A broad emitter diode laser system for lithium spectroscopy

7 Li atoms. With 70 mW of laser power, 10⁷ atoms have been loaded from a nearby thermal source. Received: 19 January 1998     

Writing a superlattice with light forces

In atom lithography the conventional roles played by light and matter are reversed. Instead of using a solid mask to pattern a light beam, a mask of light is used to pattern a beam of neutral atoms. In this paper we report the production of different chromium dot arrays with quadratic symmetry. The lattice period depends on the relative polarization and the phase of the two standing waves generating the light mask. A small angular misalignment of the laser beams breaks the high symmetry and a chromium superlattice is written, that is a continuous periodic change between two different quadratic lattices. The structures exhibit lines with a FWHM below 50 nm and clearly separated chromium dots with a FWHM below 70 nm. Received: 30 September 1999 / Revised version: 14 February 2000 / Published online: 5 April 2000     

Ion strings for quantum gates

Received: 6 August 1997/Revised version: 21 October 1997     

Five-beam magneto-optical trap and optical molasses

We have operated a magneto-optical trap and optical molasses for the laser cooling of cesium atoms on the basis of a five-beam laser configuration. For the magneto-optical trap two laser beams counterpropagate along the axis of a quadrupole trap and the remaining three beams propagate in the orthogonal plane at 120° to each other. The same optical configuration was used for the optical molasses. We have tested the efficiency in atom collection and the temperatures reached in both cooling processes. In comparison to previous results on a six-beam configuration, a lower number of atoms is collected, while comparable densities are realized. The atomic temperatures have been measured through a delayed shadow-image technique, where one of the running-wave cooling beams produces an absorptive image of the atoms on a camera. Received: 14 January 1999 / revised version: 23 June 1999 / Published online: 8 September 1999     

High-resolution atomic channeling using. velocity-selected atomic beam

High-resolution atomic channeling using velocity-controlled atoms may be able to overcome precision limitations of the conventional atom lithography. We have experimentally clarified the dependence of line width and contrast of atomic patterns in the channeling region on the velocity spread of the atomic source for the first time. Thermal or velocity-selected atomic beams prepared with a one-dimensional magneto-optical trap were employed as the atomic sources. We investigated the channeling characteristics by measuring the frequency shifts of the atomic absorption spectra in an intense standing wave light field. As a result, we can show that narrower line width and higher contrast atomic patterns are obtained as the velocity spread becomes narrower. An atomic pattern with an estimated line width of 57 nm was generated when the velocity spread of the atomic source was almost 50 m/s, that is, 1/6 that of the thermal beam. Received: 16 June 2001 / Published online: 7 November 2001     

Laser cooling of atoms in optical lattices including quantum statistics and dipole–dipole interactions

We develop a mean-field approach to include dipole-dipole interactions and quantum statistics in the atomic dynamics in bright and dark optical lattices including the proper spatial potentials instead of a simple δ-approximation. For classical distinguishable particles the results are even quantitatively similar to the properly scaled δ-function model. As the dominant effect bright and dark lattices exhibit opposite shifts in the lattice band energies and differ in their localisation properties as a function of density. The spatial-dependent potential allows strong modifications also in dark lattices, but the main conclusions obtained in the δ-approximation turn out to be still valid. Interestingly, important quantitative differences from the δ-model can occur as far as the effect of statistics in concerned, especially for fermions. We study the quantum statistical effects as a function of detuning and lattice well depths and identify the case of lattices with deep wells and large detunings as the preferred parameter region to observe them. Received 24 November 1999 / revised version: 24 June 1999 / Published online: 8 September 1999     

Collisional effects on the collective laser cooling . of trapped bosonic gases

We analyse the effects of atom–atom collisions on a collective laser cooling scheme. We derive a quantum master equation which describes the laser cooling in presence of atom–atom collisions in the weak-condensation regime. Using such equation, we perform Monte Carlo simulations of the population dynamics in one and three dimensions. We observe that the ground-state laser-induced condensation is maintained in the presence of collisions. Laser cooling causes a transition from a Bose–Einstein distribution describing collisionally induced equilibrium, to a distribution with an effective zero temperature. We analyse also the effects of atom–atom collisions on the cooling into an excited state of the trap. Received: 18 June 1999 / Revised version: 24 September 1999 / Published online: 10 November 1999     

An optical conveyor belt for single neutral atoms

Using optical dipole forces we have realized controlled transport of a single or any desired small number of neutral atoms over a distance of a centimeter with sub-micrometer precision. A standing wave dipole trap is loaded with a prescribed number of cesium atoms from a magneto-optical trap. Mutual detuning of the counter-propagating laser beams moves the interference pattern, allowing us to accelerate and stop the atoms at preselected points along the standing wave. The transportation efficiency is close to 100%. This optical ‘single-atom conveyor belt’ represents a versatile tool for future experiments requiring deterministic delivery of a prescribed number of atoms on demand. Received: 6 July 2001 / Published online: 23 November 2001     

Decoding the dynamics of a single trapped atom from photon correlations

Received: 4 September 1998     

Laser-induced hybrid trap for micro-bubbles

Micro-bubbles have been stably trapped in liquid ethanol by a focused argon laser beam. Two equilibrium points where bubbles can be trapped are observed to be at the center and the rim of the laser beam. The light force is also able to push a bubble into the liquid to a position well below the liquid surface. Both the light-pressure force and the fluid force induced by the convection of the liquid medium are calculated. The results clearly show that these two kinds of forces account for the formation of trapping potential. Received: 3 February 2000 / Revised version: 6 July 2000 / Published online: 8 November 2000     

Laser cooling in a CO2-laser optical lattice

Received: 19 June 1998     

Nanoscale focusing of atoms with a pulsed standing wave

We have theoretically and experimentally investigated the focusing properties of a detuned pulsed standing wave onto a beam of neutral atoms. In close analogy to the continuous-wave situation the dipole force leads to a periodic focusing of atoms with a period of λ/2, provided an adiabatic condition is fulfilled. Pulsed laser light is conveniently converted to short wavelengths and hence offers advantages in the application of atom lithography with elements of technological interest having blue or UV resonance lines. Received: 6 October 1999 / Revised version: 3 February 2000 / Published online: 5 April 2000     

Rb atomic absorption line reference for single Sr+ laser cooling systems

85 Rb, 5s²S_1/2(F”=2)→6p²P_1/2(F’=2,3) absorption resonance with the ⁸⁸Sr⁺, 5s²S_1/2→5p²P_1/2 transition is exploited to provide a simple, effective frequency reference for a laser cooling/fluorescence excitation source applied to single Sr⁺ ions. A modulation-free frequency stabilization system has been designed which uses the differential signal from two frequency-displaced beams traversing a Rb cell and which probe the Doppler-broadened Rb S–P lineshape at microwatt power levels. The method is applied to frequency lock a 422-nm frequency-doubled diode laser system that is used for excitation of a single ⁸⁸Sr⁺ ion. Stable, long-term laser cooling and fluorescence are achieved using the frequency-stabilized 422-nm source resulting in observed ion confinement times without adjustment of over 8 h, together with an improvement in single-ion loading efficiency. Received: 12 February 1998     

Phonon–phonon interactions due to non-linear effects in a linear ion trap

We examine in detail the theory of the intrinsic non-linearities in the dynamics of trapped ions due to the Coulomb interaction. In particular, the possibility of mode–mode coupling, which can be a source of decoherence in trapped ion quantum computation, or can be exploited for parametric down-conversion of phonons, is discussed and conditions under which such coupling is possible are derived. Received: 8 November 2002 / Published online: 26 March 2003 RID="*" ID="*"Permanent address: MIP, Université Pierre et Marie Curie and Département de Physique, école Normale Supérieure, 75005 Paris, France RID="**" ID="**"Corresponding author. Fax: +1-505/667-1931, E-mail: dfvj@lanl.gov     

Endoscopy in the Paul trap: The influence of the micromotion

We show that three real-valued parameters govern the quantum motion of an ion stored in the Paul trap. These parameters are two angles of rotation in phase space and a squeezing parameter. The time dependence of these parameters simplifies considerably using Floquet solutions. This allows us to use the method of quantum state endoscopy to measure a pure state of the vibratory motion of an ion taking into account the full time dependence of the trapping potential. Received: 19 June 1996     

Two dimension selective coherent population trapping controlled by a phase shift

Two-dimensional laser cooling based on velocity-selective coherent population trapping is investigated theoretically for the J _g=1J _e=0 atomic transition. Wavevectors and polarizations of three laser beams are chosen to realize a coherent superposition of three degenerate ground states. For the first time in laser cooling, use is made of the electric field phases to realize coherent population trapping selective in two dimensions. Numerical solutions and analytic estimates are presented for laser cooling of helium atoms.     

Observation of collimation and decollimation of an atomic beam in a misaligned standing wave

This paper reports an experimental study on the collimation and decollimation of an atomic beam in a misaligned standing wave, in which the effective detuning caused by the Doppler effect is affected by the longitudinal velocity of the atomic beam. The experiment shows that in a strong field with red detuning between laser field and atomic transition frequency, laser heating in a normal standing wave becomes laser cooling in a misaligned standing wave for an approriate misalignment angle. For blue detuning, laser cooling in a standing wave can also become laser heating in a misaligned standing wave for an appropriate condition. These results ca be used in controling atomic motion.     

The ion trap quantum information processor

Received: 16 October 1996/Revised version: 2 April 1997     

Simulation of Chromium Atom Deposition Pattern in a Gaussain Laser Standing Wave with Different Laser Power

One-dimensional deposition of a neutral chromium atomic beam focused by a near-resonant Gaussian standing- laser field is discussed by using a fourth-order Runge-Kutta type algorithm. The deposition pattern of neutral chromium atoms in a laser standing wave with different laser power is discussed and the simulation result shows that the full width at half maximum （FWHM） of a nanometer stripe is 115nm and the contrast is 2.5：1 with laser power 3.93mW; the FWHM is 0.8nm and the contrast is 27：1 with laser power 16mW, the optimal laser power; but with laser power increasing to 50mW, the nanometer structure forms multi-crests and the quality worsens quickly with increasing laser power.     

Laser cooling with electromagnetically induced transparency: application to trapped samples of ions or neutral atoms

A novel method of ground-state laser cooling of trapped atoms utilizes the absorption profile of a three- (or multi-) level system that is tailored by a quantum interference. With cooling rates comparable to conventional sideband cooling, lower final temperatures may be achieved. The method was experimentally implemented to cool a single Ca⁺ ion to its vibrational ground state. Since a broad band of vibrational frequencies can be cooled simultaneously, the technique will be particularly useful for the cooling of larger ion strings, thereby being of great practical importance for initializing a quantum register based on trapped ions. We also discuss its application to different level schemes and for ground-state cooling of neutral atoms trapped by a far-detuned standing wave laser field. Received: 10 July 2001 / Published online: 23 November 2001