Scientists cast doubt on renowned uncertainty principle

This is a general method for measuring the
precision and disturbance of any system.
The system is weakly measured before the
measurement apparatus and then strongly
measured afterwords. Credit: Lee
Rozema, University of Toronto

Scientists cast doubt on renowned uncertainty principle
Sept 7, 2012 | Phys.org

The principle has bedeviled quantum physicists for nearly a century, until recently, when researchers at the University of Toronto demonstrated the ability to directly measure the disturbance and confirm that Heisenberg was too pessimistic.

"We designed an apparatus to measure a property – the polarization – of a single photon. We then needed to measure how much that apparatus disturbed that photon," says Lee Rozema, a Ph.D. candidate in Professor Aephraim Steinberg's quantum optics research group at U of T, and lead author of a study published this week in Physical Review Letters.

"To do this, we would need to measure the photon before the apparatus but that measurement would also disturb the photon," Rozema says.

In order to overcome this hurdle, Rozema and his colleagues employed a technique known as weak measurement wherein the action of a measuring device is weak enough to have an imperceptible impact on what is being measured. Before each photon was sent to the measurement apparatus, the researchers measured it weakly and then measured it again afterwards, comparing the results. They found that the disturbance induced by the measurement is less than Heisenberg's precision-disturbance relation would require.

Read more at: http://phys.org/news/2012-09-scientists-renowned-uncertainty-principle.html#jCp