Study Of Transport Properties And Decoherence Mechanics In Mesoscopic Systems

The more improvement of the computer technology, the higher requestment for micro-electronics technics. Today Intel Cornpany has achieved the 0.09 micron machining for it's CPU and will carry out the nano-machining soon. Quantum effects such as strongly correlation will be emerged in the nano-machining electrocircuits in which the ohm-law is invalid and therefore information technology will encounter to an insurmountable obstacle.To get across the obstacle of quantum effects, there are two roads to choice for us: One way is that we continue to research the electronic transport law in nano-machining electrocircuits, which can contain the quantum effects. Another way is that we give up the classical computation schemes and seek bran-new compute scheme—quantum computation schemes.In this paper, we carry through some investigations based on above-mentioned two aspects. In the first chapter, we introduce an especial physics effect: Kondo effect, which is premised for the latter chapters. In the second chapter, using cluster expansions method (which improved by correlation dynamics) to research the transport properties of quantum dots, we have calculated the Kondo effect in electronic transport conductance. In the third chapter, the Fano effect is calculated by Green's function method under Lacroix's approximation and a peculiar phenomenon that Fano effect suppresses Kondo effect is found by theoretical calculation. In the fourth chapter, we introduce the decoherence mechanics of the Kondo singlet and propose that phase shift measure is a kind of decoherence mechanics of the Kondo singlet. In the fifth chapter, a single qubit gate is realized by laser-two-level-atom system and the decoherence process of this system is discussed in detail.Innovation of this paper lies in five aspect: First, using cluster expansions method (which improved by correlation dynamics) to research the transport properties of quantum dots, we have calculated the differential conductance curve in which the narrow peak manifests itself as the Kondo effect consistent with the experimental observation. Second, the transport properties of Aharonov-Bohm interferometer coupling to a quantum dot are calculated by Green's function method under Lacroix's approximation and a peculiar phenomenon that Fano effect suppresses Kondo effect is found by theoretical calculation. Third, through analyzing the diversity of the Kondo effect among quantum dot model, Aharonov-Bohm interferometer coupling to a quantum dot model and quantum point contact (QPC) model, we point out that phase shift detection is a kind of the mechanism of decoherence of the Kondo singlet. Forth, a single qubit gate is realized by laser-two-level-atom system using algebraic dynamics method. Fifth, since any quantum logical gate must overcome the decoherence problem, the decoherence process of this system is discussed in detail under the Markovian's approximation. We also discuss the comeback process of the coherence of laser-two-level-atom system under Markovian quantum feedback. The investigation of this paper has deepened the comprehension of mesoscopic transport properties and decoherence mechanics of the Kondo singlet, and expanded the understanding of the decoherence process of a single qubit. We have expressed some significative results in this paper.