Analysis of Local Operations Influence on the Entanglement of Two-Qubit States
Nina Sukhodoeva, Zhaofeng Su · 2024
Entanglement is a remarkable phenomenon observed in quantum systems, which has many potential applications in the field of computing, communications and cryptography. In quantum information theory, entanglement is considered as an indispensable resource that can be quantified and purified. In typical quantum information task, a quantum state is distributed between two spatially separated observers that can only perform operations on their part of quantum system. In this scenario, the possibility of increasing amount of entanglement is of practical importance. In this paper we investigate the increase of quantum entanglement that can be achieved by local operations for 2-qubit states. Firstly, we employ the formula for the concurrence change under local operations to analyze the possibility of entanglement increase for a pair of local operations depending on the parameters of operators and the state. Secondly, we evaluate the expectation value of the concurrence under a set of local operations performed by one and two observers. Finally, we consider two classes of density matrices under stochastic local operations and classical communication.