Broadcasting Quantum Coherence via Cloning

Abstract: Quantum coherence (QCh) is considered to be a key ingredient in quantum resource theories and also plays a pivotal role in the design and implementation of various information processing tasks. Consequently, it becomes important for us to create more number coherent quantum states between two labs from a given coherent state shared initially. We call this process as \textbf{Broadcasting of Quantum Coherence (QCh)}. In this work we extensively study the problem of broadcasting of QCh. In order to have a holistic view of broadcasting, we start with a most general representation two qubit mixed state in terms of Bloch vectors. As a cloning transformation we have used universal symmetric optimal Buzek-Hillery (BH) cloner locally as well as non locally. Remarkably, we find that in either of the case it is impossible to do optimal broadcasting of QCh. Further we show in case of non optimal broadcasting it is impossible to increase QCh of the state by both local and non local cloning operations. In non optimal case, apart from general result we consider examples like, a) Werner like states (WLS) and b) Bell diagonal states (BDS) and obtain ranges for broadcasting in terms of input state parameters.