1.II.15B

Quantum Mechanics
Part IB, 2006

Let V1(x)V_{1}(x) and V2(x)V_{2}(x) be two real potential functions of one space dimension, and let aa be a positive constant. Suppose also that V1(x)V2(x)0V_{1}(x) \leqslant V_{2}(x) \leqslant 0 for all xx and that V1(x)=V2(x)=0V_{1}(x)=V_{2}(x)=0 for all xx such that xa|x| \geqslant a. Consider an incoming beam of particles described by the plane wave exp(ikx)\exp (i k x), for some k>0k>0, scattering off one of the potentials V1(x)V_{1}(x) or V2(x)V_{2}(x). Let pip_{i} be the probability that a particle in the beam is reflected by the potential Vi(x)V_{i}(x). Is it necessarily the case that p1p2p_{1} \leqslant p_{2} ? Justify your answer carefully, either by giving a rigorous proof or by presenting a counterexample with explicit calculations of p1p_{1} and p2p_{2}.