  The tunneling conductances of a quantum point contact and a magnetized atom
adsorbed on an insulating layer above a metallic substrate are obtained by
considering the coherent transport of the entangled and nonentangled Kondo
singlets, and these are compared with the experimental results. Spins of the
entangled Kondo singlet flow unidirectionally in a sequential up-and-down
manner. This transport does not follow linear response theory. The nonentangled
Kondo singlet performs resonant tunneling through a coherent transport channel
and yields coherent side peaks at a finite bias. The coherent transport channel
is formed by two electron reservoirs within a coherent region.
