Developing long-distance quantum telecommunications networks —


Computer systems, smartphones, GPS: quantum physics has enabled many technological advances. It’s now opening up new fields of analysis in cryptography (the artwork of coding messages) with the goal of growing ultra-secure telecommunications networks. There’s one impediment, nevertheless: after a number of hundred kilometers inside an optical fiber, the photons that carry the qubits or ‘quantum bits’ (the knowledge) disappear. They subsequently want ‘repeaters’, a sort of ‘relay’, that are partly primarily based on a quantum reminiscence. By managing to retailer a qubit in a crystal (a “reminiscence”) for 20 milliseconds, a staff from the College of Geneva (UNIGE) has set a world file and brought a serious step in direction of the event of long-distance quantum telecommunications networks. This analysis could be discovered within the journal npj Quantum Data.

Developed in the course of the twentieth century, quantum physics has enabled scientists to explain the conduct of atoms and particles in addition to sure properties of electromagnetic radiation. By breaking with classical physics, these theories generated an actual revolution and launched notions with out equal within the macroscopic world equivalent to superposition, which describes the chance for a particle to be in a number of locations without delay, or entanglement, which describes the flexibility of two particles to have an effect on one another instantaneously even at a distance (‘spooky motion at a distance’).

Quantum theories are actually on the coronary heart of a lot analysis in cryptography, a self-discipline that brings collectively strategies for encoding a message. Quantum theories make it potential to ensure excellent authenticity and confidentiality for data (a qubit) when it’s transmitted between two interlocutors by a particle of sunshine (a photon) inside an optical fiber. The phenomenon of superposition let the sender know instantly whether or not the photon conveying the message has been intercepted.

Memorizing the sign

Nevertheless, there’s a main impediment to the event of long-distance quantum telecommunication techniques: past a number of hundred kilometers, the photons are misplaced and the sign disappears. Because the sign can’t be copied or amplified — it might lose the quantum state that ensures its confidentiality — the problem is to discover a manner of repeating it with out altering it by creating ‘repeaters’ primarily based, particularly, on a quantum reminiscence.

In 2015, the staff led by Mikael Afzelius, a senior lecturer within the Division of Utilized Physics on the College of Science of the College of Geneva (UNIGE), succeeded in storing a qubit carried by a photon for 0.5 milliseconds in a crystal (a ‘reminiscence’). This course of allowed the photon to switch its quantum state to the atoms of the crystal earlier than disappearing. Nevertheless, the phenomenon didn’t final lengthy sufficient to permit the development of a bigger community of recollections, a prerequisite for the event of long-distance quantum telecommunications.

Storage file

Right this moment, inside the framework of the European Quantum Flagship program, Mikael Afzelius’ staff has managed to extend this length considerably by storing a qubit for 20 milliseconds. “It is a world file for a quantum reminiscence primarily based on a solid-state system, on this case a crystal. We have now even managed to succeed in the 100 millisecond mark with a small lack of constancy,” enthuses the researcher. As of their earlier work, the UNIGE scientists used crystals doped with sure metals known as ‘uncommon earths’ (europium on this case), able to absorbing gentle after which re-emitting it. These crystals had been saved at -273,15°C (absolute zero), as a result of past 10°C above this temperature, the thermal agitation of the crystal destroys the entanglement of the atoms.

“We utilized a small magnetic subject of 1 thousandth of a Tesla to the crystal and used dynamic decoupling strategies, which consist in sending intense radio frequencies to the crystal. The impact of those strategies is to decouple the rare-earth ions from perturbations of the atmosphere and improve the storage efficiency we’ve identified till now by virtually an element of 40,” explains Antonio Ortu, a post-doctoral fellow within the Division of Utilized Physics at UNIGE. The outcomes of this analysis represent a serious advance for the event of long-distance quantum telecommunications networks. In addition they deliver the storage of a quantum state carried by a photon to a time scale that may be estimated by people.

An environment friendly system in ten years

Nevertheless, there are nonetheless a number of challenges to be met. “The problem now’s to increase the storage time additional. In principle, it might be sufficient to extend the length of publicity of the crystal to radio frequencies, however in the intervening time, technical obstacles to their implementation over an extended time frame stop us from going past 100 milliseconds. Nevertheless, it’s sure that these technical difficulties could be resolved,” says Mikael Afzelius.

The scientists may even have to seek out methods of designing recollections able to storing greater than a single photon at a time, and thus of getting ‘entangled’ photons which is able to assure confidentiality. “The goal is to develop a system that performs properly on all these factors and that may be marketed inside ten years,” concludes the researcher.

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