Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Unforgeable quantum credit cards in sight

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, 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


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

Dr. Fernando Pastwawski
Max-Planck-Institute of Quantum Optics
Phone: +49 (0) 89 / 32 905 -639
Fax: +49 (0) 89 / 32 905 -336

Dr. Olivia Meyer-Streng
Max-Planck-Institute of Quantum Optics
Press and Public Relations
Phone: +49 (0) 89 / 32 905 -213

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:

More articles from Physics and Astronomy:

nachricht First results of NSTX-U research operations
26.10.2016 | DOE/Princeton Plasma Physics Laboratory

nachricht Scientists discover particles similar to Majorana fermions
25.10.2016 | Chinese Academy of Sciences Headquarters

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: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Greater Range and Longer Lifetime

26.10.2016 | Power and Electrical Engineering

VDI presents International Bionic Award of the Schauenburg Foundation

26.10.2016 | Awards Funding

3-D-printed magnets

26.10.2016 | Power and Electrical Engineering

More VideoLinks >>>