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via:CnBeta time:2019/9/20 13:31:00 readed:765

The scene of satellite-ground experiments carried out by Ali Earth Station and Mozi satellite. The green light is the beacon light emitted by the satellite, and the red is the beacon light emitted by the ground.

Quantum mechanics and gravity theory are the two pillars of modern physics. They have achieved great success in their respective fields. But any theoretical work that tries to integrate them has encountered great difficulties.

Among the four basic interactions known at present, electromagnetic, weak interaction and strong interaction have been quantized and unified. Only the quantification of gravitational interaction has been unresolved, and the solution, or a correct understanding of this problem, will contribute to the establishment of a unified theory of the four basic interactions. This is one of the most important issues concerned by many scientists in physics, including Einstein.

In the experiment scenario, in order to improve the intensity of the signal light, three devices were used to work together. Two telescopes in the picture simultaneously emitted beacons to the satellite.

At present, there are many models on how to integrate quantum mechanics and gravity theory, but they are lack of experimental test and can not be verified, which seriously hinders the development of science. One of the main reasons is that the predictions of these theoretical models can only be tested under extreme experimental conditions, such as the minimal spatial scale.

10 m 35 m, specific electron radius

The 10-15 metres are 20 orders of magnitude smaller, or extremely high energy scales.

1016 TeV (trillion electron volts), and the current large hadron colliders such as the LHC can only increase proton energy to 10 TeV, which is far beyond the experimental conditions currently available.

General relativity foretells a kind of strange space-time structure that violates the law of causality-going back to the past, like the "time machine" in science fiction. In the theory of quantum gravity, this kind of space-time structure is particularly important, because in principle it can be formed by the spatial-temporal geometric fluctuations of quantum gravity.

However, the destruction of causality by time machine will lead to many logical paradoxes. In order to avoid this problem, Polchinski, a famous American physicist, first put forward a theoretical solution. He pointed out that there is a special and self-consistent evolution process of classical objects in this kind of space-time structure, and there is no logical paradox. American physicist Politzer and British physicist Deutsch et al extended the theory and studied the self-consistent evolution behavior of quantum states in this kind of space-time structure.

Ali earth station binoculars for quantum communication with Mozi

On this basis, the Australian physicist Ralph et al. further proposed a theory called "event formalism". The theory holds that the evolution of quantum states in singular space-time is different from that in straight space-time. Gravitation may lead to the decoherence of entangled quantum states, and predicts the decoherence between earth stars. The distributed entangled photon pairs will be decoherent.

Suppose a pair of entangled photonic pairs are prepared on the earth's surface, one of which propagates through the local flat space-time and propagates near the surface of the light source, while the other propagates to the satellite through the curved space-time formed by the Earth's gravitational field. According to the existing quantum mechanics theory, all entangled photonic pairs will maintain entanglement, while according to the "event form" theory, the correlation between entangled photonic pairs will be probabilistic lost.

The satellite-to-ground docking scene between the experimenter and the Ali ground station and Mozi

The experimental satellite of quantum science is the ideal platform to test this theory. Pan Jianwei's team has carried out a series of innovative experiments on the distribution of quantum states between Earth stars. On August 16, 2016, China launched the world's first quantum science experiment satellite, Mozi. By August 2017, Mozi had successfully accomplished three established scientific goals: 1,000-kilometer-scale bi-directional quantum entanglement distribution, quantum key distribution and quantum teleportation.

Thanks to the previous experimental work and technical accumulation of Mozi quantum science experimental satellite, this study is the first in the world to carry out the experimental test of gravitational induced quantum entanglement decoherence in space, and to test the decoherence of quantum entangled photons passing through the gravitational field of the earth. Finally, through a series of exquisite experimental design and theoretical analysis, this experiment is convincing to eliminate the phenomenon of entanglement decoherence caused by gravity predicted by the previous "event form" theory, and on the basis of the experimental results, the previous theoretical model is modified and improved. The modified theory shows that the entanglement decoherence phenomenon will be weak at the altitude of 500 km orbit of Mozi. In order to further verify the certainty, it is necessary to carry out research on the experimental platform of higher orbit in the future.

An Ali ground station binoculars under delay photography for quantum communication with Mozi.

This is the first experimental study on the relationship between quantum mechanics and gravity theory carried out by satellite in space. It is of guiding significance and will greatly promote relevant theoretical and experimental research activities.

One of the beauty of scientific research is that it is unexpected.

"We can use standard quantum mechanics to predict this scenario, but we are open to possible experimental results. Any 'unexpected' results will herald that our understanding of existing quantum mechanics and gravity theory needs to be significantly revised. " Although there is no "surprise" in this experiment within the range of experimental accuracy, we rule out a class of quantum decoherence models caused by gravity, Pan Jianwei said. This is a positive development for the study of the relationship between quantum mechanics and gravity theory.

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