This picture illustrates Micius satellite sending entangled photons to the two Chinese cities Delingha and Lijiang. (Jian-Wei Pan)


Something very exciting has happened recently in science. Entangled photons, produced in space have been beamed down to Earth and detected in two different Chinese cities, over 1200 km apart.  But what are these entangled particles in the first place? 

 The microscopic world, that one that is 10 000 000 000 times smaller than the thickness of the human hair is governed by completely different laws compared to the ones that describe the physics of our everyday life (Einstein.1905, Davisson and Germer.1927).  This subfield of physics called “Quantum Mechanics” can be very counterintuitive at times and the quantum entanglement is an epitome of its sophistications (Einstein et al. 1935, Schrödinger. 1935). It can happen that two or more systems in this microscopic world are produced in such a way that they cannot be described independently usually referred to as “spooky action at distance” (Einstein et al. 1935). Any time one of them experiences a certain interaction instantly the other one “feels” it. These systems can be as far from each other as you wish: the first in one edge of the universe and the other one in the other edge and this communication will always hold according to the laws of Quantum Mechanics. 

Photo illustrating the interaction of two entangled atoms at distance.

Such systems are said to be entangled (Einstein et al. 1935, Schrödinger. 1935).

Einstein and later Schrödinger, one of the pioneers of Quantum Mechanicsknew this was possible and physicists have succeeded to create entangled systems in their labs several times.

The latest experiment with entangled particles (photons) marks the first time an entangled system is produced in space and more precisely on the Chinese satellite called Micius (Yin et al. 2017). This is challenging because of vibrations and pressure fluctuations in space compared to the on-Earth conditions. But still this is not the only foremost achievement of this experiment. These two photons were also the first entangled quantum system to be detected 1200km apart and still remain entangled. Scientists (Yin et al. 2012) have tried before to conduct similar experiments but the particles could be detected entangled at the most 100km apart. Physicists check for the remaining level of entanglement after the photons arrive to the detector via the so-called Bell tests (Bell. 1964). The system of entangled particles has to resist the absorption from air, fiber optics or whatever the environment they are travelling through is. The advantage of this experiment is that the system was most of the time travelling without being disturbed by air or other particles, which was the initial reason why the photons were produced in a satellite.

Physicists aim to use quantum entanglement in world communication. Information transmitted with entangled systems is impossible to be disturbed by very fundamental laws of physics. If one tries to interfere in one of the signals it will immediately be transmitted to the initial signal too. This experiment might have already established a totally new period of safe communication.


COPYRIGHT: This article is property of We Speak Science, a nonprofit institution co-founded by Dr. Detina Zalli (Harvard University) and Dr. Argita Zalli (Imperial College London). The article is written by Bianka Mecaj (Master in High Energy Physics ETH, Zürich-Ecole Polytechnique )