Effect of Environment on the Fidelity of Control and Measurements of Solid-State Quantum Devices.

摘要

This thesis addresses the origin and effect of noise and fluctuations in quantum devices that find applications in quantum information processing. In the first half of the thesis, we consider a phenomenological model of the noise and study its effect on the fidelity of quantum measurements and operations that are essential for quantum computing. We focus primarily on quantum gate operations in phase qubits, detection of microwave photons and the measurement of the Berry curvature. Specifically, we examine the effect of the Ohmic noise on optimally controlled flux-biased phase qubits for one- and two-quadrature microwave pulses and demonstrate that twoquadrature pulses with fixed driving frequency are as robust as variable driving frequency, in the presence of environment. Next, we present a model to analyze the quantum efficiency of a microwave photon detector based on a current-biased Josephson junction and study the effect of decoherence on the detection efficiency of the detector. We also present alternative set-ups for microwave photon detection and provide a systematic method to compute the power absorbed by the detector. We then consider the effect of decoherence on the Berry curvature measurement, which employs a novel non-adiabatic protocol, and show that the curvature is immune to decoherence. In the second half of the thesis, we go beyond the phenomenological models of the noises and perform a detailed study of the microscopic description of the Johnson noise. Here we focus primarily on quantum dot devices. We present a formalism to compute relaxation rates in charge and spin qubits due to evanescent wave Johnson noise (EWJN) from the metallic gates that are in proximity to quantum dots. The EWJN is analyzed for the metallic gates that are characterized by both local and nonlocal dielectric response functions.