interface trap states from the measured C‐V data. In addition, a two‐region model describing the distributions of the mobile charges of the capacitor after various charge‐temperature agings is proposed for the experimental observations. And the fitting results indicate that the effective Debye length due to interface trap states is about 20 Å.