The problem to be solved was simple: "what is the prime factors of the number 15." But it was the method that was neat: physicists did it with quantum calculation!

Professor Andrew White, from UQ’s Centre for Quantum Computer Technology together with colleagues from the University of Toronto in Canada, said by manipulating quantum mechanically entangled photons – the fundamental particles of light – the prime factors of the number 15 were calculated.

“Prime numbers are divisible only by themselves and one, so the prime factors of 15 are three and five,” Professor White said.

“Although the answer to this problem could have been obtained much more quickly by querying a bright eight-year-old, as the number becomes bigger and bigger the problem becomes more and more difficult.

“What is difficult for your brain is also difficult for conventional computers. This is not just a problem of interest to pure mathematicians: the computational difficulty of factoring very large numbers forms the basis of widely used internet encryption systems.”

Ben Lanyon, UQ doctoral student and the research paper’s first author, said calculating the prime factors of 15 was a crucial step towards calculating much larger numbers, which could be used to crack cryptographic codes that are unbreakable using conventional computers.

Link 

Wikipedia article about quantum computer