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arXiv:2603.17119

From MOT to BEC using a single crossed-wire pair

Joshua M. Wilson, James A. Stickney, Francisco Fonta, Johnathan White, Brian Kasch, Spencer E. Olson, Matthew B. Squires

physics.atom-phquant-phSubmitted Mar 17, 2026• Announced Mar 19, 2026• 0 citations
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Abstract

We demonstrate a new magneto-optical trap (MOT) configuration using a simple pair of crossed wires rotated at 45 deg and an appropriate bias field to generate a MOT of >10^8 atoms. The same pair of wires, with slightly adjusted control parameters, is then used to magnetically trap the atoms and cool them via forced evaporative cooling into a Bose-Einstein condensate (BEC) with >10^4 atoms. We present the theoretical framework for generating a quadrupole field using a pair of crossed wires with arbitrary rotation angle, along with the atom chip design and fabrication. Finally, we describe the experimental protocols required for BEC production using only a single crossed-wire atom chip.

Comments
6 pages, 5 figures. Approved for public release; distribution is unlimited (AFRL-2026-0090)

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We demonstrate a new magneto-optical trap (MOT) configuration using a simple pair of crossed wires rotated at 45 deg and an appropriate bias field to generate a MOT of >10^8 atoms. The same pair of wires, with slightly adjusted control parameters, is then used to magnetically trap the atoms and cool them via forced evaporative cooling into a Bose-Einstein condensate (BEC) with >10^4 atoms.
We present the theoretical framework for generating a quadrupole field using a pair of crossed wires with arbitrary rotation angle, along with the atom chip design and fabrication. Finally, we describe the experimental protocols required for BEC production using only a single crossed-wire atom chip.
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 report the realization of Bose-Einstein condensation (BEC) of metastable helium atoms using an in-vacuum coil magnetic trap and a crossed-beam optical dipole trap. A quadrupole-Ioffe configuration magnetic trap made from in-vacuum hollow copper tubes provides fast switching times while generating traps with a 10-G bias, without compromising optical access. The bias enables in-trap one-dimensional Doppler cooling to be used, which is the only cooling stage between the magneto-optic trap and the optical dipole trap. This allows direct transfer to the dipole trap without the need for any additional evaporative cooling in the magnetic trap. The entire experimental sequence takes 3.3 s, with essentially pure BECs observed with $\ensuremath{\sim}{10}^{6}$ atoms after evaporative cooling in the dipole trap.
Abstract We propose a new miniature Bose–Einstein condensate (BEC) system based on a transparent atom chip with a compact external coil structure. A standard six-beam macroscopic magneto-optical trap (MOT) is able to be created near the chip surface due to the chip’s transparency. A novel wire pattern consisting of a double-z wire and a z-shaped wire is designed on the transparent atom chip. With a vertical bias magnetic field, the double-z wire can create the quadrupole magnetic field of an intermediate chip MOT, which is suitable for transporting atoms from the macroscopic MOT to the chip z-wire trap efficiently. The compact external coil structure is designed with a rectangular frameless geometry consisting of only four coil pairs and its volume is less than 0.3 liters. The maximum system power consumption during the BEC generation procedure is about 45 W. The miniature system is evaluated, and about 3 × 10 6 atoms can be loaded into the chip z-wire trap. The miniature chip BEC system has the advantages of small volume and low power consumption, and it has great potential for practical applications of BEC.
This work has investigated the Magneto-Optical Trap (MOT) system used to produce Bose-Einstein Condensate (BEC). A primary challenge addressed in this study concerns the geometric limitations of traditional single-pair anti-Helmholtz coil configurations, where the magnetic field peaks occur outside the accessible inter-coil region. To overcome this limitation, we have explored the use of double-pair anti-Helmholtz coil configurations that create well-shaped magnetic field potentials centered at the experimentally accessible z=0z=0z=0 location. This investigation encompasses the three sequential processes of atom cooling: cooling in a linear external magnetic field through Doppler cooling, cooling in a well-shaped magnetic field through trapping, and evaporative cooling of atoms to achieve sub-microkelvin temperatures. Through theoretical analysis and numerical simulation, we have determined optimal geometric parameters for the coil configuration and operational parameters including laser detuning, saturation intensity, and initial atom populations for 87Rb{}^{87}\text{Rb}87Rb BEC production. The results indicate that with the optimized configuration, the system can achieve final temperatures of approximately Tf∼60 nKT_f \sim 60\,\mathrm{nK}Tf​∼60nK and produce condensate populations of ∼105\sim 10^5∼105 atoms with a mean density of n0=4.9×1015 m−3n_0 = 4.9 \times 10^{15}\,\mathrm{m}^{-3}n0​=4.9×1015m−3, providing systematic design guidance for experimental BEC systems
The apparatus and procedure required to generate a pure Bose-Einstein condensate (BEC) consisting of about half a million 87Rb atoms at a temperature of <60 nK with a phase density of >54 is described. The atoms are first laser cooled in a vapour cell magneto-optical trap (MOT) and subsequently transferred to an ultra-low pressure MOT. The atoms are loaded into a QUIC trap consisting of a pair of quadrupole coils and a Ioffe coil that generates a small finite magnetic field at the trap energy minimum to suppress Majorana transitions. Evaporation induced by an RF field lowers the temperature permitting the transition to BEC to be observed by monitoring the free expansion of the atoms after the trapping fields have been switched off.PACS Nos.: 03.75.Fi, 05.30.Jp, 32.80.Pj, 64.60.–i