Quantum Information Processing Based On Quantum-dot Spin And Cavity Quantum Electrodynamics

Based on the basic principles of quantum mechanics and the unique properties of the quantum state,the development of information technology has entered a new stage,and safe and high-speed quantum information processing has become a research hotspot in the world.The challenges of the physical implementation of quantum information processing in terms of scalability,operational complexity,noise suppression ability,and integration are the core bottlenecks in the realization of large-scale general-purpose quantum computing and quantum information networks.Quantum logic gates manipulate and transform quantum states,which are the core components of quantum information processing.The combination of single-qubit logic gates and two-qubit Controlled-NOT gates(CNOT gates)can realize any-qubit quantum computation,so the construction of quantum CNOT gates has attracted extensive attention.In addition,the development of more direct and effective methods to construct other multi-qubit logic gates,which can reduce the complexity of quantum circuits,has also received extensive attention.Therefore,the construction of high-fidelity and high-efficiency two-qubit and multi-qubit universal quantum logic gates is of great significance for the realization of large-scale quantum information processing.Based on the spin confined in the quantum dot and cavity quantum electrodynamics,the thesis carried out theoretical research on the construction of quantum logic gates and quantum information processing and achieved some significant results:First,based on the giant circular birefringence(GCB)induced by a singleelectron spin confined in a quantum dot inside a single-sided optical microcavity,the schemes implement a three-qubit Toffoli gate and a three-qubit Fredkin gate on a two-photon system are proposed.For the three-qubit Toffoli gate,the two control qubits are encoded on the polarization and spatial mode of the control photon,respectively,and the target qubit encoded on the polarization mode of the target photon.For the three-qubit Fredkin gate,the control qubit is encoded on the polarization mode of the control photon,and the two target qubits are encoded on the polarization and spatial mode of the target photon,respectively.Utilizing the two Degrees of Freedom(DoFs)of photons for encoding,the proposed schemes can reduce the photon consumption,facilitates the storage of quantum information,and be more robust against the photon loss and decoherence caused by the environment.Second,the balance condition theory for the photon scattering process assisted by microcavity is developed.Utilizing the single-photon input-output process in the single-sided QD-cavity systems under the balance condition,a two-qubit quantum CNOT gate and a three-bit quantum Toffoli gate on spin systems are proposed,which can realize high-fidelity and scalable solid-state quantum computation.In addition,high fidelity universal two-qubit CNOT gate,three-qubit Toffoli gate,and three-qubit Fredkin gate are proposed on hybrid quantum systems,which consists of flying photons and QD-confined electron spins.The schemes have the advantages of scalability and are more suitable for quantum networks.The noise introduced by unbalanced reflectance between the coupled and uncoupled QD-cavity systems can be effectively suppressed by the construction of balance condition,hence the fidelity of the logic gate can be increased to unity in principle.In addition,the realization of the balance condition does not require the QD-cavity system to work in the strict strong coupling regime,which makes the theoretical scheme more feasible.Third,employing single-sided QD-cavities and linear optical elements,the heralded error-reject operation units are constructed.The units can predict the success of the quantum operation and transform the errors introduced by weak coupling strength,frequency detuning,and imperfect photon scattering into the heralded photon loss,thus avoiding adverse effects on the fidelity of quantum operation.The modular design of the heralded error-reject operation units makes the circuits more concise and has good flexibility and expansibility.Using the units five hyper-parallel quantum CNOT gate schemes for twophoton systems are proposed,covering all five cases in which the polarization and spatial mode of the photon system are simultaneously involved in the evolution.In addition,a parallel transmission scheme of nonlocal quantum CNOT gates between two remote quantum network nodes is proposed.With the help of heralded error-reject operation units,the fi delity of these quantum gates can reach unity in principle.The parameter requirements of Cavity Quantum Electrodynamics(Cavity-QED)are relatively loose,which reduces the difficulty of the experiment.In addition,the nonlocal CNOT gate scheme uses hyperentanglement to establish quantum channels,and the parallel transmission of two CNOT gates improves the computational speed,which is promising for realizing quantum networks with high channel capacity.The calculation results show that the above schemes have good performance under the current experimental conditions,which can effectively resist the influence of noise,have high fidelity,and are resource-effective schemes,reducing the experimental complexity.With strong practicability and scalability,it can be applied to large-scale quantum information processing and the construction of quantum networks.Among them,quantum gates on spins can be used for solid-state scalable quantum computation,hyper-CNOT gates can further improve the speed of parallel computation.The hybrid quantum gates and nonlocal quantum gates can be used to build quantum networks for further developing the capacity of quantum information transmission and processing.These work advances the realization process of large-scale quantum information processing and quantum network construction.