Propagation of ultrashort voltage pulses through a small quantum dot

TL;DR

This paper investigates how ultrashort voltage pulses propagate through a small quantum dot, revealing oscillatory and negative current phenomena at lower frequencies than traditional nanoelectronic systems, with potential experimental realization.

Contribution

It introduces a model for ultrashort pulse transport in quantum dots, predicting novel current behaviors and providing analytical and numerical validation at accessible frequencies.

Findings

Current oscillates with pulse amplitude for short pulses

Negative current flow against voltage drop predicted in ultrafast regime

Model aligns with experimental feasibility at lower frequencies

Abstract

The coherent transport of time-resolved ultrafast excitations in nanoelectronic interferometers is expected to exhibit an interesting interplay between the interferences and the time-dependent drive. However, the typical frequencies required to unlock this physics are in the THz range, making its observation challenging. In this work, we consider the propagation of the excitation generated by ultrashort voltage pulses through a small quantum dot, a system which we argue can display similar physics at significantly lower frequencies. We model the system with a single resonant level connected to two infinite electrodes subjected to a time-dependent voltage bias. For short pulses, we predict that the behaviour of the dot contrasts sharply with the long pulse (adiabatic) limit: the current actually oscillates with the amplitude of the voltage pulse. In the ultrafast limit, we predict that the current can even be negative, i.e. flow against the voltage drop. Our results are obtained by a combination of two approaches that are in quantitative agreement: explicit analytical expressions in the ultrafast and ultraslow limits and exact numerical simulations. We discuss the applicability of our findings and conclude that this system should be within reach of existing experimental platforms.