Two-particle dark state cooling of a nanomechanical resonator

TL;DR

This paper explores how nanomechanical resonators can be cooled to their ground state using quantum dots and dark states, revealing that two-electron dark states enable effective cooling even with identical quantum dots, and that switching between single and two-electron states alters the cooling frequency.

Contribution

It introduces a novel two-electron dark state mechanism for cooling nanomechanical resonators, expanding the understanding of quantum dot interactions in cooling processes.

Findings

Two-electron dark states enable ground state cooling with identical quantum dots.

Detuning of energy levels is crucial for effective single-electron dark state cooling.

Switching from single to two-electron dark states changes the cooling frequency significantly.

Abstract

The steady-state cooling of a nanomechanical resonator interacting with three coupled quantum dots is studied. General conditions for the cooling to the ground state with single and two-electron dark states are obtained. The results show that in the case of the interaction of the resonator with a single-electron dark state, no cooling of the resonator occurs unless the quantum dots are not identical. The steady-state cooling is possible only if the energy state of the quantum dot coupled to the drain electrode is detuned from the energy states of the dots coupled to the electron source electrode. The detuning has the effect of unequal shifting of the effective dressed states of the system that the cooling and heating processes occur at different frequencies. For the case of two electrons injected to the quantum dot system, the creation of a two-particle dark state is established to be possible with spin-antiparallel electrons. The results predict that with the two-particle dark state, an effective cooling can be achieved even with identical quantum dots subject of an asymmetry only in the charging potential energies coupling the injected electrons. It is found that similar to the case of the single-electron dark state, the asymmetries result in the cooling and heating processes to occur at different frequencies. However, an important difference between the single and two-particle dark state cases is that the cooling process occurs at significantly different frequencies. This indicates that the frequency at which the resonator could be cooled to its ground state can be changed by switching from the one-electron to the two-electron Coulomb blockade process.