Abstract

In this work, we extensively study the problem of broadcasting of quantum correlations (QCs). This includes broadcasting of quantum entanglement as well as correlations that go beyond the notion of entanglement (QCsbE). It is quite well known from the “no-broadcasting theorem” that perfect broadcasting of QCs is not possible. However, it does not rule out the possibility of partial broadcasting of QCs where we can get lesser correlated states from a given correlated state. In order to have a holistic view of broadcasting, we investigate this problem by starting with a most general representation of two qubit mixed states in terms of the Bloch vectors. As a cloning transformation we have used universal symmetric optimal Buzek-Hillery (BH) cloner both locally and nonlocally. Unlike entanglement, we find that it is impossible to broadcast QCsbE optimally. Lastly, we generalize these results for any symmetric or asymmetric cloning machines as well. This result brings out a fundamental difference between the correlations defined from the perspective of entanglement and the correlations measure which claims to go beyond entanglement.

Abstract

It often happens in quantum information processing that we are given an entangled pair and asked to create more entangled pairs by using local quantum operations. This need arises from the fact that sometimes there is more priority on increasing number of participants in information processing scheme rather than on the efficiency of it. To address this we consider a 2⊗ 2 dimensional system and apply optimal universal quantum cloner to create more entangled pairs. Then we analyze the dependence of maximal fidelity of teleportation and super dense coding capacity on broadcasting and cloning fidelities. Since the amount of quantum correlation, namely entanglement and discord, between the participating subsystems play a vital role in the efficiency of information processing schemes, we further study the dependence of these quantum correlations, on broadcasting and cloning fidelities.

Abstract

In this work we consider a quantum network consisting of nodes and entangled states connecting them. In every node there is a single player. The players at the intermediate nodes carry out measurements to produce an entangled state between the initial and final node. Here we address the problem that how much classical as well as quantum information can be sent from initial node to final node. In this context, we present strong theorems which state that how the teleportation capability of this remotely prepared state is linked up with the fidelities of teleportation of the resource states. Similarly, we analyze the super dense coding capacity of this remotely prepared state in terms of the capacities of the resource entangled states. However, we first obtain the relations involving the amount of entanglement of the resource states with the final state in terms concurrence. These relations are quite similar to the bounds obtained in references [G. Gour, Phys. Rev. A 71, 012318 (2005); G. Gour, B.C. Sanders, Phys. Rev. Lett. 93, 260501 (2005)]. More specifically, in an arbitrary quantum network when two nodes are not connected, our result shows how much information, both quantum and classical can be transmitted between these nodes. We show that the amount of transferable information depends on the capacities of the inter connecting entangled resources. These results have a tremendous future application in the context of determining the optimal path in a quantum network to send the maximal possible information.

Abstract

In this work we specify various parameters like 1) local quantumness 2) entangling capability 3) classical randomness and give a canonical rep- representation of two qubit mixed quantum states based on them. Here we investigate the correlating capability of a non local Hamiltonian acting on general two qubit states in context of these parameters. In particular we address the questions like: 1.What is the rate of change of the standard measures of correlation like Entanglement (E) and Discord (D). 2.How these measures get affected by the change of the parameters. 3.For what choice of initial parameters, these rates of change of correlation like dE/dt ; dD/dt are maximum. 4.We study its application on bistable and open systems. Our study and analysis are completely based on the mixed quantum states quite unlike to the previous investigations based on pure quantum states.