Standard Magneto-optical Trap Research Articles

Microfabricated evanescent-light funnel with high-intensity cold atom flux

We process a silicon-on-insulator substrate into a funnel with a 25-μm-side square-shaped outlet by photolithography and anisotropic chemical etching. The funnel is utilized to form a cold atomic beam by means of reflection and cooling on repulsive evanescent light. Monte Carlo simulations show that the flux intensity of emitted cold Rb atoms reaches 10 12 cm −2 s −1. The mean horizontal velocity is estimated to be below 10 cm/s, while the mean vertical velocity decreases in proportion to the outlet side. The evanescent-light funnel can be developed to concentrate 80% of Rb atoms falling from a standard magneto-optical trap.

Cold Atom Trap with Zero Residual Magnetic Field: The ac Magneto-Optical Trap

A novel atom trap is described using alternating current to generate the magnetic B field, together with high speed polarization switching of the damping laser field. This combination produces a trap as effective as a standard magneto-optical trap (MOT), with the advantage that the average B field is zero. No net current is hence induced in surrounding conductive elements, and the B field produced by the ac MOT is found to switch off >300 times faster than a conventional MOT. New experiments can hence be performed, including charged particle probing or detection of the cold target ensemble.

Realization of a single-beam mini magneto-optical trap: A candidate for compact CPT cold atom-clocks

We have demonstrated the experimental realization of a single-beam mini magneto-optical trap of 87Rb atoms, originally designed for a cold atom-clock with coherent population trapping (CPT). Only one beam is used as cooling, trapping and repumping beams rather than the three pairs of orthogonal beams of the standard magneto-optical trap. The core optics, which consists of a modified pyramidal funnel type mirror, a quarter-wave plate and a retroreflect mirror, is installed inside a mini titanium cubic chamber. The vacuum system, rubidium source, magnetic field coils and beam expander are designed in a compact geometry. As many as 1.1 × 10 7 rubidium atoms are cooled and trapped, and thus the mini trap is ready for the implementation of a novel compact coherent population trapping cold atom-clock.

Measurement of the3s3p P31lifetime in magnesium using a magneto-optical trap

We demonstrate an accurate method for measuring the lifetime of long-lived metastable magnetic states using a magneto-optical trap (MOT). Through optical pumping, the metastable $(3s3p)\text{ }{^{3}P}_{1}$ level is populated in a standard MOT. During the optical pumping process, a fraction of the population is captured in the magnetic quadrupole field of the MOT. When the metastable atoms decay to the $(3{s}^{2})\text{ }{^{1}S}_{0}$ ground state they are recaptured into the MOT. In this system no alternative cascading transition is possible. The lifetime of the metastable level is measured directly as an exponential load time of the MOT. We have experimentally tested our method by measuring the lifetime of the $(3s3p)\text{ }{^{3}P}_{1}$ of $^{24}\text{M}\text{g}$. This lifetime has been measured numerous times previously, but with quite different results. Using our method we find the $(3s3p)\text{ }{^{3}P}_{1}$ lifetime to be $(4.4\ifmmode\pm\else\textpm\fi{}0.2)\text{ }\text{ms}$. Theoretical values point toward a lower value for the lifetime.

Bose-Einstein condensation in 87Rb: characterization of the Brazilian experiment

We describe the experimental apparatus and the methods to achieve Bose-Einstein condensation in 87Rb atoms. Atoms are first laser cooled in a standard double magneto-optical trap setup and then transferred into a QUIC trap. The system is brought to quantum degeneracy selectively removing the hottest atoms from the trap by radio-frequency radiation. We also present the main theoretical aspects of the Bose-Einstein condensation phenomena in atomic gases.

2D dark optical surface lattice with an efficient intensity-gradient cooling of atoms by evanescent wave interference

We propose a novel scheme to form a 2D dark optical surface lattice (DOSL) for cold atoms on the surface of the dense flint glass by using two sets of blue-detuned evanescent wave interference fields and a blue-detuned evanescent wave field. In the 2D DOSL, cold atoms will be trapped in the vicinity of minimum intensity and suffered the minimal light shift as well as the lowest coherence loss. The total potential and trap-depth of the individual optical micro-trap in the 2D DOSL are high enough to trap cold atoms (T=120μK) released from the standard magneto-optical trap (MOT), and atoms trapped in the 2D DOSL can be cooled to several μK with the efficient intensity-gradient Sisyphus cooling. The lattice constant of the DOSL can be controllable by changing the incident angles of lights.

2D array of surface optical micro-traps by evanescent wave interference

We propose a novel scheme to form a 2D surface array of optical micro-traps of cold atoms by using two sets of far red-detuned evanescent wave interference and a blue-detuned evanescent wave. The optical potentials of the 2D surface array of optical micro-traps are high enough to trap cold atoms released from the standard magneto-optical trap，and 87Rb atoms trapped in the array of optical micro-traps can be cooled to 2.56μK with efficient intensity-gradient Sisyphus cooling. Our study shows that the proposed 2D surface array of optical micro-traps can be used in atomic physics，atomic optics, quantum optics and so on.

High Resolution Spectroscopy of Cold, Trapped Atoms

1. IntroductionCold atoms in atomic traps are attractive samples for many important ex-periments. One of few available methods for their diagnostics is laser spectroscopy.In this paper we present typical spectra obtained by nonlinear Raman pump-probespectroscopy and discuss their main features and applications.In our experiment we use a standard vapor-loaded magneto-optical trap(MOT). In order to perform high resolution Raman spectroscopy one of the lasersserves as the master for injection seeding into the trapping, pump and probe lasers.Their frequency shifts are controlled by acousto-optic modulators (AOMs). Theprobe beam enters the cloud of cold atoms making a small angle

Observation of nonlinear optical recoil-induced resonances in a dark magneto-optical trap

Nonlinear optical recoil-induced resonances have been observed in a gas of cold rubidium atoms trapped in a dark magneto-optical trap. These resonances are used to measure the temperature and velocity distribution of the cold atoms. The velocity distribution of the atoms in the dark magneto-optical trap has an excessive amount of fast atoms as compared to the Maxwell distribution and to the distribution in a standard magneto-optical trap.

Efficient intensity-gradient cooling of atoms in a weak standing-wave hollow-beam trap

We propose a trap scheme for cold alkali-metal atoms with an efficient intensity-gradient induced Sisyphus cooling in a weak standing-wave hollow-beam gravito-optical trap, which is composed of the interference of two well collimated, counterpropagating doughnut hollow beams with an intensity difference and a plug beam. We calculate the intensity distribution of the weak standing-wave hollow-beam field and its intensity gradient one, and find that such an optical dipole trap with an extremely high intensity gradient is desirable to realize an efficient intensity-gradient cooling for alkali-metal atoms in the trap. We also calculate the optical potentials, instantaneous dipole forces and spontaneous emission rates for a three-level dressed atom and study the dynamic process of intensity-gradient cooling of $^{87}\mathrm{Rb}$ atoms in the weak standing-wave hollow-beam trap by Monte Carlo simulations. Our study shows that the minimum optical potential at each node in our dipole trap is high enough to trap almost all cold atoms with a temperature of $120\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ released from a standard magneto-optical trap, and an ultracold $^{87}\mathrm{Rb}$ atomic sample with a temperature of $\ensuremath{\sim}0.73\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ can be obtained in the trap. Starting from this stage, an all-optical Bose-Einstein condensation (BEC) could be realized by using the optical-potential evaporative cooling.

A Novel Gravito-Optical Surface Trap for Neutral Atoms

We propose a novel gravito-optical surface trap (GOST) for neutralatoms based on one-dimensional intensity gradient cooling. The surfaceoptical trap is composed of a blue-detuned reduced semi-Gaussian laserbeam (SGB), a far-blue-detuned dark hollow beam and the gravity field.The SGB is produced by the diffraction of a collimated Gaussian laserbeam passing through the straight edge of a semi-infinite opaque plateand then is reduced by an imaging lens. We calculate the intensitydistribution of the reduced SGB, and study the dynamic process of theSGB intensity-gradient induced Sisyphus cooling for 87Rb atomsby using Monte Carlo simulations. Our study shows that the proposedGOST can be used not only to trap cold atoms loaded from a standardmagneto-optical trap, but also to cool the trapped atoms to anequilibrium temperature of 3.47 μK from ~120 μK, even torealize an all-optical two-dimensional Bose–Einstein condensation byusing optical-potential evaporative cooling.

Atom chip based fast production of Bose–Einstein condensate

We have developed a simple method for the fast and efficient production of a Bose–Einstein condensate (BEC) on an atom chip. By using a standard six-beam magneto-optical trap and light-induced atom desorption for loading, 3×10787Rb atoms are collected within 1 s and loaded into a small-volume magnetic potential of the chip with high efficiency. With this method, a BEC of 3×103 atoms is realized within a total time of 3 s. We can realize a condensate of up to 2×104 atoms by reducing three-body collisions. The present system can be used as a fast and high-flux coherent matter-wave source for an atom interferometer.

Guiding and cooling of atoms in an interference field composed of two hollow beams

We propose a new scheme to guide and cool three-level alkali-metal atoms in a blue-detuned interference field composed of two counter-propagating doughnut hollow beams, and analyze the intensity distribution of the interference field of the two hollow beams and its intensity gradient one. Our study shows that the high intensity gradient of the interference field is desirable to realize intensity-gradient cooling for the guided atoms, and the minimum optical potential at the nodes of the interference field is high enough to guide almost all atoms released from a standard magneto-optical trap. We also perform Monte-Carlo simulations for dynamic process of the intensity-gradient cooling, and show that an (87)Rb atomic sample with a temperature of 120 muK can be directly cooled to a final equilibrium temperature of 4.71 muK in our guiding scheme.

A Novel Atomic Guiding Using a Blue-Detuned TE01 Mode inHollow Metallic Waveguides

We propose a novel scheme to guide cold atoms using a blue-detunedTE01 doughnut mode in a hollow metallic waveguide, calculate theelectromagnetic field distribution of the TE01 mode in thehollow metallic waveguide, and compare the attenuation characters of theEH11 and TE01 mode in the hollow metallic waveguide. Wealso calculate the optical potential of the TE01 doughnut modefor two-level 85Rb atoms and estimate the photon scatteringrate. It is found that when the detuning δ = 300 GHz, the photonscattering induced heating can be neglected, and the optical potential(Umax≈570 mK) of the TE01 mode is high enough toload cold atoms (120 μK) from a standard magneto-optical trap and toguide them in the hollow metallic waveguide, which is a desirablescheme to realize a computer-controlled atom lithography with anarbitrary pattern.

Atomic (or molecular) guiding using a blue-detuned doughnut mode in a hollow metallic waveguide

We propose a new scheme to guide cold atoms (or molecules) using a blue-detuned TE(01) doughnut mode in a hollow metallic waveguide (HMW), and analyze the electromagnetic field distributions of various modes in the HMW. We calculate the optical potentials of the TE(01) doughnut mode for three-level atoms using dressed-atom approach, and find that the optical potential of the TE(01) mode is high enough to guide cold atoms released from a standard magneto-optical trap. Our study shows that when the input laser power is 0.5W and its detuning is 3GHz, the guiding efficiency of cold atoms in the straight HMW with a hollow radius of 15 microm can reach 98%, and this guiding efficiency will be almost unchanged with the change of curvature radius R of the bent HMW as R > 2cm, which is a desirable scheme to do some atom-optics experiments or realize a computer-controlled atom lithography with an arbitrary pattern. We also analyze the losses of the guided atoms in the HMW due to the spontaneous emission and background thermal collisions and briefly discuss some potential applications of our guiding scheme in atom and molecule optics.

A simple laser cooling and trapping apparatus for undergraduate laboratories

We present detailed instructions for the construction of a pyramidal-style laser cooling and trapping apparatus. This scheme requires only a single beam, rather than the three pairs of orthogonal beams of the standard magneto-optical trap, which greatly simplifies the geometry and substantially reduces the cost. The trap is based largely on low-cost commercially available items and is simple to construct. It is remarkably insensitive to alignment and reliable to operate. Using a single laser beam with an intensity of 1.3 mW/cm2 we cool and trap more than 4 million rubidium atoms.

Doppler cooling and trapping on forbidden transitions.

Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of (40)Ca atoms has been cooled and trapped to a temperature as low as 6 microK by operating a magnetooptical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method, more than 10% of precooled atoms from a standard magnetooptical trap have been transferred to the ultracold trap. Monte Carlo simulations of the cooling process are in good agreement with the experiments.

A continuous cold atomic beam from a magneto-optical trap

We have developed and characterized a new method to produce a continuous beam of cold atoms from a standard vapour-cell magneto-optical trap (MOT). The experimental apparatus is very simple. Using a single laser beam it is possible to hollow out in the source MOT a direction of unbalanced radiation pressure along which cold atoms can be accelerated out of the trap. The transverse cooling process that takes place during the extraction reduces the beam divergence. The atomic beam is used to load a magneto-optical trap operating in an ultra-high vacuum environment. At a vapour pressure of 10-8mbar in the loading cell, we have produced a continuous flux of 7×107atoms/s at the recapture cell with a mean velocity of 14 m/s. A comparison of this method with a pulsed transfer scheme is presented.

A proposal for ac magnetic guide and trap of cold atoms

We propose a novel ac electro-magnetic wave guide for cold neutral atoms in an Ioffe tube, which is based on the interaction of a magnetic dipole moment of a guided atom with both an ac quadrupole magnetic field in the transverse direction and a dc-bias magnetic field along the guiding axis. The time-averaged magnetic potential and force for the guided atoms in the magnetic guiding tube are calculated. The results show that the potential is high enough to collect and guide nearly all cold atoms from a standard magneto-optical trap with a temperature of ∼120 μK. We also estimate the atomic losses from collisions with background thermal atoms, quantum tunneling and spin-flip transitions in the guiding process. Our study indicates that a cold and dense atomic beam with a guiding efficiency of ∼92% and a beam intensity of about 10 11 atoms/cm 2/s can be output from the magnetic guide tube, and the guiding scheme proposed here could be used to manipulate spin-polarized cold atoms.

Standing light fields for cold atoms with intrinsically stable and variable time phases

We present a novel method to realise a standing light field with a stable configuration in two or three dimensions. A single standing wave formed by two counterpropagating beams is folded and brought into intersection with itself. The values of the relative timephases are stable, a priori known, and can be altered arbitrarily by means of retardation plates. The polarisation configurations of three orthogonal standing waves include the standard magnetooptical trap and a novel three-dimensional pure polarisation lattice which we have investigated in a first spectroscopic measurement, providing strong evidence for atomic localisation in both cases.