Breakdown of classical conservation of energy in a quantum wave-packet collision with a double barrier

A transient interference during the collision of a broad quantum particle wave packet with a properly chosen potential barrier suppresses, for energies well above the barrier top, the main incident momentum. This collision enhances the momenta below and above the central one, violating the classical conservation of energy. For the double square barrier the effect is due to the interference between three components (incident, transmitted, and interbarriers terms) and survives much longer than for the single barrier, facilitating its observation. A quantum optical realization, with two-level atoms and effective laser barriers is discussed.