  Elitzur and Vaidman have proposed a measurement scheme that, based on the
quantum superposition principle, allows one to detect the presence of an object
--- in a dramatic scenario, a bomb --- without interacting with it. It was
pointed out by Ghirardi that this interaction-free measurement scheme can be
put in direct relation with falsification tests of the macro-realistic
worldview. Here we have implemented the "bomb test" with a single atom trapped
in a spin-dependent optical lattice to show explicitly a violation of the
Leggett-Garg inequality --- a quantitative criterion fulfilled by
macro-realistic physical theories. To perform interaction-free measurements, we
have implemented a novel measurement method that correlates spin and position
of the atom. This method, which quantum mechanically entangles spin and
position, finds general application for spin measurements, thereby avoiding the
shortcomings inherent in the widely used push-out technique. Allowing
decoherence to dominate the evolution of our system causes a transition from
quantum to classical behavior in fulfillment of the Leggett-Garg inequality.
