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Double-Loop Microtrap Array for Ultracold Atoms

Bin Jian

Published May 6, 2014• 0 citations
OpenAlex

Abstract

A novel kind of magnetic microtrap is demonstrated for ultracold neutral atoms. It consists of two concentric loops of radii $r_1$ and $r_2$ having oppositely oriented currents. A magnetic field minimum is generated in three dimensions that can be used to trap the atoms with a trap depth of about 1 mK using a current of 2.6 A. The condition $r_2/r_1$ = 2.2 maximizes the restoring force on the atoms toward the trap center. Unlike conventional magnetic microtraps, an external bias field is not required. Moreover, a one dimensional array of double-loop microtraps can be created by daisy chaining single microtrap circuits. \nA linear array of three microtraps having $r_1$ = 300 $\\mu$m was fabricated as part of an atom chip. The following three techniques were developed to load the microtrap array: 1) atoms initially contained in a magneto-optical trap (MOT) were transported to the atom chip by a conventional magnetic trap, 2) atoms were first loaded into a mirror MOT and 3) atoms were initially loaded in a far off resonance optical dipole trap (FORT). Each technique loaded greater than $10^5$ $^{87}$Rb atoms into the microtrap array. The lowest temperature of 30 $\\mu$K for the microtrapped atom cloud was achieved using FORT loading. The strength and the position of the microtrap could be precisely adjusted over a range from 300 to 50 $\\mu$m above the atom chip surface by applying an external bias magnetic field. The lifetime of the atoms trapped in the microtrap array was measured to be 350 ms which was limited by the collisions with residual background gas.

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Optics Express•Jan 1, 2006•9 citations
A novel kind of magnetic microtrap is demonstrated for ultracold neutral atoms. It consists of two concentric loops of radii r1r_1r1​ and r2r_2r2​ having oppositely oriented currents. A magnetic field minimum is generated in three dimensions that can be used to trap the atoms with a trap depth of about 1 mK using a current of 2.6 A. The condition r2/r1r_2/r_1r2​/r1​ = 2.2 maximizes the restoring force on the atoms toward the trap center. Unlike conventional magnetic microtraps, an external bias field is not required. Moreover, a one dimensional array of double-loop microtraps can be created by daisy chaining single microtrap circuits. \nA linear array of three microtraps having r1r_1r1​ = 300 mu\\mumum was fabricated as part of an atom chip. The following three techniques were developed to load the microtrap array: 1) atoms initially contained in a magneto-optical trap (MOT) were transported to the atom chip by a conventional magnetic trap, 2) atoms were first loaded into a mirror MOT and 3) atoms were initially loaded in a far off resonance optical dipole trap (FORT). Each technique loaded greater than 10510^5105 87^{87}87Rb atoms into the microtrap array. The lowest temperature of 30 mu\\mumuK for the microtrapped atom cloud was achieved using FORT loading. The strength and the position of the microtrap could be precisely adjusted over a range from 300 to 50 mu\\mumum above the atom chip surface by applying an external bias magnetic field. The lifetime of the atoms trapped in the microtrap array was measured to be 350 ms which was limited by the collisions with residual background gas.
A microtrap consisting of two concentric circular wire loops having radii of 300 and 660 μm, respectively, is demonstrated. The three-dimensional trap has a maximum depth of more than 1 mK, and the trap center position as measured below the atom chip surface can be adjusted by applying a small-bias magnetic field. More than 105 Rb87 atoms were transferred into the microtrap from a magneto-optical trap and remained trapped for several hundred milliseconds, which is limited by the background pressure. The loading of a linear array of three microtraps is also demonstrated. The trap dimensions are readily scaled to micrometer size, which is of interest for creating a one- and two-dimensional array of neutral atom traps on a single atom chip.
A microtrap consisting of two concentric circular wire loops having radii of 300 and 660 μm, respectively, is demonstrated. The three-dimensional trap has a maximum depth of more than 1 mK, and the trap center position as measured below the atom chip surface can be adjusted by applying a small-bias magnetic field. More than 105 Rb87 atoms were transferred into the microtrap from a magneto-optical trap and remained trapped for several hundred milliseconds, which is limited by the background pressure. The loading of a linear array of three microtraps is also demonstrated. The trap dimensions are readily scaled to micrometer size, which is of interest for creating a one- and two-dimensional array of neutral atom traps on a single atom chip.
A linear array of 11 closely spaced microtraps was demonstrated. Each microtrap was created using the magnetic field generated by two concentric circular wire loops having radii of 60 and 132 μ m carrying oppositely oriented currents as well as a bias magnetic field oriented perpendicular to the atom chip surface containing the microwire loops. 87 Rb atoms were initially cooled using either a surface magneto-optical trap (MOT) or a far off resonance optical dipole trap (FORT) created using an infrared laser directed along the microtrap array axis. The microtrap current was turned on and over 12 000 atoms were loaded into each microtrap. The advantage of FORT loading was that the 11 microtraps were about equally populated and the microtrapped atom temperature of 11 μ K was one quarter of that obtained using the MOT.
Abstract Ultracold atoms created using microtraps are being used in an increasing number of diverse applications. This paper reviews the double-loop microtrap which consists of two concentric circular wire loops carrying oppositely oriented currents. This generates a magnetic field configuration that traps a magnetic dipole in three-dimensions. The position of the trapped atoms relative to the atom chip surface containing the microwire loops, can be precisely controlled by applying different currents in the two loops or alternatively using a so called bias magnetic field oriented perpendicular to the chip surface. Double-loop microtraps can be daisy chained in series to create a one- or two-dimensional microtrap array. Experiments that have demonstrated a double-loop microtrap array are discussed. Future possibilities are presented as to how atoms can be transferred between adjacent microtraps as well as the use of an additional micro sized Ioffe coil to create a trap having a nonzero magnetic field minimum to reduce atom loss by suppressing Majorana transitions.
We propose a wire configuration to create a one-dimensional (1D) array of magnetic microtraps for trapping ultracold atoms. The configuration is formed by replacing the central part of the Z-wire pattern with a zigzag wire. We simulate the performance of this pattern by the finite element method which can take both the width and depth of the wire into consideration. The result of simulation shows that this configuration can create magnetic microtraps which can be separated and combined by changing the bias magnetic field. We manage to split the Z-wire trap and prove that a similar result can occur for the new wire configuration. The fabrication processes of the atom chip are also introduced. Finally we discuss the loading method.
An array of square current-carrying wires is proposed to construct a two-dimensional (2D) array of surface magneto-optical traps and Ioffe magnetic ones for realizing a 2D lattice of Bose-Einstein condensations (BECs) on an atom chip. Our study shows that when a vertical homogeneous bias magnetic field is only used, the wires will form a 2D array of quadrupole magnetic traps, which can be used to construct 2D lattice of surface magneto-optical micro-traps. While another horizontal homogeneous bias field is added simultaneously, the above 2D array of quadrupole micro-traps will be changed as an array of surface Ioffe micro-traps, which can be used to form a 2D magnetic lattice and then realize a 2D array of BECs. The dynamic loading process of cold (87)Rb atoms from each micro-MOT into Ioffe micro-trap is studied by using Monte-Carlo simulations, and our results show that the scheme can be used to realize a natural and effective loading of cold atoms from 2D array of micro-MOTs into 2D array of Ioffe micro-traps, and the loading efficiency can be reach ~ 65%. Moreover, the positions of each BEC (or MOT) in 2D array of magnetic micro-traps can be controlled by adjusting the currents in the wires or by changing the additional vertical bias field.