  The development of modern technology extends human presence beyond cislunar
space and onto other planets, which presents an urgent need for high-capacity,
long-distance and interplanetary communication. Communication using photons as
carriers has a high channel capacity, but the optical diffraction limit in deep
space leads to inevitable huge geometric loss, setting an insurmountable
transmission distance for existing optical communication technologies. Here, we
propose and experimentally demonstrate a photon-inter-correlation optical
communication (PICOC) against an ultra-high channel loss. We treat light as a
stream of photons, and retrieve the additional information of internal
correlation and photon statistics globally from extremely weak pulse sequences.
We successfully manage to build high-fidelity communication channel with a loss
up to 160dB by separating a single-photon signal embedded in a noise ten times
higher. With only commercially available telescopes, PICOC allows establishment
of communication links from Mars to Earth communication using a milliwatt
laser, and from the edge of the solar system to Earth using a few watts laser.
