Quantum Information Processing in the Radical-Pair Mechanism: Haberkorn theory violates the Ozawa entropy bound

TL;DR

This paper demonstrates that the traditional Haberkorn theory for radical-pair reactions violates fundamental quantum entropy bounds, while a newer quantum measurement-based theory adheres to these bounds and better explains magnetic field effects.

Contribution

It identifies a fundamental violation in the Haberkorn theory and proposes a quantum measurement-based framework that complies with quantum entropy bounds and explains magnetic effects.

Findings

Haberkorn theory violates Ozawa entropy bound.

Quantum measurement-based theory satisfies entropy bounds.

New approach explains magnetic-field effects beyond reaction yields.

Abstract

Radical-ion-pair reactions, central for understanding the avian magnetic compass and spin transport in photosynthetic reaction centers, were recently shown to be a fruitful paradigm of the new synthesis of quantum information science with biological processes. We show here that the master equation so far constituting the theoretical foundation of spin chemistry violates fundamental bounds for the entropy of quantum systems, in particular the Ozawa bound. In contrast, a recently developed theory based on quantum measurements, quantum coherence measures, and quantum retrodiction, thus exemplifying the paradigm of quantum biology, satisfies the Ozawa bound as well as the Lanford-Robinson bound on information extraction. By considering Groenewold information, the quantum information extracted during the reaction, we reproduce the known and unravel other magnetic-field effects not conveyed by reaction yields.