  Electron transport through a nanoscale system is an inherently stochastic
quantum mechanical process. Electric current is a time series of electron
tunnelling events separated by random intervals. Thermal and quantum noise are
two sources of this randomness. In this paper, we used the quantum master
equation to consider the following questions: (i) Given that an electron has
tunnelled into the electronically unoccupied system from the source electrode
at some particular time, how long is it until an electron tunnels out to the
drain electrode to leave the system electronically unoccupied, where there were
no intermediate tunnelling events ("the" tunnelling path)? (ii) Given that an
electron has tunnelled into the unoccupied system from the source electrode at
some particular time, how long is it until an electron tunnels out to the drain
electrode to leave the system electronically unoccupied, where there were no
intermediate tunnelling events ("an" tunnelling path)? (iii) What are the
distributions of these times? We show that electron correlations suppress the
difference between "the" and "an" electron tunnelling paths.
