| Quantum dot, which is a quantum confinement system in all three dimensions, is one of the most promising candidates for quantum computer. In this thesis, we perfomed the transport experiment and simulation to study the properties of the GaAs/AlGaAs double quantum dots system at low temperature. We observed a continuous transition from a separated two electron states exhibiting a square structure to a coupled two electron states exhibiting a honeycomb structure by increasing the inter-dot coupling. Furthermore, using the Rabi oscillations and LZS interferences, a shaped electrical pulse was applied to drive the charge qubit formed by quantum dots.Following are the main content of this thesis:1. Introduced the principle of the gates defined quantum dot after described the2D electron gas. We also introduced the CI model and some key concepts and phenomenons, including electrical potential, charge energy, Coloumb diamond, cotunneling, and so on.2. Taking the series double quantum dot for example, we described the charging stability diagrams, the formula of coupling strength and charge energy.3. Introduced some equipment which was used in nano-fabircation, such as MJB3, SEM, and so on. We also described the processes of the nano-fabrication and gave the description of the measurement at room temperature and4.2K.4. We probed the electron states on lateral double quantum dots coupled in parallel. The charge stability is given in terms of the electrochemical potentials of both dots. We realize the two electron states from separated states to coupled states continuously by increasing the inter-dot gates voltage.5. We proposed an effective method to design the working parameters of a pulse-driven charge qubit implemented with double quantum dot. It is shown that intrinsic qubit population leakage to undesired states in the control and measurement process can be determined by the simulation of coherent dynamics of the qubit and minimized by choosing proper working parameters such as pulse shape. 6. We studyed the dynamic behavior of a two-level system with time varying detunings in double quantum dots. Two Limiting cases were considered:Rabi oscillations and LZS interference. The LZS interference fringes have been observed in charge stability diagram, in time domain, and in pulse amplitude space of the driven pulse. Following are the main innovations of this thesis:1. We performed the transport experiment on parallel two quantum dots to probe the electron states. A continuous transition from separated two electron states to a coupled two electron states can be observed in the charge stability diagrams. Precision control of the number of electrons in the coupled quantum dot system provides a promising environment for the development of quantum information processing.2. We performed the simulation to probe pulse controlled coherent dynamics of the qubit. The efficiency of our approach are demonstrated by applying it to optimize the working parameters, such as pulse profiles, for high-fidelity one qubit coherent dynamics in the presence of intrinsic leakage. More importantly, our protocol is quite robust in the improvement of more complicated gate performances which bodes well for future quantum information studies.3. We observed Rabi oscillations of a pulse-driven charge qubit in series coupling double quantum dots system. Our data demonstrated that the charge qubit in semiconductor quantum dot can be closely controlled and the charge qubit bodes well for future quantum computing applications.4. A very fast dynamic phase rotation of several pico-seconds has been accomplished. The characteristic anti-crossing and the quantum phase coherence of the qubit have also been obtained by perfoming the amplitude spectroscopy. We envision that very fast universal gate operations, on orders of50ps, can be carried out in a semiconductor charge qubit by employing the combination of non-adiabatic Rabi oscillation excitation and the LZS interference, as described here, with a set of electrical pulses. |
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