Direct quantum communication without actual transmission of the message qubits

TL;DR

This paper proposes a secure quantum communication protocol that allows message transmission without transmitting the message-encoded qubits, utilizing entanglement swapping and the monogamy of entanglement for security.

Contribution

It introduces a new class of protocols enabling direct quantum communication without transmitting message qubits, expanding on previous orthogonal state methods under weaker conditions.

Findings

Protocol security relies on monogamy of entanglement.

Allows secure communication without transmitting message qubits.

Applicable to a large class of quantum states.

Abstract

Recently an orthogonal state based protocol of direct quantum communication without actual transmission of particles is proposed by Salih \emph{et al.}{[}Phys. Rev. Lett. \textbf{110} (2013) 170502{]} using chained quantum Zeno effect. As the no-transmission of particle claim is criticized by Vaidman {[}arXiv:1304.6689 (2013){]}, the condition (claim) of Salih \emph{et al.} is weaken here to the extent that transmission of particles is allowed, but transmission of the message qubits (the qubits on which the secret information is encoded) is not allowed. Remaining within this weaker condition it is shown that there exists a large class of quantum states, that can be used to implement an orthogonal state based protocol of secure direct quantum communication using entanglement swapping, where actual transmission of the message qubits is not required. The security of the protocol originates from monogamy of entanglement. As the protocol can be implemented without using conjugate coding its security is independent of non-commutativity.