Optimal Control of Quantum Gates for the NV-center in Diamond

• Main Authors: Yi Chou, 周宜
• Other Authors: Hsi-Sheng Goan
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/77420690029877689607

碩士 === 國立臺灣大學 === 物理研究所 === 101 === The ability to steer a complete set of basis quantum states towards a desired transformation, often referred to as a quantum gate, is one of the essentiality for physical implementation of quantum computing. Many quantum devices are considered and implemented to realize quantum gates. The spin of a nitrogen-vacancy (NV) center in diamond has long coherence times and reliability of quantum operations even at room temperature. Therefore, it becomes a promising candidate for a practical implementation of quantum computing. One of the key challenges now is to overcome the decoherence induced by the uncontrolled couplings to the surrounding environment, preventing high-fidelity gate performance. Optimal control method is one of the effective strategy to dynamically suppress decoherence and to achieve the high-fidelity quantum gates. In this thesis, we first introduce the Krotov optimization method which is one of the most effective and universal computation methods for solving optimal control problems. Then we present the quantum master equation approach for non-Markovian open quantum systems with time-dependent external control. The Krotov based optimal method is then used to implement quantum logical gates for spins of a NV center in diamond, interacting with nearby noise qubits and a Non-Markovian bath. We find the control pulses to achieve high-fidelity X,Z and CNOT gates with errors about 10^{-4} for the NV center.