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.