It's not a real one. It uses just this http://en.wikipedia.org/wiki/Quantum_tunnelling. A real Quantum computer is expected in the next 30-50 years.
“The paper, which first appeared as a preprint earlier this year, concludes that the processor – built by the controversial Canadian firm D-Wave Systems – offers no advantage over a conventional computer when it is used to solve a benchmark computing problem.”
http://physicsworld.com/cws/article/news/2014/jun/20/is-d-wave-quantum-computer-actually-a-quantum-computer