BEIJING (Reuters) — China has sent an “unbreakable” code from a satellite to the Earth, marking the first time space-to-ground quantum key distribution technology has been realized, state media said on Thursday.

China launched the world’s first quantum satellite last August, to help establish “hack proof” communications, a development the Pentagon has called a “notable advance”.

The official Xinhua news agency said the latest experiment was published in the journal Nature on Thursday, where reviewers called it a “milestone”.