Rydberg Physics in a Cryogenic System for Hybrid Quantum Interfaces PDF Download

Author: Juan Camilo Bohorquez (Ph.D.)
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Languages : en
Pages : 0

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Book Description
This thesis summarizes the hardware constructed for the Hybrid experiment, as well as the experimental progress made in Hybrid, to enable the construction of a Hybrid quantum system. This systems seeks to couple neutral atoms to high quality factor microwave cavities. Cavity QED systems, such as this one, are an integral part of atom-superconducting hybrid quantum computing. These systems are also promising candidates for transduction of quantum information from the microwave to the optical regime. Such transduction would enable the quantum networking of superconducting (SC) quantum registers at long distances. Rydberg atoms are uniquely suited to such cavity QED systems owing to the strong dipole moments of microwave-frequency Rydberg-Rydberg transitions, and the accessibility of optical transitions. Though the development of such systems is made challenging due to the significant dc polarizability of Rydberg states, and the size of electric field noise near surfaces. This thesis outlines the application of a microwave dressing scheme to a Rydberg system, and a demonstration of the reduction of polarizability said states by a factor of 7. In addition, we summarize modeling and analysis of the dressed-atom system, and how such a dressing scheme can be engineered to fully null the polarizability of a Rydberg state in one direction. We also summarize the limits of the dressing scheme, namely the anisotropy of the polarizability of the dressed Rydberg states, where in one direction the polarizability may be fully nulled, but in normal directions the polarizability is only reduced by 50[percent]. We also demonstrate and discuss the enhanced fourth-order, hyperpolarizability, of the dressed Rydberg states, and how even in relatively weak dc fields (~ 20 mV/cm) these effects can come to dominate the un-dressed polarizability. Through these drawbacks, coupled with a study of the published efforts to understand and mitigate electric field noise from surfaces, we conclude that a dressing scheme alone will be insufficient to enable high-fidelity Rydberg cavity QED demonstrations in our device on its own. Such efforts would require a greater atom-surface distance, as well as the implementation of significant dc surface field noise mitigation and compensation techniques, in conjunction with the dressing scheme proposed, to produce the required fidelity of atom-cavity interactions. This thesis then discusses the first demonstration of Rydberg Rabi excitations via a novel quadrupole-dipole two-photon excitation scheme. This scheme presents a significant reduction in the Doppler-shift induced dephasing in finite temperature atomic systems, due to the significantly reduced k-vector mismatch between the counter-propagating Rydberg fields. This thesis presents an analytical model for understanding the quadrupole excitation dynamics, as well as the two-photon Rabi dynamics of the driven system, in the adiabatic regime. This thesis also uses a tool to solve the master equation to evaluate the validity of the {adiabatic elimination} approximation in our system. We then uses those analytical and numerical tools to engineer the Rydberg laser polarizations, frequencies and powers for improved Rabi flopping fidelity. The analytical treatment is followed up with experimental date, demonstrating the Rydberg Rabi flopping between the ground state and $\ds 52P_{3/2},m_j=1/2$ Rydberg state. We supplement the experimental data, and analysis of it with a detailed accounting of the parameters of the Rydberg laser fields and noise sources which degrade the fidelity of the Rydberg Rabi operations, as measured {in situ}, or calibrated externally. Finally this thesis present a path forward for the Hybrid experiment, considering the challenges presented by surface electric field noise. The upgraded design for the experimental system makes use of a bulk microwave resonator, designed to require much greater atom-surface distances inside the atom-cavity interaction region. This device would enable atom-cavity interactions for cavity frequencies in the 5-7 GHz band, the native operating frequencies of existing SC quantum systems, while allowing the users to mitigate the size and effects of surface electric fields. We discuss the design considerations and current status of the new cavity design, as well as the design of the optical trapping, transport and readout techniques which will be used to localize and control the atoms inside the interaction region.