Experimental Realization of a Maxwell’s Demon Exploiting Quantum Information Flow: Toward Efficient Quantum Feedback Control

A research team from the theoretical group at the University of Tokyo and the experimental group at Harvard University has experimentally demonstrated a Maxwell’s demon that reduces thermodynamic entropy by exploiting quantum information flow on a silicon-vacancy center system under iterative measurement and feedback. By experimentally evaluating both information-theoretic and thermodynamic quantities, they verified the fundamental thermodynamic laws—the second law and the fluctuation theorem—in an iterative quantum feedback setup. These experiments were enabled by performing real-time feedback with high accuracy on a timescale shorter than the coherence time.
In addition, the team established a theoretical framework that quantifies the thermodynamic efficiency of feedback control based on the causal structure of the feedback. This framework makes it possible to characterize how non-Markovian feedback, which utilizes the whole history of past measurement outcomes, can enhance thermodynamic efficiency compared to Markovian feedback, which relies only on the most recent outcome. They further implemented a non-Markovian feedback protocol on the experimental platform and quantified the resulting enhancement in thermodynamic efficiency.

Caption: Schematic for the silicon-vacancy center system under iterative measurement and feedback

Papers 
Journal: Physical Review X
Title: Experimentally Probing Entropy Reduction via Iterative Quantum Information Transfer
Authors: Toshihiro Yada*, Pieter-Jan Stas*, Aziza Suleymanzade, Erik N. Knall, Nobuyuki Yoshioka, Takahiro Sagawa, and Mikhail D. Lukin. (*These authors contributed equally to this work.)
DOI: 10.1103/5lp2-9sps