An electronic Maxwell demon in the coherent strong-coupling regime

TL;DR

This paper explores a quantum dot system with feedback control acting as a Maxwell demon, analyzing its behavior in strong coupling regimes and showing how measurement strength affects power generation and the demon interpretation.

Contribution

It extends the analysis of Maxwell demon-like feedback control to the strong-coupling regime using a fermionic reaction-coordinate mapping, revealing limitations of the demon interpretation.

Findings

Weak measurement allows feedback without transport blockade.

Strong coupling can require more energy than power produced.

Quantum Zeno effect suppresses transport under continuous measurement.

Abstract

We consider a feedback control loop rectifying particle transport through a single quantum dot that is coupled to two electronic leads. While monitoring the occupation of the dot, we apply conditional control operations by changing the tunneling rates between the dots and its reservoirs, which can be interpreted as the action of a Maxwell demon opening or closing a shutter. This can generate a current at equilibrium or even against a potential bias, producing electric power from information. While this interpretation is well-explored in the weak-coupling limit, we can address the strong-coupling regime with a fermionic reaction-coordinate mapping, which maps the system into a serial triple quantum dot coupled to two leads. There, we find that a continuous projective measurement of the central dot would lead to a complete suppression of electronic transport due to the quantum Zeno effect. In contrast, a microscopic model for the quantum point contact detector implements a weak measurement, which allows for closure of the control loop without inducing transport blockade. In the weak-coupling regime between the central dot and its leads, the energy flows associated with the feedback loop are negligible, and the information gained in the measurement induces a bound for the generated electric power. In contrast, in the strong coupling limit, the protocol may require more energy for opening and closing the shutter than electric power produced, such that the device is no longer information-dominated and can thus not be interpreted as a Maxwell demon.