| Quantum information science is a new subject which is produced by the combination of quantum mechanics and information science,so it has many characteristics that classical information science does not have,such as quantum coherence,quantum entanglement,quantum state superposition principle and so on.With the development of quantum informatics,it is found that many tasks which cannot be accomplished by classical information can be accomplished by using these characteristics.,therefore quantum coherence plays a very important role in quantum information processing tasks.But unlike classical informatics,quantum informatics stores information in the quantum states of microscopic particles,due to the existence of the surrounding environment,in the process of quantum information transmission,the quantum state cannot be avoided interact with the noise environment,resulting in the generation of the decoherence effect,and this decoherence effect has irreversible damage to the quantum entanglement.In order to effectively suppress the influence of the environment on the quantum system,we first need to understand the interaction process between the environment and the quantum system,and then study how to suppress the influence of the environment on the characteristics of the quantum system.In recent years,quantum Fisher information(QFI)has attracted considerable attention due to its importance in quantum estimation theory and its connection with the rapid development of quantum metrology.Quantum Fisher information is mainly used to measure how much parameter information is carried in a group of random variables containing parameters,and it gives a lower limit to determine the measurement accuracy of parameters mathematically.However,the quantum Fisher information is very sensitive to noise environment,which will lead to the decrease of measurement accuracy.Therefore,this paper mainly studies how to suppress the generation of decoherence effect and how to improve the quantum Fisher information.(1)The interaction between atoms and cavity field and the dynamic evolution of quantum coherenceOn the basis of the knowledge of quantum coherence and open quantum system,we select two identical atoms a and b with two energy levels,the dynamic evolution of quantum coherence and the interaction between atoms and single-mode cavity field under two different conditions are investigated.Since the constraint condition of measuring coherence has been put forward,many methods of measuring quantum coherence have been proposed one after another,in this paper,a simple L1 norm is used to measure the quantum coherence of the system.It is found that in the case of large detuning,the inhibitory effect on the decoherence effect is better than that on the resonance effect,and when quantum system is in the maximum entangled state,the quantum coherence of the system remains at the maximum value of 1 in the case of large detuning.Therefore,a large number of quantum information processing schemes can be designed according to the characteristics of the cavity field.(2)The filtering measurement operation is used to increase the action of quantum Fisher information under the amplitude damped channel(AD).The quantum Fisher information of quantum states with weighted parameter and phase parameter under the action of amplitude damped channel is studied.The results show that the quantum Fisher information of both the weight parameter and the phase parameter will decay with the increase of the damping rate of the amplitude-damped channel.In addition,the symmetry of the quantum Fisher information function of phase parameter is broken due to the influence of the amplitude damped channel.Due to the filtering measurement operation has the probability of bringing the quantum state back to the state before the measurement,therefore,we propose a scheme to improve quantum Fisher information by filtering measurement operations,and it turns out that filtering measurement operations can improve quantum Fisher information. |
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