How to decide who keeps the car: Tossing quantum coins moves closer to reality

Nov 29, 2011

Alice and Bob have broken up and have moved as far away from each other as possible. But they still have something to sort out: who gets to keep the car. Flipping a coin while talking on the phone to decide who gets to keep it just won't work. There's no trust. Neither believes each other's result.

A paper published in Nature Communications by a team of researchers from Canada and Switzerland explores the concept of coin flipping in the context of that uses , so-called photons, to allow communication tasks in a manner that outperforms standard communication schemes.

To understand the researchers' approach, it helps to use an analogy that involves a safe. Bob flips a coin and sends the result of his coin flip, hidden in the safe, to Alice. Upon receiving Bob's safe, Alice sends the result of her own flip to Bob. Once received, Bob sends the key to Alice who unlocks the safe. Now, Alice and Bob both know each other's coin flip and, according to some previously agreed-upon rule, who will drive away with the car.

In a world made out of electronic bits, used for communication instead of safes, the physical safe is replaced by over email. This procedure is believed to be hard to break. Unfortunately, no one knows if this is truly a good safe. This would allow Alice to cheat by unlocking Bob's "safe" without awaiting his key, reading the secret, and choosing the result of her own flip in a way that ensures that she will keep the car.

But it's a different story with quantum communications.

"What we have shown here is the first implementation of quantum coin flipping in which a cheater can not take advantage of the fact that photons may get lost during transmission between Alice and Bob. All previous schemes could be broken by a cheater," says co-author Dr. Wolfgang Tittel, professor in the Institute for and the Department of Physics and Astronomy at the University of Calgary. The other co-authors are from the University of Calgary, Université de Montréal, École Polytechnique de Montréal and Université de Genève, in Switzerland.

The quantum coins in this study were tossed with one player being at the University of Calgary and the other player at the SAIT Polytechnic, roughly 5 km apart.

"The exchange of quantum bits instead of electronic bits prevents unrecognized cheating because we base our protocol on properties of nature, such as the impossibility to perfectly determine the quantum state of a single photon" say Dr. Félix Bussières, who did parts of his PhD studies at the University of Calgary, where the experiment was performed, before moving to Switzerland to take up a postdoctoral fellowship.

"Unfortunately, even in the world, coin flipping at a distance is not perfect either - it is still possible to cheat, at least to some extent. However, no party can fix the final outcome with certainty, and, if trying to cheat, risks being caught cheating."

Nevertheless, this demonstration has made the decision of who gets the car fairer.

Explore further: New research signals big future for quantum radar

Related Stories

Quantum Mechanical Con Game

May 05, 2008

For the first time, physicists have come up with a scheme that would allow a quantum mechanical expert to win every time in a con game with a victim who only knows about classical physics. Prior quantum cons have typically ...

Quantum eavesdropper steals quantum keys

Jun 20, 2011

( -- In quantum cryptography, scientists use quantum mechanical effects to encrypt and then communicate confidential information. Although quantum cryptography codes are unbreakable in principle, even the best ...

'Dead time' limits quantum cryptography speeds

Sep 28, 2007

Quantum cryptography is potentially the most secure method of sending encrypted information, but does it have a speed limit" According to a new paper by researchers at the National Institute of Standards and Technology and ...

Recommended for you

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

Precision gas sensor could fit on a chip

Feb 27, 2015

Using their expertise in silicon optics, Cornell engineers have miniaturized a light source in the elusive mid-infrared (mid-IR) spectrum, effectively squeezing the capabilities of a large, tabletop laser onto a 1-millimeter ...

A new X-ray microscope for nanoscale imaging

Feb 27, 2015

Delivering the capability to image nanostructures and chemical reactions down to nanometer resolution requires a new class of x-ray microscope that can perform precision microscopy experiments using ultra-bright ...

New research signals big future for quantum radar

Feb 26, 2015

A prototype quantum radar that has the potential to detect objects which are invisible to conventional systems has been developed by an international research team led by a quantum information scientist at the University ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (2) Nov 29, 2011
I always smile when I see a phrase like " photons...". Healthy skepticism or inappropriate idiom? Yes, that is the correct term for light quanta... *chuckle*

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.