Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New approach uses 'twisted light' to increase efficiency of quantum cryptography systems

23.03.2015

Researchers demonstrate how to encode 2.05 bits per photon, doubling existing systems that use light polarization

Researchers at the University of Rochester and their collaborators have developed a way to transfer 2.05 bits per photon by using "twisted light." This remarkable achievement is possible because the researchers used the orbital angular momentum of the photons to encode information, rather than the more commonly used polarization of light. The new approach doubles the 1 bit per photon that is possible with current systems that rely on light polarization and could help increase the efficiency of quantum cryptography systems.

Quantum cryptography promises more secure communications. The first step in such systems is quantum key distribution (QKD), to ensure that both the sender and receiver - usually referred to as Alice and Bob - are communicating in such a way that only they know what is being sent. They are the only ones who hold the "key" to the messages, and the systems are set up in such a way that the presence of any eavesdropper would be identified.

In the paper, published in New Journal of Physics today, Mohammad Mirhosseini and his colleagues describe a proof-of-principle experiment that shows that using OAM to encode information rather than polarization opens up the possibility of high-dimensional QKD. Mirhosseini, a Ph.D. student in Robert W. Boyd's group at the University of Rochester's Institute of Optics, explains that they were able to encode a seven dimensional "alphabet" - that is, seven letters or symbols - using both the orbital angular momentum (OAM) of the photons and their angular position (ANG). These two properties of the photons form what physicists refer to as mutually unbiased bases, a requirement for QKD. Using mutually unbiased bases, the correct answer is revealed only if Alice encodes the information using a particular basis and Bob measures in that same basis.

In QKD, once they have generated a long, shared key, Alice and Bob publicly announce the basis (or "alphabet") they have used for each symbol in the key. They then compare what alphabet was used for sending and which one for receiving. They only keep the part of the key in which they have used the same "alphabet." The letters they keep produce a secure key, which they can use to encrypt messages and transmit these with regular encryption without the need for quantum cryptography.

If for any reason their communication is intercepted, because of a fundamental property of quantum mechanics, there will be discrepancies between Alice and Bob's keys. To check for this, Alice and Bob sacrifice a short part of their key. They share this publicly and identify any discrepancies. This lets them know whether their connection is secure and, if not, they will stop the communication.

The researchers showed that using their system they were able to generate and detect information at a rate of 4kHz and with 93% accuracy. A long term goal of the research is to realize secure communications at GHz transmission rates, which is desirable for telecommunication applications.

"Our experiment shows that it is possible to use "twisted light" for QKD and that it doubles the capacity compared to using polarization," said Mirhosseini. "Unlike with polarization, where it is impossible to encode more than one bit per photon, "twisted light" could make it possible to encode several bits, and every extra bit of information encoded in a photon means fewer photons to generate and measure."

In a previous experiment using a strong laser beam instead of single photons, Boyd's team were able to measure up to 25 modes of OAM and ANG. This is equivalent to having 25 letters available in your "alphabet" rather than 7. This shows the potential for a system like the one described in the new paper to have the capacity to transmit and measure 4.17 bits per photon using more sophisticated equipment.

Mirhosseini acknowledges that the real-world challenges are not straightforward to overcome but when it comes to QKD, he is excited about the possibilities their system opens up.

###

Mirhosseini's collaborators included his colleagues O. S. Magana-Loaiza, M. N. O'Sullivan, B. Rodenburg, M. Malik (now at the IQOQI in Vienna), and advisor Robert W. Boyd (who also holds the Canada Excellence Research Chair in Quantum Nonlinear Optics at the University of Ottawa) at the University of Rochester; M. P. J. Lavery and M. J. Padgett from the University of Glasgow; and D. J. Gauthier from Duke University. The researchers acknowledge funding from the Defense Threat Reduction Agency and the Defense Advanced Research Projects Agency.

The Institute of Optics is part of the University of Rochester's Hajim School of Engineering and Applied Sciences.

Media Contact

Leonor Sierra
lsierra@ur.rochester.edu
585-276-6264

 @UofR

http://www.rochester.edu 

Leonor Sierra | EurekAlert!

More articles from Physics and Astronomy:

nachricht NASA's James Webb Space Telescope completes final cryogenic testing
21.11.2017 | NASA/Goddard Space Flight Center

nachricht Previous evidence of water on mars now identified as grainflows
21.11.2017 | US Geological Survey

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Previous evidence of water on mars now identified as grainflows

21.11.2017 | Physics and Astronomy

NASA's James Webb Space Telescope completes final cryogenic testing

21.11.2017 | Physics and Astronomy

New catalyst controls activation of a carbon-hydrogen bond

21.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>