Enhancing the Fidelity of Controlled Quantum Teleportation by Multi-Qubit Entangled State

Due to the coupling with the noisy environment, the quantum state in the target quantum communication system will undergo decoherence and reduce the fidelity. To diminish the noise effect, we utilized weak measurement (WM) and weak measurement reversal (MWR) to enhance the fidelity of controlled quantum teleportation (CQT). The CQT protocol was first proposed, in which Alice prepared an eight-qubit entangled state as a quantum channel. With controller Bob's permission, an arbitrary two-qubit state can be transmitted to Charlie. Then We extend the CQT protocol for an arbitrary two-qubit state to an unknown 2N-qubit state. Then we separately analyzed that the two CQT protocols process were influenced by amplitude damping (AD) noise, leading to an inevitable reduction in its fidelity. In both cases, WM and WMR operations respectively were performed before and after undergoing the noise channel. Our results showed that the fidelity of transmitting the two-qubit state with two measurement operations is improved, which can hold true in the entire evolutionary field. However, when N is greater than 1, the fidelity of transmitting the 2N-qubit state does not always increase with WM and WMR operations but will be lower than without those operations in a certain value range of noise factor and weak measurement strength.