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The one-dimensional double delta function potential, , is perhaps the simplest example of a scattering problem exhibiting the phenomenon of resonance. As the scattering wavefunctions can be found in closed form, it constitutes a very useful textbook-style example.

The resonance can be thought of as arising from interference between paths that are reflected a different number of times between the two barriers. In this Demonstration, both the energy of the incoming particle and the spacing between the two barriers can be varied.

Snapshot 1: lowest order resonance, corresponding to approximately half a wavelength between the two barriers

Snapshot 2: increasing the separation between the barriers decreases the energy of resonant transmission: here is the third resonance for a wider double barrier

Snapshot 3: bringing the barriers together destroys the resonance effect: here the barriers are very close together and the transmission function is very close to that of a single barrier