Why is the conductance quantized?

[wdlang]

according to the Landauer formula, the conductance is proportional to the transmission probability.

But the transmission probability is not quantized generally

So why is the conductance quantized?

 

[UltrafastPED]

Does this help: http://en.wikipedia.org/wiki/Conductance_quantum

Quantization of conductance only applies in special circumstances.

 

[wdlang]

Does this help: http://en.wikipedia.org/wiki/Conductance_quantum

Quantization of conductance only applies in special circumstances.

i now see.

So it is not as specular as magnetic quantization in superconductors