Optical nanofiber fabrication and analysis towards coupling atoms to superconducting qubits

Abstract

We describe advancements towards coupling superconducting qubits to neutral atoms. To produce a measurably large coupling, the atoms will need to be on the order of a few micrometers away from the qubit. A consequence of combining superconducting qubits and atoms is addressing their operational constraints, such as the deleterious light effects on superconducting systems and the magnetic field sensitivity of superconducting qubits. Our group proposes the use of optical-nanofiber-based optical dipole traps to confine atoms near the superconductor. Optical nanofibers (ONFs) have high-intensity evanescent waves that require less power than equivalent standard dipole traps. This thesis focuses on the fabrication and analysis of the behavior of ONFs. First we present the construction of the pulling apparatus. We outline the necessary steps for a typical pull, detailing the cleaning and alignment process. Then we examine the quality of the fibers by measuring their transmission and comparing our results to other reported measurements, demonstrating a two-order of magnitude decrease in loss. Next we present the modal evolution in ONFs using simulations and spectrogram analysis. We identify crucial elements to improve the transmission and demonstrate understanding of the modal dynamics during the pull. Then we study higher-order modes (HOMs) with ONFs using the first excited TE01, TM01, and HE21 modes. We demonstrate transmissions greater than 97% for 780 nm light when we launch the first excited LP11 family of modes through fibers with a 350 nm waist. This setup enables us to launch these three modes with high purity at the output, where less than 1% of the light is coupled to the fundamental mode. We then focus on the identification of modes on the ONF waist. First we use Rayleigh scattering to identify the modal content of an ONF. Bulk optics can convert the modes in the ONF, and we observe the controllable conversion of superpositions of modes. Finally, we use an evanescently-coupled tapered optical fiber probe that allows for the identification of the fundamental mode beating with HOMs and compare the results to simulations.