SECURE INFORMATION EXCHANGE WITHOUT PRIOR KEY DISTRIBUTION VIA SINGLE-PHOTON HYPERSTATES

Methods for two distant parties to exchange their secret messages usingsingle photons are considered. There existed several such methods but theyare either insecure or face with information leakage\ problem. Recently, Ye \textit{et al.} [Quantum Inf. Process. 20 (2021) 209] have reported a methodusing single photons in both polarization and spatial degrees of freedomthat is both efficient and resistant from information leakage. However, thismethod is not so feasible as it has specific limitations, namely, itrequires availability of quantum memory and high classical communicationcost. We propose in this paper a new method to overcome the above-saidlimitations. Our method is also efficient because we also use single photonsin two degrees of freedom. However, the encoding operation in our method ismodified so that no quantum memory is demanded at all and the execution ofour method is simpler compared to the method of Ye \textit{et al.}.Moreover, the cost of classical communication in our method is 50\% cheaperthan that in the method of Ye \textit{et al.} Therefore, our method provesto be feasible, simple and economical that could be realized by means ofcurrent technologies.