Population switching and charge sensing in quantum dots: A case for a quantum phase transition

TL;DR

This paper investigates how population switching in quantum dots can be a smooth crossover or an abrupt quantum phase transition depending on measurement setup, linking many-body effects and phase transitions.

Contribution

It demonstrates that population switching is generally smooth but can become a first-order quantum phase transition with an additional lead, connecting many-body phenomena to quantum phase transitions.

Findings

Population switching is typically smooth, not abrupt.

Adding a third lead can induce a first-order quantum phase transition.

The transition is related to the interplay of Mahan mechanism and Anderson orthogonality catastrophe.

Abstract

A broad and a narrow level of a quantum dot connected to two external leads may swap their respective occupancies as a function of an external gate voltage. By mapping this problem onto a multi-flavored Coulomb-gas we show that such population switching is not abrupt. However, trying to measure it by adding a third electrostatically coupled lead may render this switching an abrupt first order quantum phase transition. This is related to the interplay of the Mahan mechanism versus the Anderson orthogonality catastrophe, in similitude to the Fermi edge singularity. A concrete setup for experimental observation of this effect is also suggested.