A leap in quantum communication

A Dutch team from the University of Delft has found the missing link between Homo sapiens and Homo… quanticus, its hyperconnected successor. For the first time, researchers have made a link of a future communication network, 100% safe (in theory). It is called “quantum” in reference to the theory that describes the world of matter and whose mastered properties promise new applications in calculation, simulation or communication. Scientists have deployed the full range of quantum mechanical tools: qubit, entanglement, teleportation, memory, spin and colored diamonds… “It’s impressive such control”salutes Florian Kaiser, from the University of Stuttgart (Germany), reviewer of the article describing the prowess in Nature dated May 25.

The result is stunning. Let’s take Bob and Alice, canonical and fictional characters from the cryptography demonstrations. Now they can communicate, over a distance of 30 meters (in the laboratory), without any wires or fibers, and without anyone being able to intercept the signal, which is in fact literally teleported from one to the other.

How ? The researchers use the so-called quantum property of “entanglement”, highlighted in the 1980s, which makes it possible to manufacture a pair of grains of light, the two elements of which, called qubits, have irretrievably linked destinies: touching the one instantly modifies the other in a non-random fashion.

Multi-step entanglement

But how to “entangle” the two protagonists, Alice and Bob? A third thief, Charlie, is needed. On the principle that my friend’s friend is also my friend, Alice gets involved with Charlie, who gets involved with Bob. This done, Alice and Bob, by each possessing an element of an entangled pair, also become linked.

“Small” detail: for Charlie to bond with his two “friends” in this way, he must also have a quantum memory in order to wait for the processes of entanglement between him and Alice, then between him and Bob, to be carried out (the quantum friendship is not instantaneous and simple to make…). Another detail, the information is processed and stored in artificial diamonds; friendship is priceless.

The “teleporter” is ready. Bob, who by the way also needs a quantum memory, to give him time to prepare and send his message, sends the bits of information one by one, mixing them with the invisible channel that links him to Alice. The trick is played even if, in the case, Bob lost what he teleported to Alice, and each send must wait for a new entanglement to occur. “Teleportation consumes entanglement, which is its fuel, summarizes Ronald Hanson, project manager in Delft. For each qubit to be teleported, you must have entangled qubits twice. »

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A leap in quantum communication

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