CHARACTERIZATION AND REMOVAL OF NOISE IN QUANTUM SYSTEMS WITH PULSES

QI JIAAN

Publication

CHARACTERIZATION AND REMOVAL OF NOISE IN QUANTUM SYSTEMS WITH PULSES

QI JIAAN

Abstract

This thesis studies noisy quantum channels under the influence of external pulses, which interacts with a quantum register in meaningful ways that allow characterization or removal of the noise. For the randomized benchmarking (RB) protocol, a popular scheme to measure the noise level, we study the scenarios where the conventional weak gate-dependance and weak time-correlation noise assumptions are violated. For gate-dependent noise, we show that the "RB number" does not upper-bound the average gate-set infidelity, a number it was designed to measure. For time-correlated noise, a unified analytical framework incorporating different transformation groups under both quantum and classical interaction is developed and the effect of noise time-correlation is demonstrated. For dynamical decoupling (DD), a family of schemes to suppress noise in the system, we carefully examine the behavior of the periodic-DD (PDD) and the concatenated-DD (CDD) schemes. A rigorous proof for the noise decoupling order of CDD is performed, filling up a logical loophole in previous literature. Together with PDD, we develop a noise threshold condition for the DD schemes with imperfect pulses, shedding light on the appropriate DD scheme to choose from the fault tolerance perspective.