= Quantum transport
Quantum transport studies the flow of <particles>, <electric charge> or <energy> when <quantum states>, their occupation and their <transmission probabilities> determine the flow. In a short <quantum wire>, transverse <quantum confinement> permits only discrete <transverse electronic modes>, even though motion along the wire remains possible.
The <Landauer formula> treats two contacts as reservoirs supplying incident <electrons>. Their different occupations drive an <electric current>; a <potential barrier> changes the <transmission probability> of each incident mode. At low <temperature>, opening one perfectly transmitted spin-resolved mode increases the <electrical conductance> by the <spin-resolved conductance quantum> $e^2/h$. <Quantum tunnelling>, <interference> and <Coulomb blockade> explain departures from a simple classical resistor picture.
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