Can Shot‐Noise Measurements Distinguish Between Coherent and Sequential Tunneling?

We have measured the shot noise of GaAs‐(Ga,Al)As double‐well resonant‐tunneling diodes in which the barrier between the wells is so narrow (1.5 nm) that there is a strong quantum‐mechanical coupling between the wells’ energy states. When compared with results in uncoupled double‐well structures, our experiments show that there is no significant difference between coupled‐ and uncoupled‐well diodes, thus casting doubt about calculations that predict that the amount of shot noise should depend on whether tunneling is sequential or coherent.