A brief introduction to the contributions of Mo Zi to optics will be presented, followed by an account of the development of quantum optics in China over the past two decades, up to the launch of the Mo Zi satellite. I will also attempt to clear up some of the common misconceptions and misrepresentations in the media about quantum communications.
Unknown in the west, and even to many Chinese, the earliest written records of optics appeared in China. The Mo Jing (Book of Mo Zi) written by Mo Zi, who was born in ~470 BCE and predates Euclid by a hundred years, is the earliest extant treatise on logic, geometry, optics and mechanics in China. The section on optics is clearly based on actual experiments, with an account of the basic concepts of linear optics, including reflection by plane and curved mirrors, the pinhole camera, and refraction. Later, Liu An (179-122 BCE) also compiled several works where novel optical devices are mentioned, such as burning glasses made of ice, and the earliest surveillance periscope. However, this was followed by a long period during which scientific thought stagnated, and it was only after glass lenses were introduced from the west that optics was revived as a field of study. Henceforth, China followed the footsteps of foreign scientists. It is only in recent years that we have begun to catch up with the west. The Quantum Science Satellite (QUESS, also nicknamed the Mo Zi satellite), launched on 17 August 2016, is representative of the progress we have achieved in quantum optics and engineering, based on over twenty years of hard work. The mission of the satellite is to perform experiments on quantum key distribution and tests of Bell’s inequality from space to the Earth. If successful, this will be followed by the creation of actual quantum key distribution channels between various locations within and outside China.