The Pure Dephasing Due To Longitudinal Acoustic Phonons For Exciton Qubit

In a quantum dot (QD), the electronic ground state and the lowest-energy exciton state may be employed as a two-level quantum system– qubit. This paper calculates pure dephasing due to deformation potential exciton-bulk longitudinal acoustic phonons (LAP) interaction for exciton qubitFirst of all, the pure dephasing due to deformation potential exciton-bulk LAP interaction for exciton qubit is calculated by using the reduced density matrix in a spherical QD. The dependence of dephasing factor on time and the confinement length of the QD and temperature is discussed. The study finds the pure dephasing factor increases with increasing time quickly when time is smaller than 2.5 ps, pure dephasing time is in the order of ps; Even at absolute zero temperature, exciton-LAP interaction still cause excitonic dephasing, the pure dephasing factor increases with increasing temperature quickly when temperature is bigger than 5 K. In the same time, the confinement length of the QD has important effects on pure dephasing of qubit, the quantum size is more small, pure dephasing is more quick.Then, the paper investigates the pure dephasing due to deformation potential exciton-bulk LAP interaction for exciton qubits under the influence of external static electric and magnetic fields by adopting the full quantum-mechanical method of Kunihiro Kojima and Akihisa Tomita in a two-dimensional QD with parabolic confinement potential. The wave–function is found and the dependence of the pure dephasing factor on the confinement length of the QD and time and temperature is discussed under the external static electric and magnetic fields. The study finds the pure dephasing factor increases quickly in the first 1.5 ps for different electric field strengths and magnetic field strengths. At higher temperature, the influences of external static electric and magnetic fields can not be neglected, and strong static electric or strong magnetic field leads to obvious pure dephasing. At the same time, the study finds the influence of static magnetics field on bigger QDs is greater than on smaller QDs. For static electrical fields, the influence of weaker static electric fields on bigger QDs is obvious and the influence of stronger static electric fields on smaller QDs is obvious.