Elementary Events of Electron Transfer in a Voltage-Driven Quantum Point Contact

We find that the statistics of electron transfer in a coherent quantum point contact driven by an arbitrary time-dependent voltage is composed of elementary events of two kinds: unidirectional one-electron transfers determining the average current and bidirectional two-electron processes contributing to the noise only. This result pertains at vanishing temperature while the extended Keldysh-Green’s function formalism in use also enables the systematic calculation of the higher-order current correlators at finite temperatures.

Figure 1

Schematic representation of elementary events: bidirectional (a), (b) and unidirectional (c). Shifts of the effective chemical potential in the left lead due to time-dependent voltage drive are indicated by shading. For periodic drive, the dc voltage component [panel (d), dash-dotted line] describes unidirectional charge transfer, while the ac component (dashed curve) describes bidirectional events affecting the noise and higher-order even cumulants.

Figure 2

The probability of elementary events for harmonic drive with amplitude $V_0$ (upper panel). With increasing amplitude more and more eigenvalues ${\alpha }_k$ come into play and contribute to transport. The derivative of the noise power with respect to $V_0$ (solid line) decomposed into contributions (dashed line) of elementary events (lower panel).