Feedback-charging a metallic island

TL;DR

This paper explores a feedback-controlled quantum dot system that acts as a Maxwell demon, enabling electron transport against bias by using measurement-based feedback, with a focus on realistic detector modeling.

Contribution

It introduces a detailed model of feedback control in a quantum dot system, incorporating measurement errors and demonstrating Maxwell demon-like behavior.

Findings

Feedback can direct current against bias.

Measurement errors are quantitatively incorporated.

The system can charge the metallic island via feedback.

Abstract

We consider electronic transport through a single-electron quantum dot that is tunnel-coupled to an electronic lead and a metallic island. A background reservoir keeps the metallic island at a thermal state with the ambient temperature, while the charge accumulated on the island is reflected in a time-dependent chemical potential. Without feedback, a current would flow through the system until the chemical potentials of island and lead are equilibrated. A feedback loop can be implemented by a quantum point contact detecting the dot state, classical processing of the result and appropriate feedback actions on the electronic tunneling rates taken, with the objective to direct the current in a preferred direction. Since we directly take the detector counting statistics into account, this automatically includes measurement errors in the description. When mainly the rates are modified but hardly any energy is exchanged with the system, this feedback loop effectively implements a Maxwell demon, capable of transporting electrons against an electric bias and thereby charging the metallic island. Once the feedback protocol is stopped, the metallic island simply discharges. We find that a quantitative detector model may be useful for a realistic statistical description of feedback loops.