Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Final proof for optimal encoding strategies in optical communication

24.09.2014

MPQ theorist proves that Gaussian encoding guarantees minimum output entropy and hence ultimate capacity of optical communication channels.

The massive transfer of data over the Internet that is vital to today’s economy in our information society would not be possible without the crucial role played by fibre optics communication. Every time a node of the Internet sends information, it encodes a sequence of digital bits composing the message into light pulses.

These light pulses are later sent through an optical fibre to a receiving node that converts the light signal back to the original sequence of bits. The increase demand for higher data transfer raises the natural question on what are the fundamental physical limits to the information transmission rate over optical links.

Raul García-Patrón, former member of the Theory Division of Professor Ignacio Cirac at the Max Planck Institute of Quantum Optics, with collaborators from Pisa, Brussels and Moscow, has recently answered this question (Nature Photonics, 21 September 2014), concluding a research program that started during his Humboldt postdoctoral fellowship at the MPQ between the years 2011 and 2013.

It has been known since the pioneering work of Albert Einstein that light is composed at its smallest scale by quantum particles called photons. Therefore, a definitive answer to the question on the ultimate limits to optical communication needs to consider the quantum nature of light.

It was already at the beginning of the 1960s, after the development of the laser together with the development of the modern quantum theory of light, when the question on the fundamental physical limits to the information transmission rate over optical links was raised. But it was only a few decades later, at the birth of quantum communication theory at the end of the 1990s, that the right tools necessary to answer this question were developed by the pioneering work of Professor Alexander Holevo (co-author of this manuscript).

Subsequent work conjectured that the optimal strategy to send information over optical communication lines does not need the generation of highly complex quantum states, but simple light pulses generated by currently existing lasers are sufficient to reach the optimal communication rates. But no definitive answer had been given since then.

In a previous work in 2012 (Phys. Rev. Lett. 108, 110505, 2012), Raul García-Patrón (working then at the Theory Division at MPQ), in collaboration with Carlos Navarrete-Benlloch (current member of the Theory Division) and other scientists from the Universite Libre de Bruxelles and Massachusetts Institute of Technology, showed that any realistic optical communication channel can be modelled by a concatenation of an ideal attenuation channel followed by an ideal process of amplification.

Therefore, the former conjecture on the optimal strategy to encode information could be reduced to a basic question: what is the minimum disorder, or entropy, that is added to the input signal by one of the most studied quantum optical processes, namely optical parametric amplification? “Entropy is a measure of disorder. Minimum output entropy of the channel measures how much the channel distorts the input state that you initially sent through the line”, Dr García-Patrón explains.

“The highest achievable bit rate is given by a function that is optimized by minimizing the output entropy of the channel. Intuitively it means you want to minimize the distortion the channel produces to your input signal.” Now the team of scientists were able to prove that a Gaussian encoding achieves minimum out-put entropy and hence provides the ultimate capacity of an optical communication channel.

Gaussian states are the most natural states of light. Gaussian channels that preserve the “Gaussianity” of the state are the most natural models of optical communication links, for example fibres or amplifiers. Following the roadmap that was suggested in its previous work (the Physical Review Letters mentioned above) Dr. Garcia-Patron and collaborators successfully solved this longstanding open problem exploiting some known properties of the amplifier channels in a novel way.

The solution may have implications in other fields of physics, as many physical systems are mathematically modelled by bosonic Gaussian states and channels, for example, thermodynamical processes of bosonic systems, the theory of entanglement in Hawking radiation in black-holes, or superconducting systems. However, a few questions remain that wait to be answered.

“We know that very simple states achieve an optimal encoding. But we do not know if the same holds for the decoding of the information”, says García-Patrón. “Our result just gives a proof of existence: we know there is a detector achieving our rate, but further research is needed to find a realistic optimal decoding that could be implemented. As far as future applications are concerned, a simple efficient decoding could be useful e.g. in regimes where the signals are extremely weak at the reception, as in earth to deep-space communication.” R. García-Patrón/O. Meyer-Streng

Original publication:

V. Giovannetti, R. García-Patrón, N. J. Cerf and A. S. Holevo
Ultimate classical communication rates of quantum optical channels by solving the Gaussian minimum-entropy conjecture
Nature Photonics, Advance Online Publication, 21 September 2014

Contact:

Dr. Raul Garcia-Patrón
BELSPO postdoctoral fellow
QuIC - Ecole Polytechnique de Bruxelles
Université Libre de Bruxelles
50 av. F. D. Roosevelt - CP 165/59
B-1050 Bruxelles, Belgium
Phone: +32 2 650 -2820 / Fax: -2941
E-mail: rgarciap@ulb.ac.be
http://quic.ulb.ac.be/members/rgarciap

Prof. Dr. Ignacio Cirac
Honorary Professor TU München
Director at the Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1, 85748 Garching, Germany
Phone: +49 (0)89 32 905 -705/-736 / Fax: -336
E-mail: ignacio.cirac@mpq.mpg.de
www.mpq.mpg.de/cirac

Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics,
Phone: +49 (0)89 32 905 -213
E-mail: olivia.meyer-streng@mpq.mpg.de

Dr. Olivia Meyer-Streng | Max-Planck-Institut

More articles from Physics and Astronomy:

nachricht Igniting a solar flare in the corona with lower-atmosphere kindling
29.03.2017 | New Jersey Institute of Technology

nachricht NASA spacecraft investigate clues in radiation belts
28.03.2017 | NASA/Goddard Space Flight Center

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: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Researchers shoot for success with simulations of laser pulse-material interactions

29.03.2017 | Materials Sciences

Igniting a solar flare in the corona with lower-atmosphere kindling

29.03.2017 | Physics and Astronomy

As sea level rises, much of Honolulu and Waikiki vulnerable to groundwater inundation

29.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>