Study of the decoherence of a double quantum dot charge qubit via the Redfield equation.pdf

Study of the decoherence of a double quantum dot charge qubit via the Redfield equation Zeng-Zhao Li, Xiao-Yin Pan, Xian-Ting Liang∗ Department of Physics and Institute of Modern Physics, Ningbo University, Ningbo 315211, China 8 0 0 2 l u J 0 2 ] h p - t n a u q [ 1 v 1 4 1 3 . 7 0 8 0 : v i X r a 1 Abstract By using the Redfield form of the master equation, we investigate the decoherence times of a double quantum dot charge qubit (DQDCQ) in three different cases, namely when it is coupled to (I) the piezoelectric coupling phonon bath (PCPB), (II) the deformation coupling phonon bath (DCPB), and (III) the Ohmic bath. It is found that our results for case (I) and (II) are in the same magnitude with those obtained via the exact path integral methods, while for case (III), the decoherence time is in well agreement with the experimental value. Keywords: Quantum dot; Decoherence; Redfield equation PACS numbers: 73.63.Kv, 03.65.Yz, 03.67.Lx I. INTRODUCTION The double quantum dot (DQD) charge qubit [1-5] is one of the qubits that are considered to be promising candidates for the realization of the building blocks of quantum information processing. Its two low-energy states are denoted as the local states |0 and |1, which could be controlled via external voltage sources. There exist some effective schemes to prepare the initial states and readout the final states of the qubit [6]. It is also known that this kind of qubit is coupled to its environment inevitably. Therefore, it is believed that the decoherence might be the central impediment for the qubit to be taken as the cell of quantum computer. He