Authenticated bidirectional quantum secure direct communication with single photons

Abstract In this paper, a novel authenticated bidirectional quantum secure direct communication (ABQSDC) scheme is constructed by using single photons in both polarization and spatial-mode degrees of freedom, which is able to simultaneously exchange the private bit sequences between two remote users while authenticating their identifications. This scheme is verified to have no information leakage problem and be immune to the outside active attacks. This scheme only needs single photons in two degrees of freedom as quantum resource and single-photon measurements, and has a qubit efficiency of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:math> . This scheme has a quantum communication capacity of four classical bits carried by one single photon in two degrees of freedom, and does not need to generate the initial quantum resource specially. This scheme has good practical feasibility with current quantum technologies.