Space Quantum Communication

A team of researchers based in China reported in Science on a milestone in quantum technologies research: the first quantum experiment initiated from a space satellite. Previous space experiments used existing satellites to mirror a signal sent from Earth back to Earth. This time the source of quantum correlation was on board of the satellite, which was launched in space with the specific purpose of performing this and future experiments.

A laser-setup sent correlated photons to two cities in China, 1200 km apart. Analysis of the joint probability counts measuring the polarisation correlations revealed the violation of Bell’s inequalities, a test to discriminate between quantum mechanics and other theories of reality (roughly speaking). Link

Besides testing the nature of physical reality, quantum correlations can be used to encrypt information, a feature investigated by the field of research known as quantum communication. An end application would be new protocols for cybersecurity.

While several countries and international collaborations are preparing to launch satellites for quantum experiments, China is certainly preeminent in the effort to establishing itself as the most advanced outpost for the implementation of quantum communication technology. Space is an integral part of that endeavour.

Chinese researchers plan to send to space other satellites to create a constellation within the next three years. Transmitting quantum information among different satellites allows to cover larger distances, as they occupy a part of space that is well over the lower (and thickest) part of the atmosphere, so that the signals can travel basically in vacuum, without suffering from absorption like on-ground open air transmission or optical fibre communication.

It is worth to point out that the very characteristic that make quantum information secure, forbids it to be amplified with the schemes employed in conventional communication. Also for space a bottleneck still remains: when light was beamed down to the ground stations, out of millions of photons per second, only a fraction could be detected. Enough to accomplish this result.

The team lead by J.W. Pan has then uploaded a report on another quantum effect, teleportation. As detailed in the pre-print, available on a publicly accessible Internet archive, this experiment involved instead sending single photons from a ground station to the satellite. Link

This is a collection of my articles on quantum technology, part of my Quantum Tech Newsletter. You can read the original posts also on Medium:

  1. Gravitational Quantum Sensors
  2. Quantum Advantage
  3. Analog Computing
  4. Quantum Internet
  5. Quantum Games
  6. Open-Source Quantum Tech
  7. Quantum Machine Learning
  8. Space Quantum Communication

© Nathan Shammah — 2018 and beyond.

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