Dense coding using entangled input states

O. Akhavan, A.T. Rezakhani, M. Golshani

Zhang Guo

According to the theory that quantum entanglement can be used in quantum dense coding and increase the classical information capacity of a quantum channel, we discuss and compare the upper bound of capacity for dense coding in two case of using entangled input states and using product input states though a noiseless channel, when using a pure entanglement resource and get the result,i. e. , the capacity of dense coding using entangled input states is no larger than the capacity for product input states.

Liang Qiu, An Min Wang, XIAO SAN MA

Jiahua Wei, Lei Shi, Shanghong Zhao +5 more

Z. Shadman, Hermann Kampermann, Chiara Macchiavello +1 more

We investigate super dense coding in the presence of noise, i.e. the subsystems of the entangled resource state have to pass a noisy unital quantum channel between the sender and the receiver. We discuss explicitly the case of Pauli channels in an arbitrary dimension and derive the super dense coding capacity (i.e. the optimal information transfer) for some given resource states. For the qubit depolarizing channel, we also optimize the super dense coding capacity with respect to the input state. We show that, below a threshold value of the noise parameter, the super dense coding protocol is optimized by a maximally entangled initial state, while above the threshold it is optimized by a product state. Finally, we provide an example of a noisy channel where non-unitary pre-processing increases the super dense coding capacity, as compared to only unitary encoding.

Pavel Lougovski, Dmitry B. Uskov

Entanglement can effectively increase communication channel capacity as evidenced by dense coding that predicts a capacity gain of 1 bit when compared to entanglement-free protocols. However, dense coding relies on Bell states and when implemented using photons the capacity gain is bounded by $0.585$ bits due to one's inability to discriminate between the four optically encoded Bell states. In this paper we study the following question: Are there alternative entanglement-assisted protocols that rely only on linear optics, coincidence photon counting and separable single photon input states and at the same time provide a greater capacity gain than $0.585$ bits. We show that besides the Bell states there is a class of bipartite four-mode two-photon entangled states that facilitate an increase in channel capacity. We also discuss how the proposed scheme can be generalized to the case of two-photon $N$-mode entangled states for $N=6,8$.