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Journal of the Optical Society of America B

Experimental demonstration of controllable double magneto-optical traps on an atom chip

Hui Yan, Yang Guo-Qing, Tao Shi, Jin Wang, Mingsheng Zhan

Published Sep 16, 2008• 2 citations
Publisher

Abstract

We demonstrate controllable double magneto-optical traps (DMOTs) on an atom chip: At first, DMOTs, which trap atoms directly from the background rubidium vapor in an ultrahigh-vacuum environment, are realized on an atom chip simultaneously. The double quadrupole magnetic fields are produced by two separate U-shaped microwires on the atom chip, combined with a bias magnetic field. Then, we determine the best parameters for a U-shaped magneto-optical trap (UMOT) through a detailed comparison of the capture ability at different currents and the bias magnetic field between two different geometric sizes of UMOT. Finally, we demonstrate the mixing and splitting of the DMOTs on the atom chip with the help of an extra pair of anti-Helmholtz coils.

DOI
10.1364/josab.25.001667

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We demonstrate controllable double magneto-optical traps (DMOTs) on an atom chip: At first, DMOTs, which trap atoms directly from the background rubidium vapor in an ultrahigh-vacuum environment, are realized on an atom chip simultaneously. The double quadrupole magnetic fields are produced by two separate U-shaped microwires on the atom chip, combined with a bias magnetic field. Then, we determine the best parameters for a U-shaped magneto-optical trap (UMOT) through a detailed comparison of the capture ability at different currents and the bias magnetic field between two different geometric sizes of UMOT. Finally, we demonstrate the mixing and splitting of the DMOTs on the atom chip with the help of an extra pair of anti-Helmholtz coils.
We experimentally demonstrate the trapping of 85 Rb atoms directly on a chip-size U-shaped magneto-optical trap (U-MOT). The trap includes a U-shaped wire on the chip, two bias magnetic field coils and laser beams. The capture volume of the U-MOT is theoretically calculated, and the trap is experimentally realized. With 2 A current applied to the U-shaped wire and 2-Gauss horizontal bias field, more than 2 × 10 6 atoms are trapped. In contrast with an ordinary mirror-MOT, this U-MOT captures atoms directly from the background, thus the trap size is greatly reduced. Based on this mini trap scheme, it is possible to realize a chip-size atom trap array for quantum information processing.
We propose a novel controllable double-well magneto-optical trap (MOT) by using a square current-carrying wire and a bias magnetic field. The spatial distributions of the magnetic fields and their gradients are calculated, and the results show that the proposed trap has double magnetic wells with two centres of zero magnetic field and can be continuously evolved as a single-well trap by reducing the current in the wire or increasing the bias field, which can be used to realize a controllable double-well MOT, even to prepare one- and two-dimensional arrays of magneto-optical lattices on the surface of an atom chip. We also estimate the number (~107) and temperature (~260 μK) of trapped cold atoms in our MOT.
We propose two novel double-well magnetic surface traps (i.e., a double-well U-U-shaped wire trap and a double-well U-Z-shaped wire trap) for cold atoms using a straight and U-shaped current-carrying wire or two U-shaped current-carrying wires. These double-well magnetic traps can be continuously changed into a single-well by reducing the current in a straight wire or an inner U-shaped wire from a suitable value to zero, and vice versa. The spatial distributions of the magnetic fields from two current-carrying wire layouts and their field gradients are calculated and analyzed, and the trapped atomic number and its temperature in each magnetic well are estimated. Our study shows that our double-well magnetic surface traps can be used to realize two-species magneto-optical traps (MOTs) above the surface of the wire plane. Under the approximation of low intensity, cold atomic samples with a captured number of ∼10^6 atoms and a temperature of approximately 270 µK can be obtained in each ^85Rb atomic MOT. Since each MOT in two-species MOTs can be prepared independently, our controllable double-well trap can be used to study the cold collisions between two different atomic samples.
In this paper, we have developed a combined magnetic field system to explore an alternative technical route for the generation of Bose–Einstein condensates containing numerous atoms on an atom chip. The system is characterized by the fact that the quadrupole magnetic field required by the magneto-optic trap is generated by U-shaped current-carrying wires combined with bias magnetic fields, whereas the quadrupole magnetic field adopted for the magnetic trap is generated by anti-Helmholtz coils. By fine-tuning the bias magnetic fields, the collection of atoms in the mirror MOT and the loading of the quadrupole magnetic trap can be optimized. The initial number of [Formula: see text]Rb atoms in the magnetic trap is approximately [Formula: see text], and the lifetime of the atoms is over 30 s. This scheme can facilitate the chip-surface design and is suitable for the precise manipulation of Bose–Einstein condensates near the chip surface.
We describe a dynamic magneto-optical trap (MOT) suitable for the use with vacuum systems in which optical access is limited to a single window. This technique facilitates the long-standing desire of producing integrated atom chips, many of which are likely to have severely restricted optical access compared with conventional vacuum chambers. This 'switching-MOT' relies on the synchronized pulsing of optical and magnetic fields at audio frequencies. The trap's beam geometry is obtained using a planar mirror surface, and does not require a patterned substrate or bulky optics inside the vacuum chamber. Central to the design is a novel magnetic field geometry that requires no external quadrupole or bias coils which leads toward a very compact system. We have implemented the trap for 85 Rb and shown that it is capable of capturing 2 million atoms and directly cooling below the Doppler temperature.
Abstract Atom chips provide flexible technologies for implementing modern concepts in quantum optics, quantum measurement, and quantum information processing. Atom chips are miniature devices that confine, control and manipulate cold atoms using electric, magnetic, and light fields. Due to the shrinkage of scale, arbitrary magnetic traps can be generated from current sources outside the chip’s vacuum compartment, in contrast to a traditional setup. This makes it easy to change trap configurations in an experiment that involves rapid prototyping of quantum states and quantum trajectory designs in free space. In this work, we show relevant parameters needed for transferring a cold atom cloud at the recoil limit from a magneto-optical trap (MOT) to an area close to the atom chip. To create a movable magnetic potential for this transfer, we used the MOT coils and an additional pair of coils in an anti-Helmholtz configuration. The properties of the movable potential were obtained by performing the Computer Simulation Tool (CST EM Studio suite®). Furthermore, an appropriate magnetic trap on a chip is developed, based on the simulation from COMSOL Multiphysics. We used a magnetic field gradient of around 20 G/cm to transport the cold atom with a distance over 20 mm with a temperature gain below 100 micro-Kelvin. The simulation results are based on an atom chip with a size of 2×2 cm2 and a copper wire thickness of 2 mm. The atom chip consists of Z, U and I-shaped wires that generate a quadrupole magnetic field. The resulting field minimum can be made at least 7 mm away from the chip surface.