Quantum optimal control for quantum information processing
Hsi-Sheng Goan1,2*
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Center for Quantum Science and Engineering, National Taiwan University, Taipei, Taiwan
* presenting author:Hsi-Sheng Goan, email:goan@phys.ntu.edu.tw
An essential prerequisite for quantum information processing (QIP) is precise coherent control of the dynamics of quantum systems or quantum bits (qubits). Most of the control sequences implemented in quantum experiments are developed and designed based on the assumption of having ideal (closed) quantum coherent systems. However, almost every quantum system interacts inevitably with its surrounding environment resulting in decoherence and dissipation of the quantum system. Thus precisely controlling realistic open quantum systems is one of the most important and timely issues in the field of QIP. Here we employ Quantum optimal control theory (QOCT) based on the Krotov method to find control pulse sequences of fast and high-fidelity quantum gates taking into account decoherence from dissipative environment for various promising physical quantum systems, such as NV-center-based spin-qubit systems and superconducting Josephson-junction-based qubit systems. Furthermore, we also apply QOCT to some exactly solvable models of non-Markovian open quantum bit systems to achieve and construct high-fidelity quantum gates. Despite the broad applicability of the perturbative master equation, the approximations made in the derivation results in unwanted intrinsic error, which in turn contributes to the error in the constructed gate operations. With the help of the exact dynamics, we explore how the gate error is corrected in the open qubit system and determine the conditions for significant improvement.

Keywords: Quantum control, Quantum gates, Quantum computing, Open quantum system