Double-dot charge qubit and transport via dissipative cotunneling

TL;DR

This paper studies a charge qubit made of two coupled quantum dots affected by environmental noise, revealing two phases: a Kondo phase with entanglement and a local moment phase where noise suppresses conductance, introducing dissipative cotunneling.

Contribution

It demonstrates the existence of two distinct quantum phases in a dissipative charge qubit and introduces the concept of dissipative cotunneling governing transport.

Findings

Identification of Kondo and local moment phases influenced by noise.

Observation of conductance suppression in the local moment phase.

Introduction of dissipative cotunneling as a transport mechanism.

Abstract

We investigate transport through an exotic ``charge'' qubit composed of two strongly capacitively coupled quantum dots (QDs), each being independently connected to a side gate which in general exhibits a fluctuating electrostatic field ({\em i.e.}, Nyquist/Johnson noise). Two quantum phases are found: the ``Kondo'' phase where an orbital-Kondo entanglement emerges and a ``local moment'' phase in which the noise destroys the Kondo effect leaving the orbital spin unscreened and resulting in a clear suppression of the conductance. In the Kondo realm, the transfer of charge across the setting is accompanied by zero-point charge fluctuations in the two dissipative environments and then the I-V characteristics are governed by what we call ``dissipative cotunneling''.