Two-level atoms act as qubits in quantum computing. They are widely used for storing quantum information. According to the principles of quantum computing, the evolution of quantum cell states must be a unitary transformation. This requires us to be able to completely make quantum memory cells complete. Isolated in the macro environment, but in reality the quantum storage unit is not isolated from the outside world, it is always in a certain external environment. There is always some interaction between quantum memory cells and the environment, which will make the evolution of the state of the quantum memory cells not a unitary transformation, resulting in erroneous calculation results. This phenomenon is called decoherence>6 for two-level atoms In general, the dynamic properties of the thermal storage have been studied using Markoff's approximation. The principal equations and reduced density matrix in a thermal library with two-level atoms at any temperature have been deduced. The single-photon process for dequeuing qubits has been discussed. In the actual process of impact, we hope that we can artificially prepare the library to study the dynamic characteristics of the quantum storage unit in the library. This idea is achievable. Since the experimental success of the compressed vacuum state, Gardinei. The idea of ​​atoms immersed in a compressed vacuum field. This library of multi-mode compressed vacuum fields is often referred to as an artificially prepared library. From this we can see that the artificially prepared library differs greatly from the general thermal library, especially in the degenerate two-photon process. This paper presents the Markoff property in the paper. In this paper, we use the perturbation theory to iterate equation (5) to d(t). In the case of the second order of the terms, the library's density operator is not coupled to the library due to the initial time quantum memory cell and library, and it can be considered that Hi(t) and d are commensurate, that is, (6)=0, and the quantum memory cell reduced density calculation is assumed. The symbol is dqi(t). If the library is large, although the density operator of the entire system changes with time when the library is coupled with the quantum storage unit, it can be considered that the library has not changed. At this time, it can be approximated and considered as di (t produces d ( t) At this point, Equation (8) becomes available for a compression vacuum library, and V 01 indicates that the memory cells are in a low energy state, and if df=, then there are four matrix elements. The decoherence of the quantum memory cells can be achieved by The density operators non-diagonal elements are reflected over time, so we mainly consider 'd.' to further determine the changing law of d01d10 over time and use SI1>=0 and their conjugate vectors (left vectors). ) is available.
2.2 Degenerate two-photon process For the quantum memory cell and the compressed vacuum library through the degenerate two-photon interaction, the Hamiltonian of the system is the reduced density operator of the quantum memory cell as the natural decay constant. Using the same method of processing single photon processes, we can obtain the natural decay of atoms in the process of single photon 1 (the decoherence property of the number of total 3 quantum memory cells. Since we only need to study the evolution law of non-diagonal elements of the density matrix, we can In the degenerate two-photon process, simultaneous equations 18) and 19) are solved.
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