Economic No-Key Semi-Quantum Direct Communication Protocol

While secure communication between two quantum parties has been shown possible theoretically, what is the possible direct communication between a full quantum capability sender Alice and a limited quantum capability receiver Bob? This is called Semi- Quantum Direct Communication (SQDC). Several protocols have been proposed for secure SQDC. However, they all need a pre-shared key and at least linear entanglement preservation time, as well as a linear number of quantum bit registers, with respect to message length. Besides, complex hardware implementation (including quantum bit permutations) decreases the transmission efciency. This paper introduces a no-key SQDC protocol requiring only constant entanglement preservation time and a xed number of quantum bit registers by adding an authentic public classical channel. The quantum circuit complexity of Alice decreases considerably as well as the number of quantum bits transmitted for sending a xed length message. Moreover, the protocol is provably secure if some precondition is satised