Trapping Ultracold Atoms in a Sub-Micron-Period Triangular Magnetic Lattice Y. Wang, 1 T. Tran, 1 P. Surendran, 1 I. Herrera, 1, 2 A. Balcytis, 3, 4, 5 D. Nissen, 6 M. Albrecht, 6 A. Sidorov, 1 and P. Hannaford 1 1 Centre for Quantum and Optical Science, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia 2 Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand 3 Centre for Micro-Photonics, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia 4 Melbourne Centre for Nanofabrication, Victorian Node of the Australian National Fabrication Facility, 151 Wellington Rd., Clayton, Victoria 3168, Australia 5 Centre for Physical Sciences and Technology, Savanoriu Ave 2131, LT-02300 Vilnius, Lithuania 6 Experimental Physics IV, Institute of Physics, University of Augsburg, Universit¨ atstrasse 1, D-86159 Augsburg, Germany (Dated: October 14, 2018) We report the trapping of ultracold 87 Rb atoms in a 0.7 μm-period two-dimensional triangular magnetic lattice on an atom chip. The magnetic lattice is created by a lithographically patterned magnetic Co/Pd multilayer film plus bias fields. Rubidium atoms in the |F =1,mF = −1〉 low- field seeking state are trapped at estimated distances down to about 100 nm from the chip surface and with calculated mean trapping frequencies up to about 800 kHz. The measured lifetimes of the atoms trapped in the magnetic lattice are in the range 0.4 - 1.7 ms, depending on distance from the chip surface. Model calculations suggest the trap lifetimes are currently limited mainly by losses due to one-dimensional thermal evaporation following loading of the atoms from the Z-wire trap into the very tight magnetic lattice traps, rather than by fundamental loss processes such as surface interactions, three-body recombination or spin flips due to Johnson magnetic noise. The trapping of atoms in a 0.7 μm-period magnetic lattice represents a significant step towards using magnetic lattices for quantum tunneling experiments and to simulate condensed matter and many- body phenomena in nontrivial lattice geometries. I. INTRODUCTION Magnetic lattices consisting of periodic arrays of mi- crotraps created by patterned magnetic films on an atom chip provide a potential complementary tool to optical lattices for simulating condensed matter and many-body phenomena (e.g., [1]). Such lattices have a high de- gree of flexibility and may, in principle, be fabricated with almost arbitrary two-dimensional (2D) and one- dimensional (1D) geometries and lattice spacing [2] and may be readily scaled up. In addition, magnetic lattices do not require high power, stable laser beams and pre- cise beam alignment, they operate with relatively little technical noise, power consumption, or heating, and they involve state-selective atom trapping, allowing rf evapo- rative cooling to be performed in the lattice and rf spec- troscopy to be used to characterize the lattice-trapped atoms in situ. Finally, magnetic lattices have the poten- tial to enable miniaturized integrated quantum technolo- gies exploiting many-body states of ultracold atoms and hybrid quantum systems such as quantum registers with on-chip readout. However, magnetic lattices are still in their infancy compared with optical lattices due largely to the difficulty in fabricating high-quality magnetic microstructures, es- pecially lattices with sufficiently small periods to enable quantum tunneling experiments. To date, 1D magnetic lattices [3–5] and 2D rectangular [6, 7], square [8, 9] and triangular [8, 9] magnetic lattices with periods down to 10 µm have been produced and clouds of ultracold atoms have been trapped in them [3–7, 10]. In the case of the 10 µm-period 1D magnetic lattice, 87 Rb atoms have been cooled to degeneracy to create a periodic array of isolated Bose-Einstein condensates [4, 5]. In order to conduct experiments involving quantum tunneling, lat- tices with periods in the sub-micron regime are required (e.g., [11, 12]). In this paper we report the trapping of ultracold 87 Rb |F =1,m F = −1〉 atoms in a 0.7 µm-period triangular magnetic lattice on an atom chip. The magnetic lattice is created by a lithographically patterned magnetic Co/Pd multilayer film plus bias fields [9]. The design of the tri- angular magnetic lattice and calculations of the lattice trapping potentials including the effect of the Casimir- Polder surface interaction are presented in Sec. II. Sec. III gives experimental details, including the fabrication and characterization of the 0.7 µm-period triangular magnetic lattice structure. In Sec. IV we present experimental results for the interaction of the ultracold atoms with the magnetic lattice potential, loading of atoms into the magnetic lattice traps, and lifetime measurements of the lattice-trapped atoms at various distances from the chip surface. In Sec. V we discuss possible ways for improving the lifetimes and the loading procedure, and in Sec. VI we summarize our results. II. THE SUB-MICRON-PERIOD TRIANGULAR MAGNETIC LATTICE The triangular magnetic lattice structure is designed using the linear programming algorithm developed by arXiv:1705.09419v2 [physics.atom-ph] 9 Aug 2017