We should be looking for traces of an interstellar quantum internet!

Of them astrophysicists from the University of Edinburgh, Arjun Berera and Jaime Calderón-Figueroa, recently published in the famous magazine Physical Review D an article that would undoubtedly have caught the attention of the founding members of the concepts behind the Seti program, for example Carl Sagan. The publication is freely available at arXiv and it delves into the question of whether a technologically advanced civilization could not use a technology from quantum information theory, namely the teleportation of a quantum state, to communicate with other members of The blue chain according to the title of the work of the former president of Seti-France, Albert Ducros.

The question arises all the more that if the quantum computing revolution leads to some of the dreams of its pioneers, a technologically advanced civilization could only use quantum computers precisely communicating with each other thanks to the EPR effect behind the concept of quantum teleportation. We suspect that we could pass a lot more information via quantum teleportation only with waves radio classics. On Earth, moreover, we seek to develop a kind ofInternet quantum using beams laser.

Quantum teleportation for dummies

Let’s do a few reminders about quantum teleportation by taking up what Futura had already explained on this subject.

It all started in 1993 when the physicist Charles Bennett and his colleagues (including Gilles Brassard and Claude Crépeau) working at IBM published an article in which they proposed a protocol experimental to allow the teleportation of quantum states. Four years later, the Austrian Anton Zeilinger published in Nature an article announcing that, along with other researchers, he had managed to implement Bennett’s ideas for quantum teleportation.

The performance and especially the name of the phenomenon of course immediately unleashed the enthusiasm of the fans of the series. star trek, seeing in it the hope of making real one of the greatest dreams of science fiction. Unfortunately, there is little chance of seeing one day with this quantum phenomenon the equivalents of Mr. Spock and Captain Kirk disappearing from the surface of pandora or a superearth to teleport back inside the Enterprise.

The reason is that in the experiments made by physicists, only a quantum state is teleported, therefore information, not matter. Furthermore, the system physical initial bearing information is destroyed. In the best case, a clone complete, memory and state of consciousness included, of one of the characters of star trek could eventually be rebuilt aboard the Enterprise, but the original would be well and truly dead.

Quantum teleportation itself relies on the phenomenon ofquantum entanglement theoretically discovered by Einstein and Schrödinger in the 1930s. It is this phenomenon that is at the heart of the famous ERP paradox and whose existence was verified in 1982 by Alain Aspect and his colleagues.

Capsule produced for the show What has become of the discoveries of yesteryear, broadcast on Canal Savoir. This excerpt traces the evolution of a discovery by Gilles Brassard (University of Montreal) and Claude Crépeau (McGill University), selected among the 10 discoveries of the year 1993 by Quebec Science : quantum teleportation. © Quebec Research Fund

When two particles are quantum entangled, certain physical quantities are determined for one of the two particles when they are measured on another. The effect seems instantaneous and if Alice on Earth makes a measurement on one of the particles entangled with that of Bob at thousands oflight yearsBob will have measurement results on his own particle which will depend on Alice’s, as if a signal had propagated from Alice to Bob much faster than light from the experiments carried out, but which do not prove that the effect is really instantaneous.

However, although correlations exist between the two particles that are transluminal, it is impossible to make a phone that would communicate faster than light this way.

We can still use a quantum state carrying a lot of information that would be transferred to Alice’s particle, by performing certain measurements, Alice would then teleport the quantum state and all the information to Bob’s particle.

But Bob could not extract the information encoded in his particle by subjecting it to certain measurements without knowing what the results of Alice’s own measurements were.

If Alice, for example, used a series of pairs of photons entangled laser to transmit a quantum state, it will for example have to send the results of its measurements to Bob by radio waves. Therefore, we cannot communicate faster than light between starsalthough it is suspected that the amount of transferable information would be much higher by working with quantum computers connected by quantum teleportation.

Now let’s do a few reminders about the Seti program and its history.

Seti on the trail of lasers

One of the motivations of Carl Saganwhen he helped develop the program Search for Extra-Terrestrial Intelligence, was to try to find out if we had a chance of surviving the XXe and XXIe centuries. Concretely Seti’s initial objective was to detect the signals of an extraterrestrial civilization with a radio telescope and if possible to determine if these signals contained a message to our destination… And to answer them.

The Cold War was in full swing in the last century and the proliferation of nuclear weapons did not bode well. Today the spectrum of atomic warfare has moved away. However, the consequences of global warming and the scarcity of natural resources, which accompany our overpopulated and irrational world, have not entirely exorcised it. The discovery of one or many ET civilizations could give us confidence in a future that seems very dark, if we are to believe the famous Meadows report predictions.

However, the best way to detect and make contact with a technologically advanced ET civilization may not be through the use of radio telescopes. The means would be in projects consisting of trying to detect emissions from ET civilizations in the form oflaser pulseswhether the by-product of propulsion techniques of solar sails interstellar, for example like those of the project Breakthrough Starshot, or real attempts at interstellar communications. The idea that extraterrestrials might prefer to communicate over interplanetary, and even interstellar distances, using lasers, is old. It has already been formulated by Schwartz and Townes in 1961, a year after Townes invented the laser, and two years after Cocconi and Morrison proposed the basic concept of the Seti program.

Some pictures of LaserSeti. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © Seti Institute

We are now almost ready to understand the work of Arjun Berera and Jaime Calderón-Figueroa.

We have already done quantum teleportation between the ground and a satellite in space, the Chinese have achieved remarkable performance in recent years on this subject.. Initially, they used a laser diode whose photons were entangled with a nonlinear optics device and sent into space to test ideas for a planetary quantum internet of the future.

One of the advantages of sending photons into space is that they quickly cross theatmosphere terrestrial to enter the vacuum of space. However, it turns out that, just as in the case of computers, the problem of decoherence must be solved with a quantum internet. Indeed, the quantum state carried by photons is fragile and it can be degraded by the environment they pass through, which limits the range of information transfer.

The two astrophysicists therefore asked themselves the question of how much entangled photons sent, say from the Earth in the direction of a exoplanet around Proxima Centauri, could faithfully teleport information. More generally, what would be the prospect for larger interstellar distances in the Milky Way.

They thus took into account theabsorption light by the gas and dust, disturbances from plasma particles and cosmic raysup to the influence of gravity stars, photons of the cosmic radiation or Sun.

Remarkably, there wouldn’t really be a problem and by operating with photons in the X-ray domain we could reach a distance of several million light-years, so downright a quantum internet that could be intergalactic.

Concretely, to demonstrate the existence of a transfer of information by quantum teleportation of ET origin, it would be necessary to find a double signal simultaneously, for example a laser beam in the visible like those which seek to detect the members of LaserSetiassociated with a radio signal which would provide the means to decipher the quantum state transferred by laser photons.

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