Two-dimensional Magneto-optical Trap Research Articles

A two-dimensional magneto-optical trap for a cesium fountain clock

To study the relationship of atomic beam flow with cooling intensity, laser detuning, and magnetic field gradient, the numerical simulation is performed and a two-dimensional magneto-optical trap setup is built. A low-velocity atomic beam flow is generated with a total flux of 2.1 109/s. Theoretical analysis and experimental results are in good consistence. Optimal detuning and magnetic field gradient can produce the largest atomic beam flow.

High-performance experimental apparatus for large atom number 87Rb Bose-Einstein condensates

We describe our high-performance experimental apparatus for producing large atom number 87Rb Bose-Einstein condensates by using a double magneto-optical trap (MOT) system that consists of a two-dimensional MOT (2D MOT) and a three-dimensional MOT (3D MOT). As an atomic beam source for loading the 3D MOT, we use a unique 2D MOT system with two-color pushing beams, which increase the loading rate and the total number of atoms in the 3D MOT, compared to a pure 2D MOT by a factor of 20. After MOT compression and polarization gradient cooling, atoms are optically pumped into a magnetically trappable hyperfine state |F = 1, mF = −1〉 to be loaded into a quadrupole-Ioffe-configuration (QUIC) trap. We enhance this optical pumping process by up to 300% by using two laser beams. After rf evaporative cooling, a Bose-Einstein condensate (BEC) with more than 2 × 107 atoms is achieved.

A compact high-efficiency cold atom beam source

We report on an efficient and compact high-flux Cs atom beam source based on a retro-reflected two-dimensional magneto-optical trap (2D MOT). We realize an effective pushing field component by tilting the 2D MOT collimators towards a separate three-dimensional magneto-optical trap (3D MOT) in ultra-high vacuum. This technique significantly improved 3D MOT loading rates to greater than $8 \times 10^9$ atoms/s using only 20 mW of total laser power for the source. When operating below saturation, we achieve a maximum efficiency of $6.2 \times 10^{11}$ atoms/s/W.

Versatile cold atom target apparatus

We report on a compact and transportable apparatus that consists of a cold atomic target at the center of a high resolution recoil ion momentum spectrometer. Cold rubidium atoms serve as a target which can be operated in three different modes: in continuous mode, consisting of a cold atom beam generated by a two-dimensional magneto-optical trap, in normal mode in which the atoms from the beam are trapped in a three-dimensional magneto-optical trap (3D MOT), and in high density mode in which the 3D MOT is operated in dark spontaneous optical trap configuration. The targets are characterized using photoionization.

A dark-line two-dimensional magneto-optical trap of 85Rb atoms with high optical depth

We describe the apparatus of a dark-line two-dimensional (2D) magneto-optical trap (MOT) of (85)Rb cold atoms with high optical depth (OD). Different from the conventional configuration, two (of three) pairs of trapping laser beams in our 2D MOT setup do not follow the symmetry axes of the quadrupole magnetic field: they are aligned with 45° angles to the longitudinal axis. Two orthogonal repumping laser beams have a dark-line volume in the longitudinal axis at their cross over. With a total trapping laser power of 40 mW and repumping laser power of 18 mW, we obtain an atomic OD up to 160 in an electromagnetically induced transparency (EIT) scheme, which corresponds to an atomic-density-length product NL = 2.05 × 10(15) m(-2). In a closed two-state system, the OD can become as large as more than 600. Our 2D MOT configuration allows full optical access of the atoms in its longitudinal direction without interfering with the trapping and repumping laser beams spatially. Moreover, the zero magnetic field along the longitudinal axis allows the cold atoms maintain a long ground-state coherence time without switching off the MOT magnetic field, which makes it possible to operate the MOT at a high repetition rate and a high duty cycle. Our 2D MOT is ideal for atomic-ensemble-based quantum optics applications, such as EIT, entangled photon pair generation, optical quantum memory, and quantum information processing.

Cold atomic beam from a two-dimensional magneto-optical trap with two-color pushing laser beams

We present an intense source of cold rubidium atoms from a two-dimensional magneto-optical trap (2D MOT) with a two-color pushing laser that generates an adjustable mean velocity ranging from 20 to 45m/s. The dependence of the flux and velocity distribution on the pushing beam parameters such as laser detuning and laser power was investigated in detail. We obtained a flux Φ=4.5×1010atoms/s with the total laser power of 60mW at a vapor pressure of 1.2×10−7torr. By adding a red-detuned pushing beam (Δ−=−4.5Γ) into a blue-detuned one (Δ+=+4.5Γ) the flux was increased by more than a factor of 2. Furthermore this modified 2D MOT system improved 3D MOT loading rate to greater than 3×1010atoms/s keeping the background pressure below 10−11torr in the ultra-high-vacuum chamber.

Realization of a Two-Dimensional Magneto-optical Trap with a High Optical Depth

We build up a novel setup of a two-dimensional (2D) 85Rb magneto-optical trap (MOT) with a high optical depth (OD) of 38. Such a MOT trap of 85Rb has several advantages as compared to the normal three-dimensional ellipsoidal MOT. Firstly, it will greatly enhance atom-photon interaction due to the large OD. Then, the dephasing caused by the magnetic gradient will be decreased in the long axis of the 2D MOT, which we want to avoid from in the experiments. The metastable ground level dephasing rate was γ21 = 0.008γ31, which is much less than that in a normal MOT. The total number of atoms in this MOT was measured to be 9.1 × 108.

A Simplified Cold Atom Source for 3-D MOT Loading

A simplified two-dimensional (2-D) magneto-optical trap (MOT) for loading atoms into a 3-D MOT is realized. Instead of utilizing multiple wave plates and beam splitters to cover a large cooling region, we deploy cooling beams with elliptical cross-section profiles to achieve a comparable cooling volume. This simplification reduces the cost and difficulty of alignment. The 3-D MOT achieves a loading rate of 2 × 108 atoms per second via this simplified 2-D MOT. Correlation between the loading rate and parameters of optical system is also determined.

Hexapole-compensated magneto-optical trap on a mesoscopic atom chip

Magneto-optical traps on atom chips are usually restricted to small atomic samples due to a limited capture volume caused primarily by distorted field configurations. Here we present a magneto-optical trap based on a millimeter-sized wire structure which generates a magnetic field with minimized distortions. Together with the loading from a high-flux two-dimensional magneto-optical trap, we achieve a loading rate of $8.4\ifmmode\times\else\texttimes\fi{}{10}^{10}$ atoms/s and maximum number of $8.7\ifmmode\times\else\texttimes\fi{}{10}^{9}$ captured atoms. The wire structure is placed outside of the vacuum to enable a further adaptation to new scientific objectives. Since all magnetic fields are applied locally without the need for external bias fields, the presented setup will facilitate parallel generation of Bose-Einstein condensates on a conveyor belt with a cycle rate above $1$ Hz.

Subnatural Linewidth Biphotons with Controllable Temporal Length

This Letter describes the generation of biphotons with a temporal length that can be varied over the range of 50-900 ns, with an estimated subnatural linewidth as small as 0.75 MHz. We make use of electromagnetically induced transparency and slow light in a two-dimensional magneto-optical trap with an optical depth as high as 62. We report a sharp leading edge spike that is a Sommerfeld-Brillouin precursor, as observed at the biphoton level.

Realization of an intense cold Rb atomic beam based on a two-dimensional magneto-optical trap: Experiments and comparison with simulations

We discuss the implementation and characterization of the source of a slow, intense, and collimated beam of rubidium atoms. The cold atomic beam is produced by two-dimensional magneto-optical trapping in directions transverse to the atomic beam axis and unbalanced Doppler cooling in the axial direction. The vacuum design allows use of relatively low laser power and a considerably simplified assembly. The atomic beam has a high flux of about $2\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}∕\mathrm{s}$ at a total cooling laser power of $55\phantom{\rule{0.3em}{0ex}}\mathrm{mW}$. It has a narrow longitudinal velocity distribution with mean velocity $15\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$ with full width at half maximum $3.5\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$ and has a low divergence of $26\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$. The high flux enables ultrafast loading of about ${10}^{10}$ atoms into a three-dimensional (3D) magneto-optical trap within 500 ms. The variation of the atomic beam flux was studied as a function of the rubidium vapor pressure, cooling laser power, transverse cooling laser beam length, detuning of the cooling laser, and relative intensities of the cooling beams along the atomic beam axis. We also discuss a detailed comparison of our measurements of the cold atomic beam with a 3D numerical simulation.

A novel simplified two-dimensional magneto-optical trap as an intense source of slow cesium atoms

We describe the design and performance of a slow atom source based on a 2D magneto-optical trap (MOT) that uses an innovative simple optical configuration. Metal-coated retro-reflecting prisms replace mirrors and quarter-wave plates so the optical power of the cooling laser beam is recycled. This source has been characterised for three different configurations: with and without transverse magnetic field gradient, and with a pusher beam to obtain a 2D + -MOT. The longitudinal velocity is of the order of 25 m·s −1 , with a transverse velocity spread ≤1 m·s −1 , while the typical atomic flux density obtained is up to 1.3×10 14 at ·s −1 ·m −2 for a cesium vapour pressure of ~4×10 −8 mbar in the source. We use this slow atom beam, instead of cesium vapour, to load a 3D moving optical molasses that feeds a continuous cold atom fountain. We obtain a gain of a factor ~20 in the atomic flux launched by the fountain.

Multistage two-dimensional magneto-optical trap as a compact cold atom beam source

A compact cold atom beam source based on a multistage two-dimensional magneto-optical trap (MOT) has been demonstrated and characterized. The multiple-stage design greatly reduces the overall size of the source apparatus while providing a high flux of atoms. The cold atom beam was used to load a separate MOT in ultrahigh vacuum, and we obtained an actual trap loading rate of 1.5 x 109 atoms/s while using only 20 mW of total laser power for the source. The entire source apparatus, including optics, can fit into a 4 cm x 4 cm x 13 cm volume.

Intense slow beams of bosonic potassium isotopes

We report on an experimental realization of a two-dimensional magneto-optical trap (2D-MOT) that allows the generation of cold atomic beams of $^{39}\mathrm{K}$ and $^{41}\mathrm{K}$ bosonic potassium isotopes. The high measured fluxes up to $1.0\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}∕\mathrm{s}$ and low atomic velocities around $33\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$ are well suited for a fast and reliable three-dimensional magneto-optical trap loading, a basilar feature for new generation experiments on Bose-Einstein condensation of dilute atomic samples. We also present a simple multilevel theoretical model for the calculation of the light-induced force acting on an atom moving in a MOT. The model gives a good agreement between predicted and measured flux and velocity values for our 2D-MOT.

Focusing of an atomic beam by a two-dimensional magneto-optical trap

A method for focusing neutral atoms based on the light-pressure force in a nonuniform magnetic field is proposed and analyzed. Its particular scheme is realized by means of a two-dimensional magneto-optical trap using a thermal beam of Rb atoms. A feature of this focusing method is the linear dependence of the focal length on the longitudinal velocity of atoms in contrast to the quadratic dependence in the known methods of focusing material-particle beams. The minimum size of the waist of the focused atomic beam is equal to 270 µm. Owing to focusing by means of the two-dimensional magneto-optical trap, the velocity monochromatization of a thermal atomic beam is realized: the width of the distribution of the longitudinal atomic velocities in the beam is reduced from 350 to 60 m/s.

Bidirectional propagation of cold atoms in a “stadium”-shaped magnetic guide

We demonstrate the bidirectional propagation of more than ${10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}$ ${(}^{87}\mathrm{Rb})$ around a ``stadium''-shaped magnetic ring that encloses an area of $10.9\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}$, with a flux density exceeding ${10}^{11}\phantom{\rule{0.3em}{0ex}}\text{atom}\phantom{\rule{0.2em}{0ex}}{\text{s}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. Atoms are loaded into the guide from a two-dimensional (and higher) magneto-optical trap at one side of the ``stadium.'' An optical standing wave pulse is applied to increase the propagation velocity of atoms along the waveguide. The atom sample fills the entire ring in $200\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ when counterpropagating atom sections of the original atom cloud recombine at their initial positions after a full revolution.

A Source of Cold Atoms for a Continuously Loaded Magnetic Guide

We present an intense source of 87Rb atoms that has been set up to produce a continuous, slow and cold beam in a magnetic guide. It consists of a two-dimensional magneto-optical trap whose cooling laser power is provided by a master-oscillator tapered-amplifier system. This trap produces an atomic beam with a flux of over 1010 atoms/s and a mean velocity of 40 m/s. The beam is recaptured by a second trap whose purpose consists in reducing the beam's velocity, in further cooling the atoms and injecting them into the magnetic guide. The article focusses on the first stage of the process described above.

Intense source of cold Rb atoms from a pure two-dimensional magneto-optical trap

We present a two-dimensional (2D) magneto-optical trap (MOT) setup for the production of a continuous collimated beam of cold ${}^{87}\mathrm{Rb}$ atoms out of a vapor cell. The underlying physics is purely two-dimensional cooling and trapping, which allows for a high flux of up to $6\ifmmode\times\else\texttimes\fi{}{10}^{10}$ atoms/s and a small divergence of the resulting beam. We analyze the velocity distribution of the 2D MOT. The longitudinal velocity distribution of the atomic beam shows a broad feature (full width at half maximum $\ensuremath{\simeq}75 \mathrm{m}/\mathrm{s}),$ centered around 50 m/s. The dependence of the flux on laser intensity, on geometry of the trapping volume, and on pressure in the vapor cell was investigated in detail. The influence of the geometry of the 2D MOT on the mean velocity of the cold beam has been studied. We present a simple model for the velocity distribution of the flux based on rate equations describing the general features of our source.

Bright, slow, and continuous beam of laser-cooled cesium atoms

By the moving molasses technique we have extracted laser-cooled cesium atoms in a continuous way directly from an optical molasses. The mean launching velocity is precisely tunable from 1 to 12 m/s. The atomic beam has a flux of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{8} \mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}/\mathrm{s}$ at 7 m/s and a longitudinal temperature of $70 \ensuremath{\mu}\mathrm{K},$ which represents the highest flux and lowest velocity spread obtained so far in a continuous beam of cold atoms. These features makes it well suited for atomic fountains. The atomic flux can be slightly increased in a two-dimensional magneto-optical trap operation $(+40%).$ A simple model accounts for the observed dependence of the flux with the magnetic-field gradient.

Two-dimensional magneto-optical trap as a source of slow atoms

We experimentally study the use of two-dimensional magneto-optical trapping (2D-MOT) for the generation of slow beams of cold atoms out of a vapor cell. A particularly high flux of $9\ifmmode\times\else\texttimes\fi{}{10}^{9}$ rubidium atoms/s at a mean velocity of 8 m/s is obtained using a combination of magneto-optical trapping in two dimensions and Doppler cooling in the third dimension $({2\mathrm{D}}^{+}\ensuremath{-}\mathrm{MOT}).$ The resulting width of the velocity distribution is 3.3 m/s [full width at half maximum (FWHM)] with a beam divergence of 43 mrad (FWHM). We investigate the total flux as a function of vapor cell pressure and determine the velocity distribution of our slow atom sources. For comparison, we also realized a low-velocity intense source (LVIS), first reported by Lu et al. [Phys. Rev. Lett. 77, 3331 (1996)]. We find that the ${2\mathrm{D}}^{+}\ensuremath{-}\mathrm{MOT}$ yields a significantly higher flux than the LVIS, even when used with an order of magnitude less laser power.