Quantum State Generation And Logic Gate Implementation Using Solid Devices

The solid quantum devices are particularly appealing and have been consid-ered as one of promising physical systems for quantum computation. This paper will mainly focus on the quantum state generation and the logic gate construction with superconducting qubits and NV centers in quantum information processing. This paper is organized as five chapters:In chapter 1, we introduce research background and development of solid-state qubits, and introduce our research results.In chapter 2, we introduce the basic notions in quantum optics and quantum informations, and basic knowledge used in our research works.In chapter 3, we propose a way to generate a macroscopic W-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cav-ity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which should significantly reduce its experimental diffi-culty. For most of the operation time, each cavity remains in a vacuum state, thus decoherence caused by the cavity decay and the unwanted inter-cavity crosstalk are greatly suppressed. Moreover, only one external-cavity coupler qubit is need-ed. This method is quite general and can be applied to generate the proposed W state with atomic ensembles or other spin ensembles distributed in different cavities.In chapter 4, we present a simple and efficient scheme for realizing a multi-target-qubit unconventional geometric phase gate in a multi-cavity system. This multiqubit phase gate has a common control qubit but different target qubits dis-tributed in different cavities, which can be achieved using a single-step operation. The gate operation time is independent of the number of qubits and only two lev-els for each qubit are needed. This multiqubit gate is generic, e.g., by performing single-qubit operations, it can be converted into two types of significant multi-target-qubit phase gates useful in quantum information processing. The proposal is quite general, which can be used to accomplish the same task for a general type of qubits such as atoms, NV centers, quantum dots, and superconducting qubits.In chapter 5, we present the conclusion and discuss the outlooks.