Theoretic Studies On Quantum Teleportation By Positive Operator-Value Measurement

With the widespread use of classical computers, it is inevitable to suffer from their developing bottle-neck. Under this background, the scientists put forward the idea of "quantum computer", which result in the rapid development of a new subject named quantum information sciences for applying quantum mechanics to denote and manipulate information. As an important branch in quantum information science, quantum teleportation (QT) has been extensively studied and many valuable results have been obtained both in theory and in experiment.In this thesis, we first briefly introduce the background and fundamental principles of quantum information. Then, we review the concept of QT, generation of entangled states, and research progress of QT. Finally, we propose two new schemes for quantum teleportation by the method of positive operator-valued measurement (POVM) and discuss the corresponding success probabilities. In the first scheme, if the sender and the receiver share three bipartite nonmaximally entangled states as quantum channel, we can achieve conclusive teleportion of an arbitrary tripartite state by performing three Bell-state measurements at the sender's side and implementing a proper POVM on auxiliary particles at the receiver's side. Our results show that the successful probability is only determined by the smaller coefficients of the threeinitial entangled pairs. Moreover, the average fidelity of the scheme is better than 2/3 ,which means that the teleportation scheme is superior to the classical communication protocols. In the second scheme, to realize probabilistic controlled teleportation of a two-particle three-dimensional entangled state via POVM, a sender and two receivers share two partially three-dimensional entangled states as quantum channel. It is found that one of the two receivers can recover the original state to be teleported only under the assistance of the other.Our results are useful to understand the relation between the quantum channel and the probability of successful teleportation, and are helpful for investigating the application of quantum teleportation and making a profound research on the process of quantum communication in a sense.