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خصائص نقل الالكترون لكيوبت مقترن بترانزستور الالكترون المفرد == The Electron Transport Properties of Qubit Coupled with SET
Author name:
ايات طاهر ابراهيم
Supervisor name:
جنان مجيد المخ
General topic:
Physics
Specific topic:
Electronics Physics
Degree:
Master
University:
University Of Basrah - College Of Education For Pure Sciences - Department Of Laser Physics
Language:
Arabic
University location:
Basrah
First pages:
26T1667 - p.pdf
Abstract:
In this work, the dynamics of electron transport through a system consists of qubit (two coupled quantum dots) electrostatically coupled with single - electron transistor (quantum dot coupled to leads). The time - dependent Hamiltonian, that is used to describe the system energy, includes the electrostatic coupling between the qubit and the single - electron transistor. The time - dependent equations of motion for all the creation and annihilation operators are expressed in Heisenberg representation to derive the differential equations of motion for the quantum dots occupation numbers of the qubit and the single electron transistor, the related equations of motion for the correlation functions and also the formula that calculates the current which tunnels from the left lead to the single - electron transistor quantum dot. The system of equations of motion are treated by using the wide band approximation, and are solved numerically by using six order Runge - Kutta method, where the error is calculated at each step of time. By getting use of the system of differential equations solutions, the qubit and the single - electron transistor quantum dots occupation numbers are calculated as a function of time, in addition to the current that tunnels from the left lead to the single electron transistor quantum dot as a function of time.The main goal of this study in to investigate the effect of the parameters that related to the qubit and the single - electron transistor and their role in determing the electron transport process features through the whole system. These parameters, that are related to the initialization, manipulation and measurement processes, are the qubit and the single electron transistor quantum dots energy levels, the coupling strength between the qubit quantum dots, the electrostatic coupling between thequbit and the single electron transistor in addition to the coupling strength between the single - electron transistor quantum dot and the leads as well as the leads properties such as tempreture and band width. The effects of quantum dots energy levels tuning and the symmetry of the coupling with leads on the electron transport through the system are also investigated.Our study highlights four important physical features that related to the initialization, manipulation and measurement processes, these are : 1. The occupation numbers of the quantum dots of the qubit and the single electron transistor and the current of SET at the final time of measurement.2. The charge accumulation on the qubit quantum dots, at the final time of measurement, on the far - removed quantum dot and the nearest one to the single - electron transistor, that can be controlled by appling bias voltage and gate voltage.3. The determination of the time - current dependence if it follows the dependence of the far - removed or the nearest qubit quantum dot occupation number on time.4. The role of qubit energy levels tunning and the asymmetric coupling with the leads in determining the suitable initialization and manipulation processes get the quantum measurement with high quantum efficiency.
