Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Unforgeable quantum credit cards in sight

02.10.2012
A team of physicists at Max-Planck-Institute of Quantum Optics, Harvard University, and California Institute of Technology develops a scheme for noise tolerant and yet safely encrypted quantum tokens.

Whoever has paid a hotel bill by credit card knows about the pending danger: given away the numbers of the card, the bank account and so on, an adversary might be able to forge a duplicate, take all the money from the account and ruin the person.


Figure: Illustration of a quantum bill
© background by vektorportal.com, collage by F. Pastwaski

On the other hand, as first acknowledged by Stephen Wiesner in 1983, nature provides ways to prevent forging: it is, for example, impossible to clone quantum information which is stored on a qubit. So why not use these features for the safe verification of quantum money?

While the digits printed on a credit card are quite robust to the usual wear and tear of normal use in a wallet, its quantum information counterparts are generally quite challenged by noise, decoherence and operational imperfections. Therefore it is necessary to lower the requirements on the authentication process. A team of physicists at Max-Planck-Institute of Quantum Optics (Garching), Harvard University (Cambridge, USA), and California Institute of Technology (Pasadena, USA) has demonstrated that such protocols can be made tolerant to noise while ensuring rigorous security at the same time (Proceedings of the National Academy of Science (PNAS), 18 September, 2012).

On the one hand, the properties of quantum information make it ideal for preventing any kind of forgery. On the other hand, everyday life conditions make it virtually impossible to perfectly store quantum bits of information due to the fragility of their physical carriers which could be individual nuclei. Researchers under the direction of Prof. Ignacio Cirac, director at MPQ and head of the Theory Division, and Prof. Mikhail Lukin (Harvard University) have focused on both improving storage quality and providing protocols which accommodate for such real-world imperfections. In order to do so, the verification process for such protocols must condone a certain amount of quantum bit failures. Relaxing the requirements for verification enhances the ability for a dishonest user to forge a quantum token. This interplay is addressed by the scientists by setting a tolerance threshold which admits a certain amount of noise while guaranteeing high security against fraudulent copies. As Dr. Fernando Pastawski (MPQ), who has worked on this topic in his doctoral thesis, was able to demonstrate, such thresholds are found for two kinds of “quantum token” protocols. In the first protocol, quantum information must be physically transferred back to the verifier who can then asses its validity directly. In contrast, the second protocol involves indirect verification by having the verifier communicate with the holder who locally measures constituent qubit memories.

In both approaches, the bank issues a token and sends it to the holder. The “identity” of the token can be encoded on photons transmitted via an optical fibre or on nuclear spins in a solid memory transferred to the holder. However, only the bank stores a full classical description of these quantum states.

In the approach denoted by “quantum ticket”, the holder has to return the token to the bank or another trusted verifier for validation. The verifier is willing to tolerate a certain fraction of errors which should be enough to accommodate the imperfections associated with encoding, storage and decoding of individual quantum bits. The only information returned to the holder is whether the ticket has been accepted or rejected. Thus it is “consumed” and no longer available to the holder. The scientists show that through such an approach, both the likelihood of rejecting the token from an honest user and that of accepting a counterfeit can be made negligible.

The second approach is the “classical verification quantum ticket”. In some cases it may be impossible that the quantum tickets are given back to the bank physically. Here the holder has to validate his quantum token remotely – by answering challenge questions. The group considers a scheme where the quantum information is organized in blocks of qubit pairs. A non-revealing challenge question consists of requesting the holder to use a specific measurement basis for each block. By doing so, the holder is capable of providing a correct answer, but the token is consumed. This excludes the possibility for a dishonest user to cheat by answering complementary questions. As before, the given tolerance threshold determines the number of correct answers that is necessary for the verification of the token. The block structure used for the tokens allows exponentially suppressing the undesired capability of a dishonest holder to answer two complementary questions while assuring a true holder’s token will be authenticated with a very high probability.

For both protocols a realistic noise tolerance can be achieved. “We can deduce from theory that on average no more than 83% of the secret digits may be duplicated correctly by a counterfeiter. Under realistic conditions, we can assume that an honest participant should be able to recover 95% of the digits. If now the verifier sets the tolerance level to 90%, it will be almost impossible to accept fraudulent tokens or to reject an authentic holder,” Dr. Pastawski explains.

The protocols could in principle be demonstrated by using single qubits, e.g. single photons which carry the information in their polarization state, or single nuclei where the quantum information is encoded in their spin state. “However, in order to reach the time scales necessary for relevant applications, good qubit memories are needed. We have recently achieved storage times of one second for single qubits at room temperature, which is a big step, but not yet sufficient,” Fernando Pastawski concedes. The quantum token presented here could serve as a primitive to construct quantum money – that can change hands several times – or even quantum credit cards that are unforgeable and hence immune to fraudulent charges. “I expect to live to see such applications become commercially available. However quantum memory technology still needs to mature for such protocols to become viable,” the scientist adds. [F. Pastawski/O. Meyer-Streng]

Original publication:
Fernando Pastawski, Norman Y. Yao, Liang Jiang, Mikhail D. Lukin, and J. Ignacio Cirac
“Unforgeable noise-tolerant quantum tokens”
Proceedings of the National Academy of Science (PNAS), 18 September, 2012

Contact:

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

Dr. Fernando Pastwawski
Max-Planck-Institute of Quantum Optics
Hans-Kopfermann-Straße
Phone: +49 (0) 89 / 32 905 -639
Fax: +49 (0) 89 / 32 905 -336
E-mail: fernando.pastawski@mpq.mpg.de

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

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:
http://www.mpq.mpg.de

More articles from Physics and Astronomy:

nachricht A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne

nachricht Quantum thermometer or optical refrigerator?
23.06.2017 | National Institute of Standards and Technology (NIST)

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: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>