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Quantum commitment secures data transfer

22 January 2013

How can Alice submit a sealed bid to Bob without needing to trust him (or watch him all the time)? Quantum technology can do it, CQT researchers show in a paper published in Nature Communications.

Image: Timothy Yeo / CQT, NUS

This assembly of lasers, lenses, mirrors and crystals creates pairs of quantum-entangled photons

Photo: CQT, NUS

Many scenarios in business and communication require that two parties share information without either being sure if they can trust the other. Examples include secure auctions and identification at automated teller machines (ATMs). Researchers at the Centre for Quantum Technologies (CQT) at NUS are developing technologies that exploit the quantum interactions of the subatomic world to solve this problem.

In a paper published 27 December 2012 in Nature Communications, CQT researchers report the world's first demonstration of a "secure bit commitment" technology. The demonstration used quantum-entangled photons, which are the particles of light.

Secure bit commitment is equivalent to making a sealed bid in an auction. The bidders must commit to an amount they will pay, and each should remain the only one who knows what the amount is until all the bids are revealed.

Traditional solutions to this problem - think sealed envelopes or data held by a third party - always depend on trust. Indeed, classical communication alone has proven that no existing solution can totally protect the bidder and the bid receiver from unscrupulous behaviour. However, by harnessing quantum phenomena, the need for trust can be eliminated.

In the CQT experiment, the bid is encoded in entangled photons in such a way that it could only be completely decoded with instructions from the bidder. But the bid receiver can deduce enough about the bid from the encoded photons to know if the bidder tries to cheat when sending the decoding instructions, say, by using a different decoding.

The research was led by two Principal Investigators at CQT: Assistant Professor Stephanie Wehner, who had earlier proposed a key theoretical requirement for secure bit commitment - that anyone trying to cheat has limited ability to store quantum photons ("noisy storage") - and Professor Christian Kurtsiefer, whose experimental group has expertise in creating entangled photon pairs.

This first demonstration was a proof-of-concept, using 250,000 photon pairs to commit one bit of information. Dr Wehner said: "In the future, it would be exciting to see handheld devices based on integrated optics implementing more complex protocols in the real world. We've learned a few things about what the requirements for such set-ups should be from our experiment, and it should in principle be possible although it's still further off."

Other security problems in communication and computation can also be tackled with quantum phenomena. For example, CQT Senior Research Fellow Joe Fitzsimons last year demonstrated technology that provides secure quantum "cloud" computing.

See for more details.

By Centre for Quantum Technologies