Computers, smartphones, GPS: quantum physics has actually enabled numerous technological advances. It is now opening up brand-new fields of research in cryptography (the art of coding messages) with the aim of developing ultra-secure telecommunications networks. There is one obstacle, however: after a couple of hundred kilometers within a fiber optics, the photons that carry the qubits or quantum bits (the info) disappear. They for that reason require repeaters, a sort of relay, which are partly based upon a quantum memory. By handling to store a qubit in a crystal (a “memory”) for 20 milliseconds, a team from the University of Geneva (UNIGE) has actually set a world record and taken a major step towards the development of long-distance quantum telecoms networks. This research can be found in the journal npj Quantum Information.
Developed during the 20th century, quantum physics has actually allowed scientists to describe the behavior of particles and atoms along with specific residential or commercial properties of electromagnetic radiation. By braking with classical physics, these theories generated a real transformation and presented notions without equivalent in the macroscopic world such as superposition, which describes the possibility for a particle to be in numerous places simultaneously, or entanglement, which explains the capability of 2 particles to impact each other instantly even at a range ( spooky action at a range).
There is one barrier, however: after a couple of hundred kilometers within an optical fiber, the photons that bring the qubits or quantum bits (the information) disappear. By handling to save a qubit in a crystal (a “memory”) for 20 milliseconds, a team from the University of Geneva (UNIGE) has set a world record and taken a major action towards the advancement of long-distance quantum telecoms networks. Quantum theories make it possible to ensure perfect credibility and confidentiality for information (a qubit) when it is sent between two interlocutors by a particle of light (a photon) within an optical fiber. The phenomenon did not last long enough to permit the building and construction of a larger network of memories, a prerequisite for the advancement of long-distance quantum telecoms.
“This is a world record for a quantum memory based on a solid-state system, in this case a crystal.
Quantum theories are now at the heart of much research study in cryptography, a discipline that brings together strategies for encoding a message. Quantum theories make it possible to guarantee perfect credibility and privacy for details (a qubit) when it is transmitted between two interlocutors by a particle of light (a photon) within a fiber optics. The phenomenon of superposition let the sender know right away whether the photon conveying the message has been obstructed.
Remembering the signal
There is a significant barrier to the development of long-distance quantum telecommunication systems: beyond a couple of hundred kilometers, the photons are lost and the signal disappears. Since the signal can not be copied or amplified– it would lose the quantum state that ensures its privacy– the difficulty is to discover a way of duplicating it without altering it by creating repeaters based, in specific, on a quantum memory.
Crystal utilized for saving photonic qubits and lit up by a laser in a cryostat, an instrument for getting cryogenic temperature levels. Credit: (c) Antonio Ortu
In 2015, the team led by Mikael Afzelius, a senior lecturer in the Department of Applied Physics at the Faculty of Science of the University of Geneva (UNIGE), succeeded in saving a qubit carried by a photon for 0.5 milliseconds in a crystal (a memory). This process enabled the photon to move its quantum state to the atoms of the crystal prior to vanishing. Nevertheless, the phenomenon did not last long enough to enable the construction of a bigger network of memories, a prerequisite for the advancement of long-distance quantum telecoms.
Storage record
Today, within the framework of the European Quantum Flagship program, Mikael Afzelius team has managed to increase this period substantially by saving a qubit for 20 milliseconds. “This is a world record for a quantum memory based on a solid-state system, in this case a crystal.
” We applied a little electromagnetic field of one thousandth of a Tesla to the crystal and used dynamic decoupling approaches, which consist in sending extreme radio frequencies to the crystal. The impact of these strategies is to decouple the rare-earth ions from perturbations of the environment and increase the storage efficiency we have understood previously by almost an aspect of 40,” describes Antonio Ortu, a post-doctoral fellow in the Department of Applied Physics at UNIGE. The results of this research make up a major advance for the advancement of long-distance quantum telecommunications networks. They also bring the storage of a quantum state carried by a photon to a time scale that can be approximated by people.
An effective system in ten years
“The obstacle now is to extend the storage time even more. In theory, it would be enough to increase the duration of exposure of the crystal to radio frequencies, however for the time being, technical challenges to their application over a longer period of time avoid us from going beyond 100 milliseconds.
The researchers will also need to discover ways of creating memories efficient in keeping more than a single photon at a time, and thus of having knotted photons which will ensure privacy. “The objective is to establish a system that carries out well on all these points which can be marketed within 10 years,” concludes the scientist.
Referemce: “Storage of photonic time-bin qubits for up to 20 ms in a rare-earth drugged crystal” by Antonio Ortu, Adrian Holzäpfel, Jean Etesse and Mikael Afzelius, 15 March 2022, npj Quantum Information.DOI: 10.1038/ s41534-022-00541-3.