Chinese researchers have created a hypothesis for a quantum cloning machine able to produce several copies of the state of a particle at atomic or sub-atomic scale, or quantum state, which if produced could have implications for quantum information processing methods such as encryption systems.

Quantum cloning is difficult because quantum mechanics laws only allow for an approximate copy—not an exact copy—of an original quantum state to be made, as measuring such a state prior to its cloning would alter it. In their study, they demonstrate that it may be possible to create four approximate copies of an initial quantum state, a process called asymmetric cloning.

The authors extended previous work that was limited to quantum cloning providing only two or three copies of the original state, a limitation because the quality of the approximate copy decreases as the number of copies increases. The authors were able to optimize the quality of the cloned copies, thus yielding four good approximations of the initial quantum state.

They have also demonstrated that their quantum cloning machine has the advantage of being universal and therefore is able to work with any quantum state, ranging from a photon to an atom.

Asymmetric quantum cloning has applications in analyzing the security of messages encryption systems, based on shared secret quantum keys. Two people will know whether their communication is secure by analyzing the quality of each copy of their secret key.

Any third party trying to gain knowledge of that key would be detected as measuring it would disturb the state of that key.

Published in EPJ D.