  Quantum particles move in strange ways, even when they propagate freely in
space. As a result of the uncertainty principle, it is not possible to control
the initial conditions of particle emission in such a way that the particle
will definitely pass through two precisely defined positions along its path,
even if it is possible to line up the two positions with the emitter. However,
there is also an upside to the quantum mechanical laws of motion: constructive
quantum interferences can actually raise probabilities to values higher than
those permitted by classical causality. Here, it is shown that conventional
interferometric methods can be used to prepare photons in a quantum state in
which a non-vanishing fraction of particles will hit both of two possible
targets, even though the direct line-of-sight connecting the two targets is
blocked at the source. The demonstration of the effect is complicated by the
uncertainty principle because the physical detection of a particle at one
target disturbs the motion of the particle, making it impossible to determine
whether the initial state of motion would have allowed the particle to hit the
other target or not. It is nonetheless possible to determine the minimal
fraction of "magic bullet" particles that must have hit both targets by showing
that the number of particles hitting target A is larger than the number of
particles missing target B. Quantum interference effects can thus be used to
optimize the path of particles in free space beyond the classical limit of
motion along a straight line.
