Cold Rb Atoms Research Articles

Deflecting, focusing, and funnelling atoms by near-field light

We describe atom deflection with a slit-type deflector as an elemental technique of precise atom control using near-field light. In the demonstration experiments, cold Rb atoms deflected by repulsive near-field light induced in a 200?nm-wide slit are detected by means of two-step photoionization. Then, we consider a near-field-light lens of atomic de Broglie waves by developing the atom deflector. The feasibility of nanofocusing is shown by numerical analyses with Fourier atom optics. Finally, we describe atom funnels with evanescent light to generate a cold atomic beam required for atom manipulation using nanometric near-field light. The flux intensity of cold Rb atoms outputted from a 240??m outlet is estimated to be 7.5 ? 107?atom?cm?2?s?1 at a blue detuning of 1.2?GHz. In order to increase the flux intensity to 1012?atom?cm?2?s?1, we develop a Si-made funnel with a micron-sized outlet.

Cold atom guidance using a binary spatial light modulator

We have guided cold (85)Rb atoms in a blue-detuned, high-order hollow laser beam generated by a binary spatial light modulator. The binary holograms written to the modulator produce smooth hollow laser beams with steep intensity walls that can be updated with a 1.6 kHz refresh rate. We analyze the guiding laser beams numerically and experimentally, and show that the atoms are exposed to an average intensity that is ~2% of the maximum intensity of the guide at a laser detuning of 1 GHz and 2 mW of optical power.

Practical scheme to realize 2D array of BECs on an atom chip: novel 2D magneto-optical and magnetic lattices

An array of square current-carrying wires is proposed to construct a two-dimensional (2D) array of surface magneto-optical traps and Ioffe magnetic ones for realizing a 2D lattice of Bose-Einstein condensations (BECs) on an atom chip. Our study shows that when a vertical homogeneous bias magnetic field is only used, the wires will form a 2D array of quadrupole magnetic traps, which can be used to construct 2D lattice of surface magneto-optical micro-traps. While another horizontal homogeneous bias field is added simultaneously, the above 2D array of quadrupole micro-traps will be changed as an array of surface Ioffe micro-traps, which can be used to form a 2D magnetic lattice and then realize a 2D array of BECs. The dynamic loading process of cold (87)Rb atoms from each micro-MOT into Ioffe micro-trap is studied by using Monte-Carlo simulations, and our results show that the scheme can be used to realize a natural and effective loading of cold atoms from 2D array of micro-MOTs into 2D array of Ioffe micro-traps, and the loading efficiency can be reach ~ 65%. Moreover, the positions of each BEC (or MOT) in 2D array of magnetic micro-traps can be controlled by adjusting the currents in the wires or by changing the additional vertical bias field.

Conditions for spin squeezing in a cold87Rb ensemble

We study the conditions for generating spin squeezing via a quantum non-demolition measurement in an ensemble of cold87Rb atoms. By considering the interaction of atoms in the 5S1/2(F = 1) ground state with probe light tuned near the D2 transition, we show that, for large detunings, this system is equivalent to a spin-1/2 system when suitable Zeeman substates and quantum operators are used to define a pseudo-spin. The degree of squeezing is derived for the rubidium system in the presence of scattering causing decoherence and loss. We describe how the system can decohere and lose atoms, and predict as much as 75% spin squeezing for atomic densities typical of optical dipole traps.

Nonlinear wave mixing with electromagnetically induced transparency in cold atoms

Electromagnetically induced transparency (EIT) in a four-level atomic system suppresses linear absorption and leads to resonantly enhanced slow-light four-wave mixing at low light intensities. We analyse the backward four-wave mixing in the four-level system under the EIT conditions, derive the four-wave-mixing efficiency and discuss slow-light propagation conditions. We present experimental measurements of resonant four-wave mixing with the backward scheme in cold Rb atoms and compare the experimental results with the theoretical calculations.

A frequency-doubled laser system producing ns pulses for rubidium manipulation

We have constructed a pulsed laser system for the manipulation of cold 87Rb atoms. The system combines optical telecommunications components and frequency doubling to generate light at 780 nm. Using a fast, fibre-coupled intensity modulator, we sliced output from a continuous laser diode into pulses with a length between 1.3 and 6.1 ns and a repetition frequency of 5 MHz. These pulses are amplified using an erbium-doped fibre amplifier, and frequency-doubled in a periodically poled lithium niobate crystal, yielding a peak power up to 12 W. Using the resulting light at 780 nm, we demonstrate Rabi oscillations on the F=2,mF=+2↔F′=3, m′ F=+3-transition of a single 87Rb atom.

Simple and efficient magnetic transport of cold atoms using moving coils for the production of Bose–Einstein condensation

We have developed a simple magnetic transport method for the efficient loading of cold atoms into a magnetic trap. Laser-cooled 87Rb atoms in a magneto-optical trap (MOT) are transferred to a quadrupole magnetic trap and they are then transported as far as 50 cm by moving magnetic trap coils with a low excess heating of atoms. A light induced atom desorption technique helps to reduce the collision loss during the magnetic transport. Using this method, we can load cold 87Rb atoms into a magnetic trap in an ultra high vacuum chamber with high efficiency, and we can produce 87Rb condensate atoms.

QED-modified radiative properties and dynamics of cold atoms moving through an evanescent wave

Measurements of the radiative properties of cold 87Rb atoms close to a dielectric/vacuum interface are reported. This is the first observation of a quantum-electrodynamic (QED) modification of radiative properties in vacuum near a dielectric surface. Evanescent wave (EW) spectroscopy on cold atoms that were dropped on a glass surface was used. An increase of the natural linewidth by up to 25% compared to the free space value was found. This was attributed to QED broadening and level shifts, as well as local Stark shifts near the surface. By varying the characteristic EW length, a position dependence characteristic for QED was observed. The role of transient internal dynamics of the atoms as they move through the strongly inhomogeneous EW was investigated.

Abnormal Phenomenon of ac Stark splitting in Magneto-OpticalTraps

We experimentally study the ac Stark splitting in D2 line of cold87Rb atoms. The frequency span between the Autler–Townesdoublets is obviously larger than that derived from theoreticalcalculation. Two physical effects, which increase the effective Rabifrequency, contribute to the splitting broadening. First, atoms tend todistribute in strong field places of a inhomogeneous red-detuned lightfield. Second, atoms reabsorb scattered light when they are huge innumber and high in density.

Generation of Paired Photons with Controllable Waveforms

We describe experiments and theory showing the generation of counterpropagating paired photons with coherence times of about 50 ns and waveforms that are controllable at a rudimentary level. Using cw lasers, electromagnetically induced transparency and cold 87Rb atoms we generate paired photons into opposing single-mode optical fibers at a rate of approximately 12 000 pairs per second.

Application of photon scanning tunneling microscope to measure optical near field for atom manipulation

Photon scanning tunneling microscope has been employed to measure the three-dimensional evanescent optical field of an atom funnel. A 3.8 neV repulsive optical potential has been estimated by a 300 μ m long probe with a tip radius of curvature of 21 nm. We have estimated limiting conditions for cold Rb atoms to reflect from the atom funnel. A two-dimensional doughnut-shaped optical near field has also been investigated. An aperture fiber probe is used to profile a focussed TEM 01 beam at the minimum beam waist and measure a dark center of about 10 μ m while it is focussed by a converging lens of focal length 8 cm.

Optical Nutation in Cold 85Rb Atoms

We have observed optical nutation in cold 85Rb atoms with a negligible Doppler broadening. The optical nutation of a two-level atom arranged by optical pumping has been studied as a function of detuning frequency and Rabi frequency. The change of the nutation signal caused by magnetic substate degeneracy has also been observed for σ and π excitations. This can be explained by optical nutation beatings from different transition probabilities among magnetic sublevels. Absolute transition probabilities with σ and π transitions and a branching ratio between them have been measured.

A novel array of surface hollow optical micro-traps

In this paper, we propose a new scheme to form an array of surface hollow optical micro-traps for cold atoms (or molecules) by using a phase grating with four phase steps and an array of microlens, study the intensity distribution of 2D array of surface hollow optical micro-traps, and calculate the corresponding optical potential for cold 85Rb atoms, and discuss some potential applications of our hollow micro-trap array in atom and molecule optics. Our study shows that when our grating-lens system is illuminated by YAG laser with a power of 1W, a 2D array of surface hollow optical traps with 104 micro-wells will be generated in an area of 1cm2. Each optical trap has some novel characteristics, such as smaller trapping volume, higher effective intensity and its intensity gradient. The corresponding optical potential for trapped 85Rb atoms can reach 190μK, which is high enough to trap cold atoms or cold molecules, and can be used to realize an all-optical atomic and molecular Bose-Einstein condensations, even to prepare novel optical lattices, and so on.

Resonant four-wave mixing with slow light

Electromagnetically induced transparency in a four-level atomic system suppresses the linear susceptibility and enhances the nonlinear susceptibilities, which leads to the resonantly enhanced slow-light four-wave mixing at low light intensities. We report an experimental observation of such resonant four-wave mixing in cold Rb atoms.

Observation of cold atom output from an evanescent-light funnel

We report the demonstration of an atom funnel composed of evanescent light. The flux intensity of cold Rb atoms output from a 240μm exit hole was 7×107atom∕cm2s at a blue detuning of 1.2GHz. Sisyphus cooling doubled the output efficiency. The estimated flux intensity was 1012atom∕cm2s when the exit-hole diameter was 110μm.

Microwave spectroscopy of cold rubidium atoms

The effect of microwave radiation on the resonance fluorescence of a cloud of cold 85Rb atoms in a magnetooptical trap is studied. The radiation frequency was tuned near the hyperfine splitting frequency of rubidium atoms in the 5S ground state. The microwave field induced magnetic dipole transitions between the magnetic sublevels of the 5S (F=2) and 5S (F=3) states, resulting in a change in the fluorescence signal. The resonance fluorescence spectra were recorded by tuning the microwave radiation frequency. The observed spectra were found to be substantially dependent on the transition under study and the frequency of a repump laser used in the cooling scheme.

Electromagnetically induced transparency in multi-level cascade scheme of cold rubidium atoms

We report an experimental investigation of electromagnetically induced transparency in a multi-level cascade system of cold 85Rb atoms. The absorption spectral profiles of the probe light and their dependence on the intensity of the coupling laser were investigated. The experimental measurements agree with the theoretical calculations.

Superluminal and slow light propagation in cold atoms

The group velocity of a light pulse propagating through a four-level system exhibiting electromagnetically induced transparency can be manipulated by a pump laser. The pump laser induces the large optical nonlinearities with steep normal or anomalous dispersion. We present experimental measurements that demonstrate both slow and superluminal light propagation in cold Rb atoms.

Generation of One-Dimensional Array of Focused Hollow-BeamPipes and Its Surface Microscopic Waveguide for Cold Atoms or Molecules

We propose a new scheme to guide cold atoms (or molecules) by usinga one-dimensional (1D) array of focused hollow-beam pipes generated bythe combination of a binary phase grating and a 1D array ofmicro-cylindrical lenses on the substrate surface. We also calculatethe intensity distribution of the focused hollow-beam pipe array and itsoptical potential for 85Rb atoms. The result shows that when theblue detuning of the incident beam and its intensity are 10 GHz and7.0×103 W/m2 respectively, the horizontal dark spot sizeof each focused hollow-beam pipe and the efficient optical potentialare 4.4 μm and ~0.23 mK, which is high enough to guide cold85Rb atoms (~20 μK) from a standard optical molasses andthen to realize the 1D array of surface atomic waveguides on an atom chip.

Nonlinear magneto-optical effects in cold atoms of 87 Rb

With laser-cooled cold 87Rb atoms as a magneto-optical medium, a weak right circularly polarized probe field and frequency modulation technique are used to detect the magnetic distribution of the quadrupole field. A two-peak dispersion-like signal other than that of the usual nonlinear magneto-optical effect mentioned in other papers is obtained.