Absolutely Secure Distributed Superdense Coding: Entanglement Requirement for Optimality

TL;DR

This paper demonstrates that optimal superdense coding requires maximal bipartite entanglement, introduces a secure protocol using GHZ states for arbitrary information, and extends it to distributed quantum communication scenarios.

Contribution

It establishes the necessity of maximal bipartite entanglement for optimality, introduces a secure superdense coding protocol with GHZ states, and develops a distributed scheme for secure quantum communication.

Findings

Maximal bipartite entanglement is necessary for optimal superdense coding.

GHZ states enable secure transmission of arbitrary information bits.

The protocol is applicable in distributed, multi-party quantum communication scenarios.

Abstract

Superdense coding uses entanglement as a resource to communicate classical information securely through quantum channels. A superdense coding method is optimal when its capacity reaches Holevo bound. We show that for optimality, maximal entanglement is a necessity across the bipartition of Alice and Bob, but neither absolute nor genuine multipartite entanglement is required. Unlike the previous schemes, which can transmit either even or odd bits of information, we have demonstrated a generalized dense coding protocol using the genuine multipartite entangled GHZ state to send arbitrary information bits. Expressed in the eigenbasis of different Pauli operators, GHZ state is characterized by a unique parity pattern which enables us to formulate a security checking technique to ensure absolute security of the protocol. We show this method to be equally applicable in a scenario, where the resource information is distributed among spatially separated parties. Finally, optimizing the number of qubit(s) sent to Bob, we construct a distributed dense coding method, which completely depicts absolutely secure one way quantum communication between many to one party.