The Studies On Quantum Correlation Within The Open System

Quantum correlation is an important resource for quantum information processing and quantum communication tasks.However,any open quantum systems are inevitably interacted with the surrounding noise environment,which induces the rapid attenuation and even sudden death of the quantum correlation,namely the quantum decoherence phenomena.Thus,the researches of quantum decoherence phenomena and dynamics behaviors of correlation in open systems,and the accurate understanding of noise environment characteristics and predicting its effects on the quantum system have far-reaching significance on the application of quantum theory.In this paper,we have studied the revival and robustness of quantum correlations and the information flow in open systems.Based on quantum weak and reverse measurement,we proposed some schemes for enhancing the generated quantum correlation in open systems,and provided various entanglement purification schemes in local noise environment.The major results have been listed as follows:(1)We have investigated the dynamics behaviors of quantum correlation and the distribution of entanglement when the single qubit of bipartite quantum system interacts with a local non-Markovian environment.It turns out that the qubit subsystem-environment coupling can induce damped oscillations and revivals for the entanglement,which can gradually decay to a stable value.By analyzing the correlation distribution and the flow of information among all the constituents of the composite system,we have illustrated the non-Markovian mechanisms of these revival behaviors.To gain a quantitative understanding of the information flow,the explicit dynamical relationships among genuine tripartite correlationsv(?ABE),the maximal bipartite correlations imax(?ij)and local state information Iloc(?i)via the methodologies of the corresponding derivatives are revealed,which provides a new insight into the non-Markovian mechanisms during the evolution.(2)We have explored the revival and robustness of Bures distance discord in comparison with entanglement under local nondissipative decoherence.The results showed that considering Bell-diagonal state suffering from decoherence,its quantum correlation will be destroyed with increase of the decoherent to a large extent.Particularly,within depolarizing decoherence channel the distinct difference between them is that Bures distance discord revives after a dark point of time,while concurrence undergoes the sudden death without resurrection.Furthermore,in hybrid decoherence channel we first studied the influences of initial conditions ci(0)on the quantum correlation under the certain noisy environment.With the decrease of c,Bures distance discord damps more smoothly within a limited time,while,beyond the time there is no longer effect on it.However,for concurrence the decreasing parameter c not only.reduces its initial value and also results in an earlier death subjected.In terms of the above results,we derived a fact that Bures distance discord is typically more robust against decoherence than the entanglement.Moreover,when the specific initial state is subjected to the different hybrid channel,the transformations of environments have no effects on concurrence,while it causes several extreme phenomena for Bures distance discord when bit error and bit-phase error occurred with the same probability.For the sake of better insight into these phenomena,we provide a geometric interpretation for Bell-diagonal states.(3)We have investigated the amplitude damping decoherence to generate quantum discord between two separable qubits of an unentangled mixed state by accurately controlling the interaction of qubit with its environment,and then proposed a series of feasible schemes to enhance its sizes by means of weak measurement and reversal measurement.After detailed analysis,the numerical simulations indicated that our enhancing schemes can effectively enhance the size of quantum discord.In this regard,we find that reliable quantum operations can disorder the weight of parts |00>and|11>of initial state,which cause the partial collapse of the input state toward |0>or|1>.In addition,we have obtained the analytic expressions for quantum discord in all of our schemes,and the trade-off relations between success probability and measurement intensity,which entirely depends on measurement strength.(4)By employing weak measurements,we proposed some feasible schemes for purifying two-qubit entanglement in the presence of decoherence.The results showed that as long as measurement strength p and entanglement parameter ? satisfy a certain condition,we can always achieve the purification without reference to the initial state.The success probability of our scheme not only depends on measurement strength,but also closely links to the initial state.