Sub-micron period lattice structures of magnetic microtraps for ultracold atoms on an atom chip

Abstract

We report on the design, fabrication and characterization of magnetic nanostructures to create a lattice of magnetic traps with sub-micron period for trapping ultracold atoms. These magnetic nanostructures were fabricated by patterning a Co/Pd multilayered magnetic film grown on a silicon substrate using high precision e-beam lithography and reactive ion etching. The Co/Pd film was chosen for its small grain size and high remanent magnetization and coercivity. The fabricated structures are designed to magnetically trap 87 Rb atoms above the surface of the magnetic film with 1D and 2D (triangular and square) lattice geometries and sub-micron period. Such magnetic lattices can be used for quantum tunneling and quantum simulation experiments, including using geometries and periods that may be inaccessible with optical lattices.

Radio-frequency spectroscopy of a linear array of Bose-Einstein condensates in a magnetic lattice

“…We have recently fabricated magnetic microstructures with periods down to 0.7 /xm to create ID and 2D square and triangular magnetic lattices in which the tunneling times between neighboring lattice sites are estimated to be of the order of tens of milliseconds [10]. To perform quantum tun neling experiments in a 0.7-/xm magnetic lattice a number of challenges need to be considered.…”

“…First, high-quality magnetic potentials that are smooth and highly periodic (to better than 023605-10 1%) are needed in order to minimize effects due to disorder and any fragmentation of the elongated atom clouds. Second, the atoms will be trapped at distances of typically 0.35 /xm from the chip surface, and therefore, surface effects such as attractive van der Waals forces and thermally induced spin flips produced by thermal currents in the nearby conducting film need to be considered [7,10]. Third, in order to operate at the barrier heights required for quantum tunneling experiments (e.g., V0 = 12Er -20 mG for 87Rb F -1 atoms, where E, = ~\ ) , stray magnetic fields and magnetic noise need to be compensated to better than 1 mG.…”

“…Magnetic lattices comprising periodic arrays of magnetic microtraps created by patterned magnetic films [1][2][3][4][5][6][7][8][9][10] provide a potentially powerful complementary tool to optical lat tices for simulating many-body condensed-matter phenomena. Such lattices offer a high degree of design flexibility.…”

“…To date, ultracold atoms have been successfully loaded into a one-dimensional magnetic lattice with a period of 10 gm [3,8], a two-dimensional rectangular magnetic lattice with a period of about 25 gm [2,4,7], and square and triangular magnetic lattices with a period of 10 gm [9]. Two-dimensional square and triangular magnetic lattices with periods down to 0.7 gm, designed for quantum tunneling experiments, have recently been fabricated and characterized [10],…”

Radio-frequency dressed lattices for ultracold alkali atoms

“…The lattice constant of the periodic landscapes produced by such schemes ranges from a few mm down to 10 μm, and is limited by fabrication technology and near-surface effects [10]. Recent proposals suggest that this atom-chip approach can, in principle, create arrays of magnetic traps with submicron periodicity, located a few hundred nanometers away from the chip surface [21,22]. Experimental realization of such proposals face technical challenges associated with the complexity of their fabrication and from the short surface-atom distance which enhances near surface effects.…”