Deep and Periodically Driven Optical Lattices for Fundamental Physics

• Main Author: Cardman, Ryan James
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2023
• Subjects: Atomic physics; Optics; Physics
• ISBN: 9798380373517

Fundamental physics is concerned with the problems of defining fundamental constants, units of measurement, and searching for new forces and aspects of matter. Usually, the best way to resolve these inquiries is to have a precise knowledge of atomic energy levels and the transition frequencies in order for their quantum states to be manipulated. Spectroscopy is a tool that probes these atomic energy levels by observing the atom’s response as the energy of the applied radiation is varied. Over the past century, spectroscopy using electromagnetic radiation has involved direct interactions with the atom’s electric and magnetic multipole moments via the A · p term of the minimal coupling Hamiltonian. The work presented in this thesis utilizes such interactions with laser fields and goes a step further by exploring a novel light-matter interaction via the A2 term.Leading problems in the field of fundamental physics include the commercialization of optical frequency standards with short-term stabilities beating 10−11/ √τ and the discovery of new science arising from competitive precision measurements of the Rydberg constant and the detection of axion dark matter. Ultracold rubidium atoms subject to periodic optical potentials in standing waves of light known as optical lattices offer solutions to these problems. Rubidium atoms contained in miniaturized, glass vapor cells can be probed with a 778-nm laser in order to obtain the |5S⟩ → |5D⟩ transition frequency as a portable optical frequency standard. Optical traps can induce shifts that compensate those incurred by the probing lasers and confine the atoms to prevent residual Doppler effects, both of which would otherwise hamper the clock stability. Addressing the other two problems mentioned, circular-state Rydberg atoms that are able to be manipulated with optical lattices introduce a platform for high-resolution spectroscopy of their electronic transitions using very weak microwave fields. The long lifetimes of circular states, which approach 1 s, extend the probing times for a measurement of the Rydberg constant (10−12 uncertainty) insensitive to the proton charge radius, and the existence of microwaves generated by axion couplings to the electromagnetic field. This dissertation explores the functionality of optical lattices as a tool that can contribute to the advancement of these aforementioned endeavors.In the first implementation of optical lattices for these goals, a measurement of the Rb |5D3/2⟩ AC polarizability and photoionization cross section is performed using a cavity-enhanced optical lattice with an ultra-deep depth on the order of ∼ 105 single-photon recoils. The lattice wavelength is λ = 1.064 µm, which induces shifts on |5D3/2⟩ that can be characterized by the measured scalar polarizability of αS/5D3/2 = −524(17) atomic units. I choose this wavelength because it is commonly available as a narrow-linewidth, high-powered laser. At this wavelength, photoionization induces decay of this energy level and broadening of spectral lines as evidence of the significant measured cross section σP I = 44(1) Mb.The secondary use of lattices as a tool for fundamental physics concerns periodically driven ponderomotive potentials for the effort of initializing the circular states required for a Rydberg constant measurement and dark-matter detection. Experimentally, the principles are discussed in a newly developed lattice phase-modulation technique, where the |46S1/2⟩ → |46P1/2⟩ and |48S1/2⟩ → |49S1/2⟩ transitions were spectrocscopically measured with this driving mechanism. Additionally, the importance of cancelling stray electric and magnetic fields for this mechanism to be efficient is also demonstrated. The applicability of ponderomotive light-matter interactions for obtaining circular states is discussed in a theoretical proposal of all-optical circularization techniques.