Olomouc Scientists First to Verify How Quantum Money Could Work

The beam divider is one of the key segments for optical quantum gates. Photo: Antonín Černoch
Thursday 13 April 2017, 8:57 – Text: Martina Šaradínová

Scientists from the Joint Laboratory of Optics and the Regional Centre of Advanced Technologies at Palacký University Olomouc have turned into money minters and forgers – only temporarily, though. They did not work, however, with paper money but with virtual quantum banknotes that could be represented as sequences of photons – that is, sorts of packets of light energy. Their endeavours have resulted in a unique study, and they have become the first scientists in the world who were able to verify the existence of quantum banknotes and test the possibilities of their copy-protection.

The idea of quantum money, to guarantee higher security, emerged in the 1970s. It is based on the rules of quantum mechanics, according to which quantum states can never be perfectly cloned. The transfer of quantum information is thus much safer than existing methods, and quantum money could protect financial transactions from cyber attacks. This hypothesis has now been experimentally verified by scientists from Olomouc in collaboration with their colleagues from Poland and Japan. The study appeared in the journal NPJ Quantum Information, published by Springer Nature.

“Our paper reported on the experimental quantum optical implementation of a quantum money protocol, which was experimentally tested regarding its resistance to quantum counterfeiting. We have tested several proposed quantum money schemes and shown which of them are even safe against forgery using optimal cloning machines,” said one of the authors, Karel Lemr.

Demand grows with development of quantum technologies

Quantum money has not been used in practice yet. One of the reasons is that quantum memories or purses that would store quantum states have not been developed. Nevertheless the developments in this area are progressing fast. “With the development of quantum technologies, demand for quantum money will grow. Quantum computers and other devices will be able to easily break the algorithms protecting digital financial transactions now. This safety issue could probably be solved by the implementation of quantum money – virtual banknotes encoded in the quantum states of single photons,” said another co-author, Antonín Černoch, in order to outline possible development.

Scientists could follow up on their previous findings from the area of quantum information processing, transfer and encryption. The core of the experiment was in the quantum cloner, a device that can make copies of quantum states, designed by Olomouc scientists for use in quantum computers and quantum cryptography. In this case, they used their cloner as a quantum copy machine. The cloner is a quantum gate, that is, a basic quantum circuit that is able to copy quantum states, even though perfect cloning is not possible – so it is only as good as the laws of nature allow.

Scientists simulated information transfer between banks

“Our paper also explores the success rate of the cloning process. Our previous device was constructed to make high fidelity copies, but the success rate of the copying was low, below 30 percent. With quantum money, however, you need at least one half of the photons to survive and reach the bank. Therefore we had to combine several cloning procedures in order to increase our success rate without going beyond the limit when a bank would consider the money damaged,” added Černoch.

Scientist simulated an information transfer between two banks in the laboratory, sending the photons experimentally over short distances. However, photons may reach a distance of dozens of kilometres via optical fibres, or kilometres in free space. Presently, UP scientists are exploring the quantum information transfer in networks. They have been testing various prototypes of communication networks and verifying their functionality.

Quantum mechanics, together with the theory of relativity, is considered one of the pillars of modern physics. In quantum mechanics, the state of microparticles is not described by their exact position and momentum, as in classical mechanics, but by their wave function, a complex of probabilities of many positions and momentums gained by a particle simultaneously in one instant.


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