Elitzur–Vaidman bomb tester

Graduate Lunch Seminar, Pennsylvania State University

One often says that in quantum mechanics a measurement will in general change the state of the system – in contrast to classical physics. However, in this talk I will present an example where quantum mechanics can actually extract information from a system without changing it.
Imagine a bomb factory that produces bombs with super-high sensitive triggers – so sensitive that a single photon interaction is enough to make it explode. However, the production facility is not completely reliable, so that some bombs may end up without any trigger. Imagine further all bombs are stored in complete darkness and vacuum to prevent them from exploding. How can we check if a bomb has a trigger or not? While this seems classically completely impossible, I will present a procedure using quantum mechanics in which we can test the bomb, while making the probability that a bomb explodes arbitrarily small.