Decades of experiments have verified the quirky（古怪的） laws of quantum theory again and again. So when scientists in Germany announced in 2012 an apparent violation of a fundamental law of quantum mechanics, a physicist at the University of Rochester was determined to find an explanation. "You don't destroy the laws of quantum mechanics that easily," said Robert Boyd, professor of optics and of physics at Rochester and the Canada Excellence Research Chair in Quantum Nonlinear Optics at the University of Ottawa.

In their 2012 version of the famous Young two-split experiment, Ralf Menzel and his colleagues at the University of Potsdam simultaneously determined a photon's path and observed high contrast interference fringes created by the interaction of waves from the two slits.

"This result was extremely surprising, as one of the basic tenets of quantum mechanics holds that there should be no quantum interference when it is known through which slit the particle (a photon in this case) had passed," said Boyd.

Inspired by these intriguing（有趣的） results, Boyd and his colleagues replicated the Menzel experiment. Their findings were recently published online in an early edition of the Proceedings of the National Academy of Sciences.

"The data of the Menzel experiment were very clean, so we weren't surprised to obtain the same initial result," said Boyd. "My coworkers and I asked what could explain this apparent violation of a key principle of quantum mechanics. What we found is that the resolution of the problem requires great subtly in the way that one needs to analyze the data for this type of measurement."