Trapping ultracold atoms in submicron period magnetic lattices

Tien Tran, Yibo Wang, Ivan Herrera, A. Balcytis, D. Nissen, M. Albrecht, S. Whitlock, Andrei Sidorov, Peter Hannaford, Arnan Mitchell, Halina Rubinsztein-Dunlop
2019 AOS Australian Conference on Optical Fibre Technology (ACOFT) and Australian Conference on Optics, Lasers, and Spectroscopy (ACOLS) 2019  
Periodic arrays of magnetic microtraps patterned on a magnetic film provide a potential complementary tool to conventional optical lattices. Such magnetic lattices allow a high degree of design flexibility, low technical noise and state-selective trapping of atoms. This thesis reports the trapping of ultracold 87 Rb atoms in 0.7 µm-period triangular and square magnetic lattices integrated on an atom chip as a step towards using magnetic lattices as a platform for simulating condensed matter and
more » ... quantum many-body phenomena in nontrivial lattice geometries. The new generation sub-micron period magnetic lattices are produced by patterning a Co/Pd multi-atomic layer magnetic film deposited on a silicon substrate using electron-beam lithography and reactive ion-etching. The magnetic microstructures include 0.7 µm-period 2D square and triangular lattices and 1D 0.7 µm-period and 5 µm-period lattices. The four magnetic microstructures are mounted on an atom chip containing two Z-shaped and two U-shaped current-carrying wires fabricated by chemical etching on a direct bonded copper (DBC) board. The current-carrying wires are required for initial preparation of the ultracold 87 Rb atoms, allowing the creation of a Bose-Einstein condensate in a Z-wire trap and loading into the magnetic lattice. The magnetic lattice potential is produced by applying a bias magnetic field to the magnetic lattice structures which in the case of the 0.7 µm-period lattice produce extremely tight magnetic microtraps with trap frequencies up to about 800 kHz and trap bottoms at estimated distances down to about 90 nm from the chip surface. The atom-surface interaction is studied by measuring the atom loss when atoms in the Z-wire magnetic trap are brought to various distances very close to the chip surface. The interaction of the atoms with the magnetic trapping potential is investigated by launching the Z-wire trap cloud vertically towards the magnetic lattice structures under different bias magnetic fields. The key results presented in this thesis are the successful loading of ultracold atoms into the 0.7 µm-period 2D triangular and square magnetic lattices. The mea-iii sured trap lifetimes range from 0.4 to 2.5 ms, and increase approximately linearly with increasing distance from the chip surface. The relatively short trap lifetimes are attributed mainly to losses due to surface-induced thermal evaporation when loading into the tight magnetic lattice traps rather than to fundamental loss processes such as three-body recombination or spin-flips due to Johnson noise from the chip surface. The Casimir-Polder interaction starts to become significant at distances less than about 100 nm from the chip surface. To the best of my knowledge, these results represent the first reported realization of trapping of atoms in a sub-micron period magnetic lattice. This is considered to be a significant step towards employing magnetic lattices for the simulation of condensed matter and many-body phenomena in nontrivial lattice geometries. iv v
doi:10.1117/12.2539581 fatcat:kbazzfkgkfdmditatqtnxpzocy