On January 18th, 2017, Mozi, the world's first quantum communication satellite, has been handed over to scientists for the official start of scientific experiments after its 4-month in-orbit test came to a successful end. The ceremony was held in Beijing and the satellite will soon been put into service for testing the phenomena of quantum entanglement and 'unhackable' quantum communication.
Picture 1. Xinglong station interacting with QUESS during testing (By National Astronomical Observatories/CAS)
Mozi, or Micius, after the famous 5th century BCE Chinese scientist, is developed independently by China, and launched into Earth orbit around 500 km above ground on August 16th, 2016, winning applauses from media worldwide. The main instrument of the 600 kg craft is a "Sagnac" interferometer that is used to generate two entangled infrared photons by shining an ultraviolet laser on a non-linear optical crystal.
Picture 2. Mozi (By Popular Science)
The project into a brand new field of space-scale quantum experiment is led by Outstanding Frontier Innovation Center for Quantum Information and Quantum Science and Technology, CAS, which locates in USTC. It is a collaborative endeavor between USTC, SITP(Shanghai Institute of Technical Physics of The Chinese Academy of Sciences), SECM(Shanghai Engineering Center for Microsatellites) , IOE(Institute of Optics and Electronics, Chinese Academy of Sciences), NAOC(National Astronomical Observatories, Chinese Academy of Sciences), and NSSC(National Space Science Center, CAS). Starting from 2003, it took researchers over 10 years from QUESS(The Quantum Experiments at Space Scale) first put forward to the theories and techniques needed fully developed.
Two Missions: Quantum Communication and Quantum Entanglement
Cryptography operates through the use of an encryption key (such as a numbers pad), which, when applied to an encryption algorithm, can be used to decrypt or encrypt a message. Quantum entanglement is the act of fusing two or more particles into complementary “quantum states.” In such states, no particle can be independently described. Instead the particles exist in a hazy shared quantum state that “collapses” when observed. A quantum key is a string of ones and zeros, representing the quantum states of particles, thus any would-be eavesdroppers will lead to collapse, making it secure in nature to encode and decode messages.
Figure 1. Quantum communication (By Artur Ekert)
Mozi is mainly applied to demonstrate quantum key distribution (QKD) between the satellite and two stations on the ground – the Nanshan telescope at the Xinjiang Astronomical Observatory and the Xinglong Observatory in Yanshan. If succeeds, Mozi will be able to transfer quantum keys at 10k bps from space to the ground, 1015 times faster than optical fiber quantum communication. It provides not only quantum communication, with high security level, but also reliable technical support for a global quantum communication network in the future.
Another aim for Mozi is an unprecedented scientific experiment to see if quantum entanglement can operate over long distances by sending entangled photons from the satellite to ground stations. This "spooky action at a distance" described by Albert Einstein will be established at a speed of 1 pair per sec in China and Austria, which are separated by around 1,200 kilometers. It’ll also quantum teleport a photon state from the Ali observatory on the Tibetan Plateau to the satellite. Further tests into general relativity, quantum gravity are expected to push forward basic physics.
Figure 2. Quantum teleportation (By Nature News)
A New Era for Chinese Space Science and Quantum Communication
The 4-month in-orbit test proved satisfactory in multiple requirements for space quantum scientific experiments, especially for a high-frequency and high-accuracy satellite tracking system. Now that Mozi has returned with success, it came to use at last.
"All our teams will continue their efforts to finish three experimental missions as early as possible in the next few months by making good use of the currently favorable conditions." said mission designer and chief scientist Jianwei Pan, an academic at the Chinese Academy of Sciences, also a respected professor of USTC.
Picture 3. Part of the testing team with Mozi passing by (By CAS)
As a significant step towards a future worldwide quantum internet, Mozi marked a new era of Chinese space science and quantum communication. Through their talents and diligent work, we believe all the researchers behind it have impressed and will go on to impress the world with Chinese power.