Transport package
The main purpose of the qtcad.transport package is to describe
quantum transport in a QTCAD Device
object coupled to two electrons (or hole)
reservoirs, hereafter referred to as “source” and “drain”. There are two main
modules within the qtcad.transport package that achieve this goal.
First, the qtcad.transport.junction module models quantum transport
through a quantum dot in the Coulomb blockade regime and can therefore be used
to compute charge stability diagrams. However, this module cannot model other
transport mechanisms, such as the thermionic emission that arises in
field-effect transistors (FETs) under classical regimes of operation.
Second, the qtcad.transport.negf_poisson module models the
nonequilibrium quantum statistics and electrostatics arising in an arbitrary
two-probe device under a finite drain–source bias in a self-consistent manner.
Moreover, it can model transport under traditional transistor regimes of
operation (e.g. thermionic emission) as well as under regimes of operation
that are typically more relevant to devices used in quantum technology
(e.g. sequential tunneling). However, this module ignores electron–electron (or
hole–hole) interactions, and can therefore not capture Coulomb blockade
phenomena.
The first three tutorials of this section are based on the
qtcad.transport.junction module. In the first
tutorial, a master equation approach is used. In the second tutorial, an
approach based on the WKB approximation is used. In the third tutorial, a
computationally-efficient workflow is presented for charge stability diagram
calculations in double quantum dots.
The last tutorial of this section is based on the
qtcad.transport.negf_poisson module. It presents NEGF–Poisson
simulations of a FET including a quantum dot in the off state, the on state,
and the sequential tunneling regime.