Biological processes reveal abilities which are very impressive and cannot be adequately explained with the only use of traditional (classical) approaches. A certain amount of quantum mechanics is thought to be used by nature in order to enhance the efficiency of the underlying processes. The question which arises then is: How can quantum features survive in an open quantum system subject to a permanent environmental noise? In this paper we shall present a mathematical model for the illustration of the excitation energy transfer in photosynthesis complexes, with the aim to study the "constructive" interplay between the coherent quantum excitation transfer and the vibrational classical motion of the underlying molecular structure. The model is based on the Schrödinger equation associated to a time-dependent Hamiltonian, describing the propagation of an absorbed photon through a spin-chain towards the reaction center of the photosynthesis apparatus (Spin-Boson model).
Biological processes reveal abilities which are very impressive and cannot be adequately explained with the only use of traditional (classical) approaches. A certain amount of quantum mechanics is thought to be used by nature in order to enhance the efficiency of the underlying processes. The question which arises then is: How can quantum features survive in an open quantum system subject to a permanent environmental noise? In this paper we shall present a mathematical model for the illustration of the excitation energy transfer in photosynthesis complexes, with the aim to study the "constructive" interplay between the coherent quantum excitation transfer and the vibrational classical motion of the underlying molecular structure. The model is based on the Schrödinger equation associated to a time-dependent Hamiltonian, describing the propagation of an absorbed photon through a spin-chain towards the reaction center of the photosynthesis apparatus (Spin-Boson model).
Open quantum system approaches are widely used in the description of physical, chemical and biological systems. A famous example is electronic excitation transfer in the initial stage of photosynthesis, where harvested energy is transferred with remarkably high efficiency to a reaction center. This transport is affected by the motion of a structured vibrational environment, which makes simulations on a classical computer very demanding. Here we propose an analog quantum simulator of complex open system dynamics with a precisely engineered quantum environment. Our setup is based on superconducting circuits, a well established technology. As an example, we demonstrate that it is feasible to simulate exciton transport in the Fenna–Matthews–Olson photosynthetic complex. Our approach allows for a controllable single-molecule simulation and the investigation of energy transfer pathways as well as non-Markovian noise-correlation effects.
In natural photosynthesis systems, pigment-protein complexes harvest the photon from sunlight with near-unity quantum efficiency. These complexes show incredible properties that cannot be merely extrapolated from knowledge of their composition. Additionally, the environment perturbing the light-harvesting process significantly affects the mechanism of photosynthesis. This research investigates the photosystem II reaction center (PSII RC) from a new perspective which considers the restricted path of the exciton transfer, in the photosynthesis system, as a quantum trajectory picture with the quantum continuous measurement. In this work, the corridor path of exciton transfer dynamics satisfies the equation of motion, as the spin dynamics, which consists of precession, relaxation, and random force rapidly fluctuating spin splitting arising from the bath. Moreover, the width of the corridor is an important factor for restricting path dynamics resulting in the localization and decoherence phenomenon. Our method is to analyze exciton transfer dynamics through paths on the Bloch sphere, in order to investigate the propagating states in accordance with the weight functional which depends on the coupling parameter between the system and environment as the phonon bath. Our results show that the paths outside the width of the corridor have a considerably lower weight functional and decoherence functional than those inside the width. Therefore, the degrees of localization, the weight functional, and the decoherence functional are related. Furthermore, the simulation reveals three characteristics of exciton transfer: gradual transfer, no transfer, and rapid transfer, relying significantly on the coupling between the system and phonons.
Abstract Amplification of quantum transfer and ratchet–type processes are important for quantum technologies. We also expect that quantum ratchet works in quantum photosynthesis, where possible role of quantum effects is now widely discussed but the underlying dynamical processes are still not clearly known. In this work, we study a model of amplification of quantum transfer and making it directed, which we call the quantum ratchet model. The model is based on a special quantum control master equation with dynamics induced by a feedback-type process. The ratchet effect is achieved in the quantum control model with dissipation and sink, where the Hamiltonian depends on vibrations in the energy difference synchronized with transitions between energy levels. A similarity between this model and the model of coherent transport in quantum photosynthesis, where the time dependence of the Hamiltonian arises due to vibrons, is studied. Amplitude and frequency of the oscillating vibron together with the dephasing rate are the parameters of the quantum ratchet which determine its efficiency. We study with which parameters the quantum ratchet minimizes the exction recombination time and show that the experimentally known values of the parameters of the photosynthetic reaction center correspond to values of the parameters of the quantum ratchet which realize a local minimum of the exciton recombination time. We also find other values of the parameters of the quantum ratchet minimizing the exciton recombination time, which correspond to a twice smaller frequency of the vibron compared to that observed in experiments.
In this paper, we present a theoretical description to the quantum coherence and decoherence phenomena of energy transfer in photosynthesis observed in a recent experiment [see Science 316, 1462 (2007)]. As a successive two-color laser pulses with selected frequencies cast on a sample of the photosynthetic purple bacterium Rb. sphaeroides two resonant excitations of electrons in chromophores can be generated. However, this effective two-level subsystem will interact with its protein environment and decoherence is inevitable. We describe this subsystem coupled with its environment as a dynamical spin-boson model. The non-Markovian decoherence dynamics is described using a quasi-adiabatic propagator path integral (QUAPI) approach. With the photon-induced effective time-dependent level splitting energy and level flip coupling coefficient between the two excited states and the environment-induced non-Markovian decoherence dynamics, our theoretical result is in good agreement with the experimental data.
Understanding how quantum coherence is regulated by structured environments is essential for elucidating energy-transfer mechanisms in photosynthetic light-harvesting complexes. In this work, we present a trajectory-based computational analysis of the quantum-classical transition in asymmetrically coupled spin-boson models, motivated by exciton-phonon interactions in the phycobiliprotein PC645 complex. The model captures site-dependent environmental coupling that mimics pigment-specific dissipation pathways in biological systems. We employ three complementary approaches: a Redfield master equation in the Bloch-vector representation, numerically exact hierarchical equations of motion (HEOM), and a stochastic Schrödinger equation that generates ensembles of quantum trajectories. Within the stochastic framework, environmental backaction is interpreted as a continuous measurement process, giving rise to a time-dependent dynamical corridor on the Bloch sphere. The corridor width provides a quantitative measure of coherence loss and defines the quantum-classical crossover time. Our results show that moderate asymmetric coupling can sustain coherence and enhance directional population transfer, whereas strong coupling rapidly suppresses quantum trajectories. These findings offer mechanistic insight into environmentally assisted energy transfer and coherence regulation in photosynthetic pigment-protein complexes.
Many living organisms can exploit quantum mechanical effects to gain distinct biological advantages. In plants, photosynthesis uses quantum coherence to achieve near 100% efficiency in energy transfer. With advances in experimental techniques, two-dimensional electronic spectroscopy can reveal dynamic processes such as coherence and coupling within a system, and it plays an important role in studying energy transfer in photosynthesis. On the theory side, methods such as the generalized Bloch-Redfield theory and the hierarchical equations of motion are used to model photosynthetic systems. Quantum simulation, as a high-efficiency and low-complexity approach, has also made progress across various platforms in the study of photosynthesis. In recent years, a series of studies has introduced quantum coherence into artificial systems to enhance energy transfer efficiency, laying the groundwork for the design of coherent devices with efficient energy transport. Birds can use the weak geomagnetic field and spin-dependent chemical reactions to detect direction. Theoretical frameworks for animal navigation include magnetite-based mechanisms, magnetoreceptor genes, and the radical-pair mechanism. Quantum simulations of navigation have also advanced on multiple platforms. Inspired by animal navigation, diverse quantum effects have been applied to improve sensing and to support navigation tasks. This paper presents a comprehensive review of progress on quantum coherence in photosynthesis and avian navigation, along with related theoretical methods, quantum simulation approaches, and research on quantum coherent devices.