Implementation Of Quantum Phase Gate Based On Semiconductor Quantum Dot-Microcavity Couple System

Quantum computing is a new type of computing which obeys quantum mech-anism, and it aims to realize quantum computer. Quantum logic gate is the basic unit of quantum computer, so it is important for the implementation of quantum logic gate by choosing suitable physical systems. Going along with the rapid de-velopment of semiconductor technology, quantum dot has been widely paid much attention with its extendibility, handleability, and long coherence, which is becoming the most promising candidates in quantum information processing. On the other hand, the construction of multiqubit phase gate is necessary for the implementa-tion of universal quantum computer. Multiqubit phase gate can be obtained with two-qubit controlled-NOT gates and single-qubit gates, however, it requires a lot of auxiliary qubits and operation steps, which not only add the complexity of physical operations, but also squander the quantum resources. Recently, the construction of multiqubit phase gate have been attracting significant attention. Therefore, it has important theoretical value and practical significance for implementing multi-qubit phase gate based on the quantum dot-microcavity couple system. In this dissertation, we mainly do some research as follows:1. We present a scheme for direct implementation of an N-spin qubit controlled phase gate by using quantum dot-microcavity couple system. In the scheme, we first design a quantum entangler device to transform the operated physical qubits into spin-photon non-hybrid entangled states by introducing auxiliary photons. Then we show that, based on this quantum entangler operation, an N-spin qubit controlled phase gate can be probabilistically achieved by the interference and coincidence detection of polarized photons. We discussed the feasibility of our scheme, and the fidelity and the probability of success of the scheme are calculated, showing that the scheme can work in both the weak-coupling and the strong-coupling regime.2. We present a scheme for direct implementation of an N-photon qubit con-trolled phase gate by using quantum dot-microcavity couple system. In the scheme, we first design a probabilistic optical quantum entangler devices to transform the operated physical qubits into two-photon non-maximal entangled states. We can achieve an N-photon qubit controlled phase gate by the interference and coinci-dence detection of polarized photons. Our scheme has the much higher success probabilities of both the quantum encoder circuit and multiqubit controlled phase gate. And the scheme only requires the singlephoton superposition, which greatly saves quantum resources.