Quantum Information In Double Quantum Dots

This dissertation conducts several important quantum information processes in semiconductor quantum dots. Semiconductor quantum dots is one of the solid-state devices which are most capable to build quantum computer. It can be accessed and scaled more easily, and has a long coherence time. By encoding qubits on electron spins in quantum dots, for example single electron spin up and down, or two-electron spin singlet state and triplet state, we can research many kinds of quantum information processes. In this dissertation, our work focuses on using quantum double-dot systems to realize quantum computation. The main content and characteristics of this dissertation are listed as follows:1. First, this thesis introduces the background and motivation of the research about semiconductor quantum dots. We concretely introduce the structure of quantum dots, and how to encode qubits on electron spins in quantum dots for quantum computation.2. We introduce a double quantum dot structure without two-qubit interactions, which can be used to realize the measurement-based quantum computation. Based on this structure, we propose to complete the quantum non-demolition Bell-state measurement, and further prepare n-party GHZ state which can be used to realize quantum computation.3. We detailedly discuss the coupled double-dot structure (quantum double dot molecular), and table two proposal for quantum computation based on it. One way is using double quantum dot molecule chain to generate cluster state. Combining cluster state with single qubit operation and readout, we can realize quantum computation. In another way, we use double quantum dot molecules to construct universal gate, and then quantum computation can also be performed.4. In order to increase the interaction strength between two double quantum dot molecules, we propose to use a superconducting transmission line resonator (TLR) to connect many double quantum dot molecules. In our scheme, qubits are biased at the large detuning region, and thus the decoherence mechanism of the cavity loss can be effectively suppressed.5. Combining theory with present experimental conditions, we discuss quantum computation based on double quantum dot structure in detail, and give aview about future work.The main innovation results of this dissertation:1. We give a proposal about non-demolition Bell-state measurement based ondouble quantum dot structure without two-qubit interaction, and the double quantum dot molecular system can be run under the nonadiabatic condition. This idea about non-demolition Bell-state measurement can be used to prepare n-party GHZ state, and then quantum computation can be realized.2. We propose to arrange many double quantum dots as a chain: the two dots inside each molecule are perpendicular to the qubit scaling line. This structure greatly simplify the interaction between two nearest-neighbor qubits (as a Ising model), and can generate the cluster state by one step. This simplified interaction can create two-qubit and realize Bell-state measurement. Further, this arrangement is good for spread and we can expand it into two- dimensional logic qubit space.3. In our scheme of double quantum dot molecular chain, we can effectively eliminate the influence of the interaction between non-nearest-neighbor qubits through calculating.4. We propose to couple double quantum dot molecules with a transmission line resonator (TLR), and thus the coupling strength between two double quantum dot molecules can be much enlarged (the direct coulomb interaction is not large enough). This model is a multi-qubit model, and through TLR we can choose any two double quantum dot molecules to perform two-qubit operation. Futhermore, we propose to put qubit operation in the dispersive coupling regime, and in this way we can decrease the decoherence induced by cavity loss.