Nav: Home

A network of crystals for long-distance quantum communication

May 29, 2017

Quantum physic can guarantee that a message has not be intercepted before reaching its destination. Thanks to the laws of quantum physic, a particle of light - a photon - can be in two distinct states simultaneously, comparable to a coin thrown in the air, which is virtually both head and tail before reaching the ground. Like when the coin is grabbed, this superposition of states is destroyed as soon as it is read. This peculiar feature allow one to detect an evil eavesdropper when sending a message. However, this technique is so far limited to short distances. In order to extend the reach of these quantum communications, researchers from the University of Geneva (UNIGE), Switzerland, have demonstrated a novel protocol based on a crystal than can emit quantum light as well as store it for arbitrary long times. This work, to appear in Physical Review Letters, paves the way for a future quantum repeater.

Quantum superposition is one of the fascinating features of quantum physic. "In order to test the security of communication link, we can use particles of light, photons, onto which we encode quantum bits (analogous to the bit used in computing) ", explains Cyril Laplane, a researcher in the Group of Applied Physics at UNIGE. He continues: "We then take advantage of the properties of quantum superposition, allowing the photon to be simultaneously in two states, to test the security of a communication link". Indeed if the photon is intercepted and read, the superposition of states is lost, only one of the two states remains. Hence, the recipient can know if the message has been intercepted.

The need for quantum repeaters

Since this protocol relies on the use of single photons, there is an unneglectable chance of losing the particles when they propagate in traditional communication links such as the optical fiber. This problem becomes more and more critical with the distance. In order to communicate over long distances, one would need repeaters, which amplify and rebroadcast the signal. It is however impossible to use such procedure in quantum communication without destroying the superposition of states. Physicists need to build a quantum repeater able to store the dual character of the photon but also produce such state, a true challenge.

A crystal based solution

To build a quantum repeater, scientists have investigated a lot atomic gases, which usually require heavy experimental apparatus. "We are using a crystal capable of storing quantum state of light. It possesses the advantage of being relatively simple to use with potential for very long storage times", clarifies Jean Etesse, a co-author of the paper. These crystals are able to absorb light and restore it later, without reading the information encoded on it. Furthermore, they can generate single photons and store them on demand. Another major asset is their potential for miniaturisation.

Since the crystal is the source and memory for quantum information, it simplifies the protocol for quantum repeaters and lays the foundation of a quantum internet. Physicists at UNIGE are already working on the creation of an elementary link of quantum communication using a repeater.
-end-


Université de Genève

Related Photons Articles:

Photons and electrons one on one
The dynamics of electrons changes ever so slightly on each interaction with a photon.
An advance in molecular moviemaking shows how molecules respond to two photons of light
Some of the molecules' responses were surprising and others had been seen before with other techniques, but never in such detail or so directly, without relying on advance knowledge of what they should look like.
The imitation game: Scientists describe and emulate new quantum state of entangled photons
A research team from ITMO University, MIPT and Politecnico di Torino, has predicted a novel type of topological quantum state of two photons.
What if we could teach photons to behave like electrons?
The researchers tricked photons - which are intrinsically non-magnetic - into behaving like charged electrons.
Producing single photons from a stream of single electrons
Researchers at the University of Cambridge have developed a novel technique for generating single photons, by moving single electrons in a specially designed light-emitting diode (LED).
Counting photons is now routine enough to need standards
NIST has taken a step toward enabling universal standards for single-photon detectors (SPDs), which are becoming increasingly important in science and industry.
Scientists have found out why photons flying from other galaxies do not reach the Earth
In the Universe there are extragalactic objects such as blazars, which very intensively generate a powerful gamma-ray flux, part of photons from this stream reaches the Earth, as they say, directly, and part -- are converted along the way into electrons, then again converted into photons and only then get to us.
Researchers discover new way to split and sum photons with silicon
A team of researchers at The University of Texas at Austin and the University of California, Riverside have found a way to produce a long-hypothesized phenomenon -- the transfer of energy between silicon and organic, carbon-based molecules -- in a breakthrough that has implications for information storage in quantum computing, solar energy conversion and medical imaging.
Breaking the limits: Discovery of the highest-energy photons from a gamma-ray burst
Gamma-ray bursts (GRBs) are brief and extremely powerful cosmic explosions, suddenly appearing in the sky, about once per day.
Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.
More Photons News and Photons Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.