Qubit and cavity measurement in circuit quantum electrodynamics

Abstract

Quantum information and computing are rapidly evolving fields that explore and make use of the fundamental quantum mechanical aspects of nature. Applications of these fields are far reaching, and touch the fields of computer science, chemistry and biology. Integral to much of quantum information is the ability to measure a quantum system, and this thesis focuses on novel quantum measurement techniques in superconducting integrated circuits, a leading physical architecture for quantum information. A scalable protocol to read out the state of a superconducting qubit via a coupled microwave cavity and a photon counter is presented. Inspired by this protocol, a protocol is developed for readout of a binary multi-qubit operator, the qubit parity, that overcomes the fundamental limits of previous parity readout schemes. Furthermore, this thesis explores the full quantum description of the state formed when a semi-classical drive is applied to an electromagnetic cavity coupled to a qubit. It is found that this state exhibits novel properties, such as qubit evolution dependent on the cavity-phase, and sets fundamental limits on the accuracy and repeatability of qubit measurement via a cavity. Finally, a protocol is presented to create nonclassical states in an electromagnetic cavity using a nonlinear photon detector, including states for which no preparation technique was previously known.