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Quantum biology – excitons in plant chromophores

John Healy

When a photon excites an electron within plant chromophores [1], the transport of energy (without transporting net electric charge) resembles an exciton [2] condensate.

“Chromophores … can pass energy between them in the form of excitons to a reaction center where energy can be used, kind of like a group of people passing a ball to a goal,” Anna Schouten, the study’s lead author, explained to Big Think.

Notes

[1] Wiki > Chromophore

A chromophore is the part of a molecule responsible for its color. … The chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.

See also Wiki > Chlorophyll – Chlorophyll molecules are arranged in and around photosystems that are embedded in the thylakoid membranes of chloroplasts.

And Wiki > Resonance energy transfer – a mechanism describing energy transfer between two light-sensitive molecules (chromophores).

[2] Wiki > Exciton (electron-hole pairs as integer-spin particles)

When a molecule absorbs a quantum of energy that corresponds to a transition from one molecular orbital to another molecular orbital, the resulting electronic excited state is also properly described as an exciton. … Molecular excitons have several interesting properties, one of which is energy transfer … whereby if a molecular exciton has proper energetic matching to a second molecule’s spectral absorbance, then an exciton may transfer (hop) from one molecule to another.

Related posts

Plant chloroplasts
Seen through a microscope, chlorophyll is concentrated within organisms in structures called chloroplasts – shown here grouped inside plant cells.

[(Wiki) Creative Commons Attribution-Share Alike 3.0 Unported license]

One thought on “Quantum biology – excitons in plant chromophores”

  1. Visualization of quantum interactions always is welcome. But what’s a coherence map? … in a snapshot … interpreting theoretical calculations … an illustration of the reduced density matrix … to identify the energy transfer pathways …

    • Phys.org > “Quantum visualization technique gives insight into photosynthesis” by University of Illinois Grainger College of Engineering (June 6, 2023)

    Systems obeying quantum mechanics are notoriously difficult to visualize, but researchers at the University of Illinois Urbana-Champaign have developed an illustration technique that displays quantum features in an easy-to-read diagram called a coherence map. The researchers used these maps to study the quantum mechanisms that underlay photosynthesis, …

    In a study published in The Journal of Physical Chemistry Letters, [Nancy Makri, a professor of chemistry at the U. of I] Makri’s research group applied coherence maps to analyze earlier computer simulations of photosynthesizing bacteria in a new way. The researchers studied the molecular complex [an outer ring and an inner ring of molecules] that “harvests” sunlight, absorbing it and transferring its energy to a chemical reaction site where carbon dioxide and water are processed. Coherence maps not only clearly displayed how energy was transferred to the reaction site [by the motions of the atoms in the molecules], but they gave a clear quantum explanation for the transfer.

    See also:

    Huh? Huh!

    • PubMed > “Time-Evolving Quantum Superpositions in Open Systems and the Rich Content of Coherence Maps” by Reshmi Dani, Nancy Makri (Nov 3, 2022)

    Abstract

    We discuss the general features of the time-evolving reduced density matrix (RDM) of multistate systems coupled to dissipative environments and show that many important aspects of the dynamics are visualized effectively and transparently through coherence maps, defined as snapshots of the real and imaginary components of the RDM on the square grid of system sites.

    In particular, the spread, signs, and shapes of the coherence maps collectively characterize the state of the system and the nature of the dynamics, as well as the equilibrium state.

    The topology of the system is readily reflected in its coherence map.

    Rows and columns show the composition of quantum superpositions, and their filling indicates the extent of the surviving coherence.

    Linear combinations of imaginary RDM elements specify instantaneous population derivatives.

    The main diagonal comprises the incoherent component of the dynamics, while the upper/lower triangular areas give rise to coherent contributions that increase the purity of the RDM.

    In open systems, the coherence map evolves to a band surrounding the principal diagonal whose width decreases with increasing temperature and dissipation strength.

    [Article includes a list of Similar articles, with terms like: quantum process tomography, coherence signatures, tunneling dynamics, excitons and coherence, real-time path integral calculations.]

    • Arxiv > “Relation between Quantum Coherence and Quantum Entanglement in Quantum Measurements” by Ho-Joon Kim, Soojoon Lee (22 Feb 2022)

    Quantum measurement is a class of quantum channels that sends quantum states to classical states. We set up resource theories of quantum coherence and quantum entanglement for quantum measurements and find relations between them. For this, we conceive a relative entropy type quantity to account for the quantum resources of quantum measurements. The quantum coherence of a quantum measurement can be converted into the entanglement in a bipartite quantum measurement through coherence-non generating transformations. Conversely, a quantum entanglement monotone of quantum measurements induces a quantum coherence monotone of quantum measurement. Our results confirm that the understanding on the link between quantum coherence and quantum entanglement is valid even for quantum measurements which do not generate any quantum resource.

    • Wiki > Coherent state

    In physics, specifically in quantum mechanics, a coherent state is the specific quantum state of the quantum harmonic oscillator, often described as a state which has dynamics most closely resembling the oscillatory behavior of a classical harmonic oscillator.

    Quantum coherence map
    Image credit: Coherence Maps and Flow of Excitation Energy in the Bacterial Light Harvesting Complex 2

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