Under Light And Atoms Interacting System. Intrinsic Decoherence Studies

Quantum information science, which mainly includes quantum computer and quantum communication, has increasingly evolved as a new object. Because the carrier of information in this subject is quantum state, all the problems related to information should be resolved by means of quantum theory. Therefore, quantum information science exhibits a number of advantages corresponding to its classical counterpart.With the realization of quantum algorithm and the solution of error avoiding, quantum computing (QC) has attracted many scientists' attention. Based on the properties of quantum superposition and coherence—the essence of quantum mechanics, quantum computing is intended to perform many difficult tasks, which cannot be solved by classical computers. However, as the quantum system is correlated with its external environment, it is very difficult to keep coherence of qubits, which is used in QC. Therefore, many people try to tackle this problem. For example, Milburn gave a simply model of intrinsic decoherence, and made a simply modification to the standard quantum mechanics. Based on this theory, we study some problems following by solving the Milburn equation exactly for the system of two-mode SU (1,1) coherence states and a two-level atom.(1) We investigate the time evolution of the entanglement of field-atom and one of two modes of field using the quantum-reduced entropy and quantum relative entropy, respectively. The influences of intrinsic decoherence and two-mode photon number difference on the evolution of the entanglement of field-atom and one of two modes of field has been discussed. The results show that the entanglement of field-atom reduced to a stationary value with time evolution and the entanglement between two modes increase to another stationary value with intrinsic decoherence, and the values only depend on the two-mode photon number and mean photon number.(2) The effects on the quantum statistical properties of the two-mode SU(1,1) coherent field induced by the intrinsic decoherence, the two-mode photon numberand the mean photon number are analyzed. The results show that the intrinsic decoherence strengthens the anti-bunching effect of the two-mode and the correlation intensity between the two modes and makes the first mode of the field always to be sub-Poissonian. The second-order coherence degree of the two-mode field also exhibits obvious collapse-revival effect with the intrinsic decoherence. The first mode of the field is sub-Poissonian with the evolution of the time. The photon anti-bunching appears and the correlation of the two modes of light is both positive and non-classical. But in most of the time, the second mode of the field is Poissonian with the evolution of the time and the photon bunching appears. The influences of the two- mode photon number and mean photon number on the quantum statistical properties are also very obvious.(3) The effects on the atomic population inversion induced by the intrinsic decoherence, the two-mode photon number and the mean photon number are analyzed. The results show that the collapse and revival phenomena of the atomic population inversion will appear when the two- mode photon number is not zero and will disappear gradually with the decrease of the mean photon number. The collapse and revival phenomena of the atomic population inversion will also appear with the intrinsic decoherence, but the amplitude of the Rabi oscillation will be reduced to zero with the evolution of the time.