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Chinese Physics Letters

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

Yang Liu, Jinghui Wu, Bao‐Sen Shi, Guang‐Can Guo

Published Feb 1, 2012• 31 citations
Publisher

Abstract

We build up a novel setup of a two-dimensional (2D) 85 Rb magneto-optical trap (MOT) with a high optical depth (OD) of 38. Such a MOT trap of 85 Rb 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 γ 21 = 0.008γ 31 , which is much less than that in a normal MOT. The total number of atoms in this MOT was measured to be 9.1 × 10 8 .

DOI
10.1088/0256-307x/29/2/024205

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We build up a novel setup of a two-dimensional (2D) 85 Rb magneto-optical trap (MOT) with a high optical depth (OD) of 38. Such a MOT trap of 85 Rb 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 γ 21 = 0.008γ 31 , which is much less than that in a normal MOT. The total number of atoms in this MOT was measured to be 9.1 × 10 8 .
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.
We have constructed in our laboratory two rectangular shaped current carrying coils in accordance with the parameters used in our design so that they can be put in use in the Two Dimensional Magneto Optical Trap (2D-MOT)to obtain very high value of Optical Depth(OD). The dimensions of the coils are 8cm x 10cm. When put in anti-Helmholtz configuration as required in a 2D-MOT, these coils generate magnetic field such that it becomes zero along a line bisecting the space between the two coils. The magnetic field gradient near the zero magnetic field line is measured to be 3.33 Gauss/cm when the current passing through the coils is 3.5A. We have also made measurements at other values of current and found, as expected, this gradient increases with current. These results match nicely with the estimated values and hence a significant step forward towards the experimental realization of the design proposed by us.
We describe a three-dimensional (3D) magneto-optical trap (MOT) capable of simultaneously capturing 85Rb and 133Cs atoms. Unlike conventional setups, our system utilizes two separate laser systems that are combined before entering the vacuum chamber, enabling the simultaneous trapping of two different atomic species. Additionally, in our 3D MOT configuration, two (of three) pairs of laser beams are not orthogonal to the chamber surfaces but are aligned at a 45° angle. With a total trapping laser power of 8 mW and repump laser power of 4 mW for Rb atoms, and a total trapping laser power of 7.5 mW and repump laser power of 1.5 mW for Cs atoms, we achieve optical depths (OD) of 3.71 for Rb and 3.45 for Cs, demonstrating efficient trapping for both species. Our 3D MOT setup allows full horizontal optical access to the trapped atomic ensembles without spatial interference from the trapping or repump laser beams. Moreover, the red detuning for trapping both atomic species is smaller than in traditional configurations. This system offers a versatile platform for exploring complex phenomena in ultracold atom physics, such as Rydberg molecule formation and interspecies interactions.
We present an experimental study to achieve ultrahigh optical depths for cold atomic media with a two-dimensional magneto-optical trap (MOT) of cesium. By combining large atom number, a temporally dark and compressed MOT, and Zeeman-state optical pumping, we achieve an optical depth of up to 1306 for the open transition of the cesium D1{D}_{1}D1​ line. Our work demonstrates that it is feasible to push the optical depth up to the 1000 level with a convenient MOT setup. This development paves the way to many important proposals in quantum optics and many-body physics.
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, m F = −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.
In this paper, we propose a novel technique for slow light experiments using electromagnetically induced transparency using a two-dimensional magneto optical trap (2D-MOT). A compact 2D-MOT design efficient for quantum memory applications with adjustable optical depth (OD) is proposed. We estimated the OD for our 2D-MOT setup and found that light group velocities as low as 1.4 m/s can be attained. Our design for 2D-MOT allows precise control and optimization of the OD such that high storage efficiencies could also be achieved. With our design, it is possible to obtain a delay bandwidth product of 163, which is very high in comparison to previously obtained values.