Hosten & Kwiat

By combining quantum computation and quantum interrogation, scientists at the University of Illinois at Urbana-Champaign have found an exotic way of determining an answer to an algorithm – without ever running the algorithm.

Using an optical-based quantum computer, a research team led by physicist Paul Kwiat has presented the first demonstration of “counterfactual computation,” inferring information about an answer, even though the computer did not run.

“It seems absolutely bizarre that counterfactual computation – using information that is counter to what must have actually happened – could find an answer without running the entire quantum computer,” said Kwiat, ”but the nature of quantum interrogation makes this amazing feat possible.”

Sometimes called interaction-free measurement, quantum interrogation is a technique that makes use of wave-particle duality (in this case, of photons) to search a region of space without actually entering that region of space.

“In a sense, it is the possibility that the algorithm could run which prevents the algorithm from running,” Kwiat said. “That is at the heart of quantum interrogation schemes, and to my mind, quantum mechanics doesn’t get any more mysterious than this.”

Although I still don’t understand everything these lads are talking about — they surely look like they should be part of the DU Army.

Update: I received a nice email from Professor Kwiat trying to help me along to better understanding of his work. I’m afraid my math isn’t going to progress at this stage. He did make it clear that almost every article written about this project fell short in offering a complete explanation.