The Manipulation Of Quantum Information And The Protection Of Quantum Entanglement

With the development of modern science, traditional communication technology can’t guarantee the security of communication again, the quantum communication technology appeared. Quantum communication is mainly the process of remote operation of quantum entanglement, and quantum cloning is the process to realize the distribution of quantum entanglement. So generation of quantum entanglement is a basic problem of quantum communication, and quantum cloning is also an important part of quantum communication.At the same time, the quantum entanglement as an important concept in quantum information theory, but also the main resources needed in quantum information processing such as quantum computation, quantum communication. Therefore keep the coherence and entanglement of the quantum system is very important for the actual quantum information processing tasks. However, because of the interaction between the quantum system and environment, the entanglement of the quantum system will inevitably be damaged. So in order to overcome decoherence, people put forward many different programs to protect the quantum entanglement. Weak measurement, as a new measurement method proposed recently, since it was brought forward reflects the widespread application in theoretical physics and experimental physics. One of them is that it can protect the entangled state. However the current study of weak measurements are all in the inertial frames but the real world will inevitably exist rotation and acceleration, treat it as a inertial system is not rigorous. So to solve the problem of entanglement protection under non-inertial frames plays an important role in study the quantum information of non inertial system. This paper presents a systematical research on the manipulation of quantum information and the weak measurement in the non-inertial frames. This paper contains the following results:(1)We propose a scheme for implementing a general quantum cloning machine with distant qubits in a quantum network. First, we introduced the physical model of quantum network. Then we deduced the effective Hamiltonian of this model. We introduced the manufacture process of this cloning machine. By regulating some parameters like times and phases, we can easily realize almost all kinds of quantum cloning machines. At last, we calculated the probability of success of teach project.(2) We study the decoherence caused by environment in a non-inertial frames. It is shown that the decoherence and loss of the entanglement generated by Unruh effect will influence each other remarkably. Then we take weak measurements on each qubits before coupled to a dissipative environment, after all the qubits go into the environment, quantum measurement reversals are applied on each qubits. By calculating the concurrence of the two cases, we find that weak measurement can indeed be useful for combating amplitude damping decoherence and recovering the entanglement of two qubits in noninertial frames. In addition, we select suitable p (weak measurement strength) according to D (magnitude of the decoherence) and acceleration in order to get the best protection effect.(3)We present a scheme to suppress the Hawking effect by using the weak measurements and quantum measurement reversals in the background of a Schwarzschild black hole. It is known that the entanglement is degraded by the Hawking effect with increasing of the Hawking temperature. So before Rob falls toward the black hole, both Alice and Rob are subjected to weak measurements. After Rob falls toward the black hole and hovers outside the event horizon, Alice and Rob carry out quantum measurement reversals operations on the qubits. Then we find that weak measurements and reversing measurements can suppress Hawking radiation effectively. And it has been demonstrated that the success probability decreases as weak measurements strengths increases, and increases as the Hawking temperature increases under constant weak measurements strength.