Researchers change wavelengths of entangled photons to those used in telecommunications

September 26, 2017
Schematic of the emission of entangled photon pairs from a quantum dot. Credit: Sascha Kolatschek

The potential for photon entanglement in quantum computing and communications has been known for decades. One of the issues impeding its immediate application is the fact that many photon entanglement platforms do not operate within the range used by most forms of telecommunication.

An international team of researchers has started to unravel the mysteries of , demonstrating a new nanoscale technique that uses semiconductor to bend photons to the wavelengths used by today's popular C-band standards. They report their work this week in Applied Physics Letters.

"We have demonstrated the emission of polarization-entangled photons from a quantum dot at 1550 nanometers for the first time ever," said Simone Luca Portalupi, one of the work's authors and a senior scientist at the Institute of Semiconductor Optics and Functional Interfaces at the University of Stuttgart. "We are now on the wavelength that can actually carry quantum communication over long distances with existing telecommunication technology."

The researchers used quantum dots created from an indium arsenide and gallium arsenide platform, producing pure single photons and entangled photons. Unlike parametric down-conversion techniques, quantum dots allow for photons to be emitted only one at a time and on demand, crucial properties for . A distributed Bragg reflector, which is made from multiple layered materials and reflects over a wide spectrum, then directed the photons to a microscope objective, allowing them to be collected and measured.

Researchers and industry leaders have found that the C-band—a specific range of infrared wavelengths—has become an electromagnetic sweet spot in telecommunications. Photons traveling through both optical fibers and the atmosphere within this range experience significantly less absorption, making them perfect for relaying signals across .

"The telecom C-band window has the absolute minimum absorption we can achieve for signal transmission," said Fabian Olbrich, another of the paper's authors. "As scientists have made discoveries, industry has improved technology, which has let scientists make more discoveries, and so now we have a standard that works very well and has low dispersion."

Most entangled photons originating from quantum dots, however, operate near 900 nanometers, closer to wavelengths we can see with the naked eye.

The researchers were impressed by the quality of the signal, Olbrich said. Other efforts to shift the emission wavelength of polarization-entangled photons of quantum dots toward the C-band tended to increase the exciton fine-structure splitting (FSS), a quantity that should be close to zero for entanglement generation. Olbrich's team reports their experiment experienced less than one-fifth as much FSS as other studies in the literature.

"The chance to find a quantum dot that is able to emit polarization-entangled photons with high fidelity is quite high for our specific study," Olbrich said.

With each successful experiment, the quantum communications community is seeing its field bend toward greater applicability in today's telecommunications industry. Researchers hope that one day, entangled photons will impact cryptography and secure satellite communications.

"The hard part now is to combine all the advantages of the system and fulfill prerequisites such as high photon indistinguishability, high temperature operation, increased flux and out coupling efficiency that would make them work," Olbrich said.

Explore further: Toward unbreakable encrypted messages

More information: "Polarization-entangled photons from an InGaAs-based quantum dot emitting in the telecom C-band," Applied Physics Letters (2017). DOI: 10.1063/1.4994145

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 ...

Quantum electronics: Two photons and chips

January 20, 2006

Scientists at Toshiba Research Europe Limited (Cambridge, UK) believe they are on to a way of producing entangled twins of photons using a simple semiconductor electronic device. Such a chip-based source of entangled photons ...

Researchers develop ideal single-photon source

September 7, 2015

With the help of a semiconductor quantum dot, physicists at the University of Basel have developed a new type of light source that emits single photons. For the first time, the researchers have managed to create a stream ...

New technique for creation of entangled photon states

February 15, 2017

Members of the Faculty of Physics at the Lomonosov Moscow State University have elaborated a new technique for creating entangled photon states. They have described their research in an article published in the journal Physical ...

Recommended for you

How the Earth stops high-energy neutrinos in their tracks

November 22, 2017

Neutrinos are abundant subatomic particles that are famous for passing through anything and everything, only very rarely interacting with matter. About 100 trillion neutrinos pass through your body every second. Now, scientists ...

Quantum internet goes hybrid

November 22, 2017

In a recent study published in Nature, ICFO researchers led by ICREA Prof. Hugues de Riedmatten report an elementary "hybrid" quantum network link and demonstrate photonic quantum communication between two distinct quantum ...

Enhancing the quantum sensing capabilities of diamond

November 22, 2017

Researchers have discovered that dense ensembles of quantum spins can be created in diamond with high resolution using an electron microscopes, paving the way for enhanced sensors and resources for quantum technologies.

0 comments

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.