Detecting single-electron tunneling involving virtual processes in real time

TL;DR

This paper employs time-resolved charge detection to investigate virtual tunneling processes and cotunneling in double quantum dots, revealing the equivalence with molecular states and analyzing inelastic cotunneling effects.

Contribution

It demonstrates the experimental observation of virtual tunneling, cotunneling, and their relation to molecular states in quantum dots using time-resolved techniques.

Findings

Cotunneling probability relates to time-energy uncertainty.

Delocalization leads to molecular state formation.

Shot noise analysis in cotunneling regime.

Abstract

We use time-resolved charge detection techniques to probe virtual tunneling processes in a double quantum dot. The process involves an energetically forbidden state separated by an energy $\delta$ from the Fermi energy in the leads. The non-zero tunneling probability can be interpreted as cotunneling, which occurs as a direct consequence of time-energy uncertainty. For small energy separation the electrons in the quantum dots delocalize and form molecular states. In this regime we establish the experimental equivalence between cotunneling and sequential tunneling into molecular states for electron transport in a double quantum dot. Finally, we investigate inelastic cotunneling processes involving excited states of the quantum dots. Using the time-resolved charge detection techniques, we are able to extract the shot noise of the current in the cotunneling regime.