Abstract Nontrivial quantum effects in biological systems are of high interest among physicists over the past decade. They allow for information and energy to be exchanged with near-unity efficiency despite hindered by the warm, wet, and noisy environment. Several models suggests that the efficient quantum energy transport is due to the interplay between dephasing dynamics and unitary evolution of the disordered biological systems i.e in photosynthetic complex. However, the proposed models have not yet included the driving force depicting the external perturbation used in the experiment such as laser in 2D spectroscopy involved in the detection of the exciton transfer or an artificial quantum transport experiments. Here, we resolve this issue by subjecting the dephasing assisted transport model by Plenio and Huelga [New J. Phys. 10, 11 (2012)] to a driving force. We analyze dynamical evolution of the driven system and show that further efficiency enhancement achieved by driving the transport site. We also discuss some experimental realizations of the quantum transport system.
Abstract Nontrivial quantum effects in biological systems are of high interest among physicists over the past decade. They allow for information and energy to be exchanged with near-unity efficiency despite hindered by the warm, wet, and noisy environment. Several models suggests that the efficient quantum energy transport is due to the interplay between dephasing dynamics and unitary evolution of the disordered biological systems i.e in photosynthetic complex. However, the proposed models have not yet included the driving force depicting the external perturbation used in the experiment such as laser in 2D spectroscopy involved in the detection of the exciton transfer or an artificial quantum transport experiments. Here, we resolve this issue by subjecting the dephasing assisted transport model by Plenio and Huelga [New J. Phys. 10, 11 (2012)] to a driving force. We analyze dynamical evolution of the driven system and show that further efficiency enhancement achieved by driving the transport site. We also discuss some experimental realizations of the quantum transport system.
For many years, the fields of quantum optics and biology have rarely shared a common path. In quantum optics, most of the concepts and techniques developed over the years stand for systems where only a few degrees of freedom are considered and, more importantly, where the systems under study are assumed to be completely isolated from their surrounding environment. This situation is far from what we can find in nature. Biological complexes are, by definition, warm, wet and noisy systems subjected to environmental fluctuations, where quantum phenomena are unlikely to be observed. Notwithstanding, in recent years, this paradigm has begun to be questioned by several works where quantum-mechanical concepts have been introduced in order to describe the dynamics of important biological processes, such as energy transport in photosynthetic light-harvesting complexes. The goal of this thesis is twofold. Firstly, we will investigate how ideas and techniques routinely used in quantum optics can be exploited in order to develop new quantum-based spectroscopy techniques and, secondly, we will examine to what extent microscopic quantum phenomena could impact on the efficient transport behavior of photosynthetic light-havesting complexes. This problem is particularly relevant, because the understanding of the fundamental mechanisms that enable the highly efficient transport of energy in photosynthetic systems could lead us to the design of future quantum-inspired light-harvesting technologies, such as high-efficiency organic solar cells.
Transport phenomena are fundamental in physics. They allow for information and energy to be exchanged between individual constituents of communication systems, networks or even biological entities. Environmental noise will generally hinder the efficiency of the transport process. However, and contrary to intuition, there are situations in classical systems where thermal fluctuations are actually instrumental in assisting transport phenomena. Here we show that, even at zero temperature, transport of excitations across dissipative quantum networks can be enhanced by local dephasing noise. We explain the underlying physical mechanisms behind this phenomenon and propose possible experimental demonstrations in quantum optics. Our results suggest that the presence of entanglement does not play an essential role for energy transport and may even hinder it. We argue that Nature may be routinely exploiting dephasing noise and show that the transport of excitations in simplified models of light harvesting molecules does benefit from such noise assisted processes. These results point toward the possibility for designing optimized structures for transport, for example in artificial nanostructures, assisted by noise.
Abstract Quantum effects in photosynthetic energy transport in nature, especially for the typical Fenna-Matthews-Olson (FMO) complexes, are extensively studied in quantum biology. Such energy transport processes can be investigated as open quantum systems that blend the quantum coherence and environmental noise, and have been experimentally simulated on a few quantum devices. However, the existing experiments always lack a solid quantum simulation for the FMO energy transport due to their constraints to map a variety of issues in actual FMO complexes that have rich biological meanings. Here we successfully map the full coupling profile of the seven-site FMO structure by comprehensive characterisation and precise control of the evanescent coupling of the three-dimensional waveguide array. By applying a stochastic dynamical modulation on each waveguide, we introduce the base site energy and the dephasing term in coloured noise to faithfully simulate the power spectral density of the FMO complexes. We show our photonic model well interprets the phenomena including reorganisation energy, vibrational assistance, exciton transfer and energy localisation. We further experimentally demonstrate the existence of an optimal transport efficiency at certain dephasing strength, providing a window to closely investigate environment-assisted quantum transport.
The transport of excitations governs fundamental properties of matter. Particularly rich physics emerges in the interplay between disorder and environmental noise, even in small systems such as photosynthetic biomolecules. Counterintuitively, noise can enhance coherent quantum transport, which has been proposed as a mechanism behind the high transport efficiencies observed in photosynthetic complexes. This effect has been called ``environment-assisted quantum transport''. Here, we propose a quantum simulation of the excitation transport in an open quantum network, taking advantage of the high controllability of current trapped-ion experiments. Our scheme allows for the controlled study of various different aspects of the excitation transfer, ranging from the influence of static disorder and interaction range, over the effect of Markovian and non-Markovian dephasing, to the impact of a continuous insertion of excitations. Our paper discusses experimental error sources and realistic parameters, showing that it can be implemented in state-of-the-art ion-chain experiments.
Abstract Simulating charge and energy transfer in extended molecular networks requires an effective model to include the environment because it significantly affects the quantum dynamics. A prototypical effect known as environment-assisted quantum transport (ENAQT) consists in the enhancement of the transfer efficiency by the interaction with an environment. A simple description of this phenomenon is obtained by a quantum master equation describing a quantum walk over the molecular network in the presence of inter-site decoherence. We consider the problem of simulating the dynamics underlying ENAQT in a digital quantum computer. Two different quantum algorithms are introduced, the first one based on stochastic Hamiltonians and the second one based on a collision scheme. We test both algorithms by simulating ENAQT in a small molecular network on a quantum computer emulator and provide a comparative analysis of the two approaches. Both algorithms can be implemented in a memory efficient encoding with the number of required qubits scaling logarithmically with the size of the simulated system while the number of gates increases quadratically. We discuss the algorithmic quantum trajectories generated by the two simulation strategies showing that they realize distinct unravellings of the site-dephasing master equation. In our approach, the non-unitary dynamics of the open system is obtained through effective representations of the environment, paving the way to digital quantum simulations of quantum transport influenced by structured environments.
Abstract Transport phenomena are ubiquitous throughout the science, engineering, and technology disciplines as it concerns energy, mass, charge, and information exchange between systems. In particular, energy transport in the nanoscale regime has attracted significant attention within the physical science community due to its potential to explain complex phenomena like the electronic energy transfer in molecular crystals or the Fenna-Matthews-Olson (FMO)/light harvesting complexes in photosynthetic bacteria with long time coherences. Energy transport in these systems is highly affected by environmental noise but surprisingly not always in a detrimental way. It was recently found that situations exist where noise actually enhances the transport phenomena. Such noise can take many forms, but can be characterised in three basic behaviors: quantum, correlation in time, or space. All have been shown potential to offer an energy transport enhancement. The focus of this work is on quantum transport caused by stochastic environment with spatio-temporal correlation. We consider a multi-site nearest neighbor interaction model with pure dephasing environmental noise with spatio-temporal correlation and show how an accelerated rate for the energy transfer results especially under negative spatial correlation (anti-correlation). Spatial anti-correlation provides another control parameter to help one establish the most efficient transfer of energy and may provide new insights into the working of exciton transport in photosynthetic complexes. Further the usage of spatio-temporal correlated noise may be a beneficial resource for efficient transport in large scale quantum networks.