Entropic Uncertainty And Quantum Discord In Two Two-level Systems In Dissipative Environments

The uncertainty principle,which bounds the uncertainties involved in obtaining precise outcomes for two complementary variables defining a quantum particle,is a fundamental principles in quantum mechanics.The fact that for certain pairs of observables the outcomes of a measurement cannot both be fixed with an arbitrary precision has led to many physical and philosophical discussions.There are different mathematical forms of the physical content of uncertainty relations:In addition to the Heisenberg uncertainty relation in which variance is used to express the uncertainty of measuring quantum fluctuations,there is another entropy uncertainty relation in which entropy is used to express the uncertainty of measuring quantum fluctuations.Recently,the uncertainty principle in terms of entropy has been extended to the case involving quantum entanglement,the uncertainty is shown to be near zero in the presence of quasi-maximal entanglement.In recent years,the studies of entropic uncertainty has been helpful for witnessing entanglement and in establishing the security of quantum key distribution.Quantum discord is a measure of quantum correlation which is different from quantum entanglement.It is of great significance in quantum computation and quantum information field to characterize the relationship among quantum states.In reality,a quantum object is susceptible to its surrounding environment,which will inevitably result in decoherence or a dissipative effect of the system concerned and thus increases system's entropic uncertainty.With this in mind,it is of fundamental importance to make it clear how diverse decoherence affects the entropic uncertainty and quantum discord in dissipative environments.In this paper,we introduce a dissipative ancilla system to control entropy uncertainty and quantum discord in two two-level systems,and obtain some innovative results.The specific contents and research results are as follows:In Chapter 2,a brief introduction of the basic theory of uncertainty relation and quantum discord,and then quantum discord and classical correlation can tighten the uncertainty principle in the presence of quantum memory.Finally,the basic theory of open system and the Markovian master equation are introduced.In Chapter 3,the control of the entropic uncertainty and quantum discord in two two-level systems by an ancilla in dissipative environment is studied.The results show that,the entropic uncertainty of observed system can be reduced and the quantum discord between observed system and quantum memory system can be enhanced by adding an dissipative ancilla with appropriate parameters.Furthermore,we present an effective strategy to further reduce the the entropic uncertainty and enhance the the quantum discord via quantum-jump-based feedback control.In Chapter 4,The entropy uncertainty of the measured system when the twoqubit system and the plasmonic nanoantennas are modulated periodically at zero temperature.The results show that,the coupling of plasmonic nanoantenna to the qubits can reduce entropic uncertainty,the rotating-wave term is a major role in reducing entropic uncertainty In the case of resonance.However,the coupling strength between the driving field and the nanoantenna can not reduce entropic uncertainty.What is more,In the case of non resonance,When qubits symmetrically coupled to a nanoantenna,quantum states with zero entropic uncertainty can be prepared by an antisymmetry in the transition frequencies of the qubits.In Chapter 5,a conclusion and prospect are presented.