量子コンピューティングの台頭

タイトル: Quantum information processing with superconducting circuits: realizing and characterizing quantum gates and algorithms in open quantum systems

概要: This thesis focuses on quantum information processing using the superconducting device, especially, on realizing quantum gates and algorithms in open quantum systems. Such a device is constructed by transmon-type superconducting qubits coupled to a superconducting resonator. For the realization of quantum gates and algorithms, a one-step approach is used. We suggest faster and more efficient schemes for realizing $X$-rotation and entangling gates for two and three qubits. During these operations, the resonator photon number is canceled owing to the strong microwave field added. They do not require the resonator to be initially prepared in the vacuum state and the scheme is insensitive to resonator decay. Furthermore, the robustness of these operations is demonstrated by including the effect of the decoherence of transmon systems and the resonator decay in a master equation, and as a result, high fidelity will be achieved in quantum simulation. In addition, using the implemented x-rotation gates as well as the phase gates, we present an alternative way for implementing Grover's algorithm for two and three qubits, which does not require a series of single gates. As well, we also demonstrate by a numerical simulation the use of quantum process tomography to fully characterize the performance of a single-shot entangling gate for two and three qubits and obtain process fidelities greater than 0.93. These gates are used to create Bell and Greenberger-Horne-Zeilinger (GHZ) entangled states.