Researchers demonstrate quantum teleportation of patterns of light

September 21, 2017, Wits University
The core element of our quantum repeater is a cube of glass. We put two independent photons in, and as long as we can detect two photons coming out the other sides we know that we can perform entanglement swapping. Credit: Wits University

Nature Communications today published research by a team comprising Scottish and South African researchers, demonstrating entanglement swapping and teleportation of orbital angular momentum 'patterns' of light. This is a crucial step towards realizing a quantum repeater for high-dimensional entangled states.

Quantum communication over is integral to security and has been demonstrated in and fibre with two-dimensional states, recently over distances exceeding 1200 km between satellites. But using only two states reduces the information capacity of the photons, so the link is secure but slow. To make it secure and fast requires a higher-dimensional alphabet, for example, using patterns of light, of which there are an infinite number. One such pattern set is the (OAM) of light. Increased bit rates can be achieved by using OAM as the carrier of information. However, such photon states decay when transmitted over long distances, for example, due to mode coupling in fibre or turbulence in free space, thus requiring a way to amplify the signal. Unfortunately such "amplification" is not allowed in the quantum world, but it is possible to create an analogy, called a quantum repeater, akin to optical fibre repeaters in classical optical networks.

An integral part of a is the ability to entangle two photons that have never interacted - a process referred to as "entanglement swapping". This is accomplished by interfering two photons from independent entangled pairs, resulting in the remaining two photons becoming entangled. This allows the establishment of entanglement between two distant points without requiring one photon to travel the entire distance, thus reducing the effects of decay and loss. It also means that you don't have to have a line of sight between the two places.

Alphabet of OAM modes. OAM modes are sometimes called twisted light as the light appears as a ring with a vortex in the middle. The light can be twisted once, twice, three times and so on to create a high-dimensional alphabet. Credit: Wits University

An outcome of this is that the information of one can be transferred to the other, a process called teleportation. Like in the science fiction series, Star Trek, where people are "beamed" from one place to another, information is "teleported" from one place to another. If two photons are entangled and you change a value on one of them, then other one automatically changes too. This happens even though the two photons are never connected and, in fact, are in two completely different places.

In this latest work, the team performed the first experimental demonstration of entanglement swapping and teleportation for orbital angular momentum (OAM) states of light. They showed that quantum correlations could be established between previously independent photons, and that this could be used to send information across a virtual link. Importantly, the scheme is scalable to higher dimensions, paving the way for long-distance with high .

Schematic of the experiment. Four photons are created, one pair from each entanglement source (BBO). One from each pair (B and C) are brought together on a beam splitter. When all four photons are measured in together one finds that photons A and D, which previously where independent, are now entangled. Credit: Wits University


Present communication systems are very fast, but not fundamentally secure. To make them secure researchers use the laws of Nature for the encoding by exploiting the quirky properties of the quantum world. One such property is entanglement. When two particles are entangled they are connected in a spooky sense: a measurement on one immediately changes the state of the other no matter how far apart they are. Entanglement is one of the core resources needed to realise a quantum network.

Yet a secure communication link over long distance is very challenging: Quantum links using patterns of light languish at short distances precisely because there is no way to protect the link against noise without detecting the photons, yet once they are detected their usefulness is destroyed. To overcome this one can have a repeating station at intermediate distances - this allows one to share information across a much longer without the need for the information to physically flow over that link. The core ingredient is to get independent photons to become entangled. While this has been demonstrated previously with two-dimensional states, in this work the team showed the first demonstration with OAM and in high-dimensional spaces.

Explore further: Physicists use quantum memory to demonstrate quantum secure direct communication

Related Stories

Toward unbreakable encrypted messages

September 13, 2017

Chinese researchers recently announced a landmark advancement: They used a satellite orbiting Earth to beam pairs of quantum-entangled photons to two Tibetan mountaintops more than 700 miles apart. This distance blew the ...

Physicists add amplifier to quantum communication toolbox

June 1, 2017

Quantum encryption using single photons is a promising technique for boosting the security of communication systems and data networks, but there are challenges in applying the method over large distances due to transmission ...

Researchers take two big steps toward quantum computing

November 6, 2015

(—"Spooky action at a distance," Einstein's famous, dismissive characterization of quantum entanglement, has long been established as a physical phenomenon, and researchers are keen to develop practical applications ...

Recommended for you

Electrogates offer stop-and-go control in microfluidics

April 24, 2018

Although microfluidics devices have a wide variety of uses, from point-of-care diagnostics to environmental analysis, one major limitation is that they cannot be modified for different uses on the fly, since their flow paths ...

Strained materials make cooler superconductors

April 24, 2018

University of Wisconsin-Madison engineers have added a new dimension to our understanding of why straining a particular group of materials, called Ruddlesden-Popper oxides, tampers with their superconducting properties.


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (3) Sep 22, 2017
This article was not substantial. The Chinese already developed a quantum router so the answers put here was obvious. The experts saying "there is no way to protect the link against noise" did not think to use metamaterial to reduce noise and amplify signal or calculate for noise and then subtract the noise from the signal? I'm tired of reading very stupid articles that don't reach the furthest line of thinking, of investigations. It's becomes very tedious to believe and have confidence in Western science or for these "experts".
not rated yet Sep 24, 2017
The press release seems to imply the ability to transmit information faster than the speed of light. Supposedly, this is very unlikely to be true. What limits one's ability to transmit information over space-like separations in this set-up?
5 / 5 (1) Sep 24, 2017
If two photons are entangled and you change a value on one of them, then other one automatically changes too

Lies, lies, lies, this would require faster than C particle or energy transmission.

Change the value of one photon and the entanglement is broken, end of story.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.