Carrying an arbitrarily large amount of information using a single quantum particle
Li‐Yi Hsu, Ching–Yi Lai, You-Chia Chang, Chien-Ming Wu, Ray‐Kuang Lee · Physical Review A · 2020
Theoretically speaking, a photon can travel arbitrarily long before it enters into a detector, resulting in a click. How much information can a photon carry? We study a bipartite asymmetric ``two-way signaling'' protocol as an extension of that proposed by Del Santo and Daki\ifmmode \acute{c}\else \'{c}\fi{}. Suppose that Alice and Bob are distant from each other and each of them has an $n$-bit string. They are tasked to exchange the information of their local $n$-bit strings with each other, using only a single photon during the communication. It has been shown that the superposition of different spatial locations in a Mach-Zehnder (MZ) interferometer enables bipartite local encodings. We show that, after the travel of a photon through a cascade of $n$-level MZ interferometers in our protocol, the one of Alice and Bob whose detector clicks can access the other's full information of the $n$-bit string, while the other can gain one bit of information. That is, the wave-particle duality makes two-way signaling possible, and a single photon can carry an arbitrarily large (but finite) amount of information.