A high optical access cryogenic optical tweezer array

Arrays of single trapped neutral atoms are an emerging platform for quantum metrology, simulation, and information processing. They have seen the fastest qubit number scaling in the past few years. In this thesis, I present a set of new technologies, a cryogenic optical tweezer array and trapped single atoms using a metasurface focusing lens, that we developed for the next generation of optical tweezer platforms.

In the first part of the thesis, I describe a new apparatus that combines a cryogenic environment with high-NA optical access. We demonstrate a trapped array of single atoms with a vacuum-limited lifetime of up to 3000 seconds, which is difficult to achieve in room temperature tweezer experiments. Additionally, we characterize the heating of atoms in our apparatus and find no adverse effects from residual vibration introduced by the cryocooler. Interferometric measurements reveal residual vibration to be 2 nm RMS. With the long vacuum-limited lifetime, we measure imaging and cooling losses of trapped single atoms that can often be overwhelmed by vacuum loss in typical apparati. We demonstrate an imaging loss rate of 3.8(4) × 10⁻⁴ per 14 ms image, with an imaging assignment infidelity of 10⁻⁶ and a cooling loss rate of 5(4) × 10⁻⁵ per 25 ms cooling pulse, among the lowest reported in alkali atoms. We also demonstrate preliminary single qubit rotations with a microwave antenna within the cryogenic housing and characterize magnetic field fluctuations to 0.5 mG over a period of half an hour, comparable to other tweezer experiments.

In the second part of my thesis, I describe a new approach to manipulate and control trapped single atoms in optical tweezers through the use of optical metasurfaces. Optical metasurfaces are planar photonic elements composed of a periodic array of subwavelength dielectric nanostructures. These nanostructures couple, either resonantly or off-resonantly, and re-radiate the incoming light with a transformed phase, polarization, and amplitude determined by the nanostructure’s shape, size, and material composition. In this thesis, we create a 0.55 NA metasurface lens with a focusing efficiency of up to 58% to trap single atoms to sub-micron positional confinement, and detect single ⁸⁷Rb atoms though the same lens. We also perform field-of-view measurements and find a diffraction-limited field-of-view of ±10 µm, which is in good agreement with numerical simulation. Finally, I present potential future metalens designs with qualities beneficial for creating large neutral atom tweezer arrays, including a doublet lens with a large field-of-view of up to 2 mm, a lens without chromatic aberration, and polarization multiplexed lenses for dynamically changing the trapping potential or for achromatic imaging of the trapped atoms.