Quantum Coherent Control And Quantum Computation In Solid Systems

In the1980s, the cross development of quantum mechanics, information science and computer science expedited quantum computation and quantum information as an emerging interdiscipline. Quantum computation and quantum information outline the beautiful vision for humanity by break-ing through the limit of classical information science. So far the related research is in the ascendant and tremedous progress have been made both theoretically and experimentally. While deepening the cognition of quantum mechanics itself, abundant achievements benefit from and moreover pro-mote the development of other related disciplines. During the last decade, great efforts have been made to coherently control various physical systems, in order to implement the scalable quantum computation. About the physical realization of quantum computing, different physical systems have respective advantages and bottlenecks. However, with the rapid development of optical technolo-gy, materials science, nanotechnology and superconductivity technology, solid systems including semiconductor quantum dots, nitrogen-vacancy centers and superconducting circuit already have the excellent integratability and controllability, and well stability. Therefore solid systems have be-come the most promising candidates for implementing the scalable quantum computation. In this doctoral dissertation, we focus on the theoretical study of quantum coherent control and quantum computation in solid systems, including the proposals and research of schemes for the coherent con-trol in various solid systems, the expansion and generalization of ceratin existing control schemes, the application of control schemes to the specific quantum information process, and the quantiza-tion and properties of quantum correlation in specific solid systems, etc. The dissertation has been divided into seven chapters, with our own research works contained in the chapters from4to7.In Chapter1, we give a historical overview of quantum computation and quantum information, and introduce the physical conditions and current development situation of the physical implemen-tation of quantum computation. In particular, the research progress of quantum coherent control and quantum computation in solid systems for the past decade are reviewed.In Chapter2, rudimentary knowledge of quantum computation is introduced, including the de-scription of qubits, the concepts of pure states and mixed states, elementary and universal quantum gates, and the definition of fidelity. Moreover, the concept of quantum entanglement and several conventional entanglement measures are introduced.In Chapter3, firstly the morphologies, structure characteristics, and the level structures of2-dimension electron gas quantum dots and self-assembled quantum dots are introduced in detail, respectively. Then several relative traditional schemes for the coherent control of qubits based on solid systems are demonstrated.In Chapter4, we propose a deterministic quantum teleportation protocol of electrons in an array of quantum-dot molecules. The qubit operations are implemented by sequences of stimulated Raman adiabatic passage (STIRAP) pulses. We show the significant efficiency of the protocol:only one c-NOT gate plus one Hadamard gate are required for the basis transformation, and one single-spin rotation for the reconstruction procedure. Picosecond-scale pulses allow for ultra short total duration of the protocol, which is far less than the lifetime of electron spin. After only～5%of the spin coherence time the teleportation process can be completed, which implies a high teleportation fidelity.In Chapter5, the nonadiabatic geometric rotation of an electron spin in a quantum dot by In hyperbolic secant pulses is investigated. The geometric and dynamic phase components of overall phase induced by the pulse are analyzed. The dependence of two phase components on the ratio of the Rabi frequency to the detuning is investigated. Numerical results indicate that only for one resonant pulse the induced overall phase is purely the geometric phase. With other values of the ratio the overall phase consists of a nonzero dynamic part. The effect of spin precession to decrease the dynamic phase is characterized and discussed by analytical and numerical techniques. Utilizing the symmetry relations of the phases, a scheme to eliminate the dynamic phase by multipulse con-trol is proposed. By choosing the proper parameter for each pulse, the dynamic phases induced by different pulses cancel out. The total pure geometric phase varies from-n to n, which realizes the arbitrary geometric rotation of spin. Average fidelity is calculated and the effects of magnetic field and decay of the trion state are compared and discussed. The results show the crucial role of weak magnetic field for high fidelity (above99.3%).In Chapter6, firstly we study the dynamics of quantum coherence and quantum correlations in two semiconductor double-dot molecules separated by a distance and indirectly coupled via a transmission line resonator. Dominant dissipation processes are considered. The numerical results verify the phenomena of entanglement sudden death, entanglement sudden birth, and the robustness of quantum discord to sudden death. Furthermore, the results indicate the dephasing processes in our model can lead in the revival and decay of coherence and discord with the absence of entangle-ment for certain initial states. By observing the dynamics of coherence versus discord for different initial states, we find that the similarity of the behavior results from the close relationship between the nonlocal coherence and quantum correlation. Inspired by this, we thus reexamine quantum cor-relation from the fundamental perspective of its consanguineous quantum property, the coherence. A measure of quantum correlation for arbitrary dimension bipartite states using nonlocal coherence is proposed, and the relationship between consonance and other notions of quantum correlation is investigated.In Chapter7, we develop an architecture of hybrid quantum solid-state processing unit for universal quantum computing. The architecture allows distant and nonidentical solid-state qubits in distinct physical systems to interact and work collaboratively. All the quantum computing pro-cedures are controlled by optical methods using classical fields and cavity QED. Our methods have prominent advantage of the insensitivity to dissipation process benefiting from the virtual excita-tion of subsystems. Moreover, the QND measurements and state transfer for the solid-state qubits are proposed. The architecture opens promising perspectives for implementing scalable quantum computation in a broader sense that different solid-state systems can merge and be integrated into one quantum processor afterwards.Finally, the results are summarized and some prospects are given.