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Chinese Optics Letters

Efficient cold atom source from a single-layer atom chip

P. I. Skakunenko, Dar'ya V. Bykova, Anton E. Afanasiev, Alexey S. Kalmykov, Roman V. Kirtaev, V. I. Balykin

Published Jan 1, 2024• 5 citations
Publisher

Abstract

We developed a new single-layer atom chip with an additional U-shaped current-carrying structure.The new U-shaped microwire creates optimized magnetic field distribution, which increases the trapping volume of a magneto-optical trap (MOT) near the chip.Our approach allows one to localize more atoms, while a setup remains relatively simple (single-layer approach) and consumes low current (up to 10 A).The total number of trapped 87 Rb atoms in our setup is 5 × 10 7 .

DOI
10.3788/col202422.060201

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We developed a new single-layer atom chip with an additional U-shaped current-carrying structure.The new U-shaped microwire creates optimized magnetic field distribution, which increases the trapping volume of a magneto-optical trap (MOT) near the chip.Our approach allows one to localize more atoms, while a setup remains relatively simple (single-layer approach) and consumes low current (up to 10 A).The total number of trapped 87 Rb atoms in our setup is 5 × 10 7 .
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.
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.
With a movable quadrupole magnetic trap (QMT) generated by two pairs of partly-overlapped magneto-optical trap (MOT) and transfer coils, a highly efficient transport of cold87Rb atoms to the atom chip surface is realized. By the QMT movable means of linearly increasing the current in the transfer coils but simultaneously keeping the current in the MOT coils constant, the velocity profile of the moving trap is Blackman-type-like. With this QMT movable scheme, the cold atoms are transferred to the atom chip surface from the MOT center. In the transfer process, the cold atom temperature is increased by about 30 μK, and the transfer efficiency is above 90%. This system provides an appropriate cold atoms source for the atom chip interferometer and also can be used to investigate the interaction between atom and chip surface. ? 2016, Chinese Lasers Press. All right reserved.
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.
The single-beam magneto-optical trap (MOT) based on the diffractive optical element offers a new route to develop compact cold atom sources. However, the optical efficiency in the previous single-beam MOT systems is usually low and unbalanced, which will affect the quality of the trapped atoms. To solve this issue, we developed a centimeter-scale dielectric metasurface optical chip with dynamic phase distributions, which was used to split a single incident laser beam into five separate ones with well-defined polarization states and uniform energy distributions. The measured diffraction efficiency of the metasurface is up to 47%. A single-beam MOT integrated with the metasurface optical chip was then used to trap the 87 Rb atoms with numbers ∼1.4 × 10 8 and temperatures ∼7.0 μK. The proposed concept in this work may provide a promising solution for developing ultracompact cold atom sources.
The role of U-wire generated quadrupole-like magnetic field profile on loading of cold 87Rb atoms in a magneto-optical trap (MOT) on atom-chip has been investigated. It is shown by simulations that the quadrupole field profile and the centre of the quadrupole field vary depending upon the U-wire current and bias field values. Moreover, the resemblance of generated field profile to the ideal quadrupole field critically depends on the values of current in U-wire and bias magnetic field. The observed number of trapped atoms in the MOT and its position has also been found to depend on the quadrupole field profile. The number of trapped atoms in the MOT reaches maximum when the field profile approaches close to an ideal quadrupole field. These studies are, in general, useful in optimizing the number in the MOT before transfer of these cold atoms to the microtraps of an atom-chip.