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Electrons follow the energy landscape of the circuit, which is formed by the
network of interconnected quantum dots. With the voltage sources
one deforms the energy landscape and thus controls the transfer of
electrons. Depending on the material and size of the quantum dots, different
components of the energy are dominating. Metal quantum dots larger than 3 nm
in diameter and semiconductor quantum dots larger than 10 nm in diameter can
be described sufficiently with the classical electrostatic charging energy.
For smaller quantum dots the quantum confinement energy has to be taken into
account.
Electrons move preferably to lower points in the energy landscape. The
probability or rate of a transition from one location to another depends
exponentially on the energy difference the electron experiences. The
Coulomb blockade can be viewed as an electron trapped in a local minimum of the
energy landscape. Co-tunneling events transport electrons from one local minimum to
another lower lying minimum. Therefore, co-tunneling makes stable states instable
and introduces errors in device behavior.
Christoph Wasshuber