443 research outputs found
Comment on "Quantum Control and Entanglement in a Chemical Compass"
In this comment we show that the avian compass entanglement considerations of
J. Cai, G. G. Guerreschi and H. J. Briegel (Phys. Rev. Lett. 104, 220502
(2010)) result in unphysical predictions on the magnetic sensitivity of this
biochemical sensor. As well known from a series of papers on precision
measurements and detailed derivations of standard quantum limits, not taking
into account decoherence results in an overestimate of the entanglement
lifetime, and this is the case at hand. The entanglement lifetime is wrongly
assumed by the authors to be independent of the reaction time (the inverse of
the recombination rate) and hence it is grossly overestimated. This is so
because the spin coherence lifetime is limited by the reaction time, and the
entanglement lifetime cannot be any longer.Comment: 1 pages, 1 figur
Quantum relative entropy shows singlet-triplet coherence is a resource in the radical-pair mechanism of biological magnetic sensing
Radical-pair reactions pertinent to biological magnetic field sensing are an
ideal system for demonstrating the paradigm of quantum biology, the exploration
of quantum coherene effects in complex biological systems. We here provide yet
another fundamental connection between this biochemical spin system and quantum
information science. We introduce and explore a formal measure quantifying
singlet-triplet coherence of radical-pairs using the concept of quantum
relative entropy. The ability to quantify singlet-triplet coherence opens up a
number of possibilities in the study of magnetic sensing with radical-pairs. We
first use the explicit quantification of singlet-triplet coherence to
affirmatively address the major premise of quantum biology, namely that quantum
coherence provides an operational advantage to magnetoreception. Secondly, we
use the concept of incoherent operations to show that incoherent manipulations
of nuclear spins can have a dire effect on singlet-triplet coherence when the
radical-pair exhibits electronic-nuclear entanglement. Finally, we unravel
subtle effects related to exchange interactions and their role in promoting
quantum coherence.Comment: 11 pages, 5 figure
Quantum Dynamics of Radical-Ion-Pair Reactions
Radical-ion-pair reactions were recently shown to represent a rich
biophysical laboratory for the application of quantum measurement theory
methods and concepts, casting doubt on the validity of the theoretical
treatment of these reactions and the results thereof that has been at the core
of spin chemistry for several decades now. The ensued scientific debate,
although exciting, is plagued with several misconceptions. We will here provide
a comprehensive treatment of the quantum dynamics of radical-ion-pair
reactions, generalizing our recent work and elaborating on the analogy with the
double-slit experiment having partial "which-path" information. This analogy
directly leads to the general treatment of radical-ion pair reactions covering
the whole range between the two extremes, that of perfect singlet-triplet
coherence and that of complete incoherence.Comment: 11 pages, 6 figure
The radical-pair mechanism as a paradigm for the emerging science of quantum biology
The radical-pair mechanism was introduced in the 1960's to explain
anomalously large EPR and NMR signals in chemical reactions of organic
molecules. It has evolved to the cornerstone of spin chemistry, the study of
the effect electron and nuclear spins have on chemical reactions, with the
avian magnetic compass mechanism and the photosynthetic reaction center
dynamics being prominent biophysical manifestations of such effects. In recent
years the radical-pair mechanism was shown to be an ideal biological system
where the conceptual tools of quantum information science can be fruitfully
applied. We will here review recent work making the case that the radical-pair
mechanism is indeed a major driving force of the emerging field of quantum
biology.Comment: 22 pages, 13 figure
Quantum measurement corrections to CIDNP in photosynthetic reaction centers
Chemically induced dynamic nuclear polarization is a signature of spin order
appearing in many photosynthetic reaction centers. Such polarization,
significantly enhanced above thermal equilibrium, is known to result from the
nuclear spin sorting inherent in the radical pair mechanism underlying
long-lived charge-separated states in photosynthetic reaction centers. We will
here show that the recently understood fundamental quantum dynamics of
radical-ion-pair reactions open up a new and completely unexpected venue
towards obtaining CIDNP signals. The fundamental decoherence mechanism inherent
in the recombination process of radical pairs is shown to produce nuclear spin
polarizations on the order of times or more higher than the thermal
equilibrium value at earth's magnetic field relevant to natural photosynthesis.
This opens up the possibility of a fundamentally new exploration of the
biological significance of high nuclear polarizations in photosynthesis.Comment: 7 pages, 4 figure
Revealing the properties of the radical-pair magnetoreceptor using pulsed photo-excitation timed with pulsed rf
The radical-pair mechanism is understood to underlie the magnetic navigation
capability of birds and possibly other species. Experiments with birds have
provided indirect and in cases conflicting evidence on the actual existence of
this mechanism. We here propose a new experiment that can unambiguously
identify the presence of the radical-pair magnetoreceptor in birds and unravel
some of its basic properties. The proposed experiment is based on modulated
light excitation with a pulsed laser, combined with delayed radio-frequency
magnetic field pulses. We predict a resonance effect in the birds' magnetic
orientation versus the rf-pulse delay time. The resonance's position reflects
the singlet-triplet mixing time of the magnetoreceptor.Comment: 5 pages, 5 figure
Quantum Information Processing in the Radical-Pair Mechanism: Haberkorn theory violates the Ozawa entropy bound
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.Comment: 8 pages, 3 figure
Retrodictive derivation of the radical-ion-pair master equation and Monte-Carlo simulation with single-molecule quantum trajectories
Radical-ion-pair reactions, central in photosynthesis and the avian magnetic
compass mechanism, have recently shown to be a paradigm system for applying
quantum information science in a biochemical setting. The fundamental quantum
master equation describing radical-ion-pair reactions is still under debate. We
here use quantum retrodiction to produce a rigorous refinement of the theory
put forward in Phys. Rev. E {\bf 83}, 056118 (2011). We also provide a rigorous
analysis of the measure of singlet-triplet coherence required for deriving the
radical-pair master equation. A Monte-Carlo simulation with single-molecule
quantum trajectories supports the self-consistency of our approach.Comment: 12 pages, 8 figure
Quantum Measurement Theory Explains the Deuteration Effect in Radical-Ion-Pair Reactions
It has been recently shown that radical-ion pairs and their reactions are a
paradigm biological system manifesting non-trivial quantum effects, so far
invisible due to the phenomenological description of radical-ion-pair reactions
used until now. We here use the quantum-mechanically consistent master equation
describing magnetic-sensitive radical-ion-pair reactions to explain
experimental data [C. R. Timmel and K. B. Henbest, Phil. Trans. R. Soc. Lond. A
{\bf 362}, 2573 (2004); C. T. Rodgers, S. A. Norman, K. B. Henbest, C. R.
Timmel and P. J. Hore, J. Am. Chem. Soc. {\bf 129} 6746 (2007)] on the effect
of deuteration on the reaction yields. Anomalous behavior of radical-ion-pair
reactions after deuteration, i.e. data inconsistent with the predictions of the
phenomenological theory used so far, has been observed since the 70's and has
remained unexplained until now.Comment: 4 pages, 4 figure
The Jones-Hore theory of radical-ion-pair reactions is not self-consistent
It is shown that the master equation introduced by Jones & Hore and purported
to describe radical-ion-pair reactions is not self-consistent.Comment: 2 pages, published versio
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