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Environment-assisted quantum walks in photosynthetic energy transfer

Determine the role quantum dynamical effects play in the efficiency of exciton (energy) transfer within photosynthetic molecular arrays — such as the Fenna-Matthews-Olson (FMO) protein complex, whose long-lived coherence had recently been demonstrated experimentally — that interact with a thermal bath.

quantum walkphotosynthesisenergy transferlindblad dynamicsfmo complex

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Determine the role quantum dynamical effects play in the efficiency of exciton (energy) transfer within photosynthetic molecular arrays — such as the Fenna-Matthews-Olson (FMO) protein complex, whose long-lived coherence had recently been demonstrated experimentally — that interact with a thermal bath. Mohseni, Rebentrost, Lloyd and Aspuru-Guzik develop a theoretical framework for studying the role of quantum interference effects in the energy-transfer dynamics of molecular arrays that interact with a thermal bath, working within the Lindblad formalism. To do this, they generalize continuous-time quantum walks to non-unitary and temperature-dependent dynamics in Liouville space, derived from a microscopic Hamiltonian. They explore the different physical effects of coherence and decoherence processes through a universal measure of the energy-transfer efficiency and its susceptibility. Applying the framework to the Fenna-Matthews-Olson (FMO) protein complex — for which direct evidence of long-lived coherence had recently been demonstrated experimentally, citing Engel et al., Nature 446, 782 (2007) — they demonstrate that an effective interplay between the free Hamiltonian and thermal fluctuations in the environment leads to a substantial increase in the complex's energy-transfer efficiency, from about 70% to 99%. That figure is the paper's own result about the physical efficiency of energy transfer within the FMO complex, obtained from the generalized quantum-walk framework the paper develops; it is not a claim about the running time, resource cost, or speedup of an algorithm, and the abstract states none of those for the framework itself.

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Mohseni, Rebentrost, Lloyd and Aspuru-Guzik develop a theoretical framework for studying the role of quantum interference effects in the energy-transfer dynamics of molecular arrays that interact with a thermal bath, working within the Lindblad formalism. To do this, they generalize continuous-time quantum walks to non-unitary and temperature-dependent dynamics in Liouville space, derived from a microscopic Hamiltonian. They explore the different physical effects of coherence and decoherence processes through a universal measure of the energy-transfer efficiency and its susceptibility. Applying the framework to the Fenna-Matthews-Olson (FMO) protein complex — for which direct evidence of long-lived coherence had recently been demonstrated experimentally, citing Engel et al., Nature 446, 782 (2007) — they demonstrate that an effective interplay between the free Hamiltonian and thermal fluctuations in the environment leads to a substantial increase in the complex's energy-transfer efficiency, from about 70% to 99%. That figure is the paper's own result about the physical efficiency of energy transfer within the FMO complex, obtained from the generalized quantum-walk framework the paper develops; it is not a claim about the running time, resource cost, or speedup of an algorithm, and the abstract states none of those for the framework itself. The Classiq library carries this subject under applications · chemistry. The sources read state no complexity bound for this record (The abstract of arXiv:0805.2741 states no algorithmic complexity, running time, gate count, or qubit count. Its one quantitative result is a physical efficiency figure for a specific molecular complex: "we demonstrate that for the FMO complex an effective interplay between free Hamiltonian and thermal fluctuations in the environment leads to a substantial increase in energy transfer efficiency from about 70% to 99%." That is a result about the transfer efficiency of the FMO complex itself, obtained from the paper's theoretical framework, not a bound on the cost of the generalized quantum walk or of any other algorithm; the abstract states no runtime, no query count, and no comparison of computational cost for the framework it develops. The Classiq index entry this record covers, applications/chemistry/quantum_walk_fmo, gives a directory path and a file list and states no bound. Those are the only sources read for this field, and the complexity field is left empty on purpose rather than filled with an efficiency figure that is not a complexity bound.).

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environment-assisted-quantum-walk.txt
ALGORITHM: Environment-assisted quantum walks in photosynthetic energy transfer
PROBLEM: Determine the role quantum dynamical effects play in the efficiency of exciton (energy) transfer within photosynthetic molecular arrayssuch as the Fenna-Matthews-Olson (FMO) protein complex, whose long-lived coherence had recently been demonstrated experimentallythat interact with a thermal bath.
IDEA: Mohseni, Rebentrost, Lloyd and Aspuru-Guzik develop a theoretical framework for studying the role of quantum interference effects in the energy-transfer dynamics of molecular arrays that interact with a thermal bath, working within the Lindblad formalism. To do this, they generalize continuous-time quantum walks to non-unitary and temperature-dependent dynamics in Liouville space, derived from a microscopic Hamiltonian. They explore the different physical effects of coherence and decoherence processes through a universal measure of the energy-transfer efficiency and its susceptibility. Applying the framework to the Fenna-Matthews-Olson (FMO) protein complexfor which direct evidence of long-lived coherence had recently been demonstrated experimentally, citing Engel et al., Nature 446, 782 (2007) — they demonstrate that an effective interplay between the free Hamiltonian and thermal fluctuations in the environment leads to a substantial increase in the complex's energy-transfer efficiency, from about 70% to 99%. That figure is the paper's own result about the physical efficiency of energy transfer within the FMO complex, obtained from the generalized quantum-walk framework the paper develops; it is not a claim about the running time, resource cost, or speedup of an algorithm, and the abstract states none of those for the framework itself.
REPORTED COST: Not stated by the sources read
BASIS: The abstract of arXiv:0805.2741 states no algorithmic complexity, running time, gate count, or qubit count. Its one quantitative result is a physical efficiency figure for a specific molecular complex: "we demonstrate that for the FMO complex an effective interplay between free Hamiltonian and thermal fluctuations in the environment leads to a substantial increase in energy transfer efficiency from about 70% to 99%." That is a result about the transfer efficiency of the FMO complex itself, obtained from the paper's theoretical framework, not a bound on the cost of the generalized quantum walk or of any other algorithm; the abstract states no runtime, no query count, and no comparison of computational cost for the framework it develops. The Classiq index entry this record covers, applications/chemistry/quantum_walk_fmo, gives a directory path and a file list and states no bound. Those are the only sources read for this field, and the complexity field is left empty on purpose rather than filled with an efficiency figure that is not a complexity bound.
DEMONSTRATED BY: the Classiq library entry applications/chemistry/quantum_walk_fmo
PRIMARY SOURCE: Masoud Mohseni, Patrick Rebentrost, Seth Lloyd, Alán Aspuru-Guzik (2008), Environment-Assisted Quantum Walks in Photosynthetic Energy Transferhttps://arxiv.org/abs/0805.2741

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Literature & references
Environment-Assisted Quantum Walks in Photosynthetic Energy Transfer2008 · Masoud Mohseni, Patrick Rebentrost, Seth Lloyd, Alán Aspuru-Guzik

Primary source: it develops the Lindblad-formalism theoretical framework and the generalization of continuous-time quantum walks to non-unitary, temperature-dependent Liouville-space dynamics, and reports the resulting increase in the FMO complex's energy-transfer efficiency from about 70% to 99%. Consult it for the universal efficiency-and-susceptibility measure, the microscopic Hamiltonian the dynamics are derived from, and the derivation connecting the free-Hamiltonian/thermal-fluctuation interplay to the reported efficiency figure, none of which the abstract states in detail.

arxiv.org/abs/0805.2741