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.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.

Physica ScriptaApr 13, 20160 citations

Double-Loop Microtrap Array for Ultracold Atoms

Bin Jian

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.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.

May 6, 20140 citations

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.