Abstract In a network of interacting quantum systems, achieving fast coherent energy transfer is a challenging task. While quantum systems are susceptible to a wide range of environmental factors, in many physical settings their interactions with quantized vibrations, or phonons, of a supporting structure are the most prevalent. This leads to noise and decoherence in the network, ultimately impacting the energy-transfer process. In this work, we introduce a novel type of coherent energy-transfer mechanism for quantum systems, where phonon interactions are able to actually enhance the energy transfer. Here, a shared phonon interacts with the systems and dynamically adjusts their resonances, providing remarkable directionality combined with quantum speed-up. We call this mechanism phonon-induced dynamic resonance energy transfer and show that it enables long-range coherent energy transport even in highly disordered systems.
Abstract In a network of interacting quantum systems, achieving fast coherent energy transfer is a challenging task. While quantum systems are susceptible to a wide range of environmental factors, in many physical settings their interactions with quantized vibrations, or phonons, of a supporting structure are the most prevalent. This leads to noise and decoherence in the network, ultimately impacting the energy-transfer process. In this work, we introduce a novel type of coherent energy-transfer mechanism for quantum systems, where phonon interactions are able to actually enhance the energy transfer. Here, a shared phonon interacts with the systems and dynamically adjusts their resonances, providing remarkable directionality combined with quantum speed-up. We call this mechanism phonon-induced dynamic resonance energy transfer and show that it enables long-range coherent energy transport even in highly disordered systems.
In a network of interacting quantum systems, achieving fast coherent energy transfer is a challenging task. While quantum systems are susceptible to a wide range of environmental factors, in many physical settings their interactions with quantized vibrations, or phonons, of a supporting structure are the most prevalent. This leads to noise and decoherence in the network, ultimately impacting the energy-transfer process. In this work, we introduce a novel type of coherent energy-transfer mechanism for quantum systems, where phonon interactions are able to actually enhance the energy transfer. Here, a shared phonon interacts with the systems and dynamically adjusts their resonances, providing remarkable directionality combined with quantum speed-up. We call this mechanism phonon-induced dynamic resonance energy transfer and show that it enables long-range coherent energy transport even in highly disordered systems.
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.
Quantum properties like coherence and entanglement can lead to enhanced performance characteristics in a wide range of applications including quantum computation, quantum memory storage, optical sensing, and energy harvesting. Entanglement is very sensitive to static and dynamical disorder. Similarly, the generation of highly-entangled states requires strong coupling or strong driving fields. Satisfying all of these requirements is generally quite difficult. In the first part of this thesis, we present an approach to overcome these limitations through the use of exotic light-matter states in hyperbolic media which provide a new approach to control quantum correlations and interatomic interactions. We reveal a class of excited-state, long-range interactions, referred to as Super-Coulombic interactions that are singular along a material-dependent resonance angle. In practical systems, the Super-Coulombic interaction achieves dipole-dipole coupling that is orders of magnitude larger than conventional approaches, while also occurring across a large frequency bandwidth making it robust to static energy-level disorder. This unique hyperbolic response is not only naturally occurring, found in materials like h-BN, BiTe2, BiSe2, and mono-layered black phosphorus, but can also be designed with artificial nanostructured materials (metamaterials) to create the desired hyperbolic dispersion across different parts of the electromagnetic spectrum. Our theoretical prediction motivated an intense search for the effect and was confirmed by an experimental demonstration at room temperature. To obtain agreement with experimental results, we present a rigorous theoretical framework that takes into account ensemble effects, finite-sized effects, and dimensional effects that arise from confined geometries ultimately modifying the Super-Coulombic spatial scaling law. In the second part of this thesis, we solve an outstanding theoretical problem dealing with the control of resonance energy transfer in nanophotonic environments in both the incoherent and coherent coupling limits. Resonance energy transfer is a fundamental process that is the subject of intense research across all sciences. For example, in chemistry for drug delivery and chemical monitoring, in engineering for photovoltatic and up-conversion devices, and in biology for exciton transport within photosynthetic complexes. First, we consider the disordered and weak coupling limit of resonance energy transfer often encountered in chemistry. We propose new design principles for enhancing and suppressing the energy transfer rate and efficiency quantitatively captured by a simple image dipole model. Our theory explains a wide range of experimental results which have been the subject of an ongoing debate for the past 15 years. Second, we present our recent result aimed at understanding the fundamental role of entanglement and quantum coherence in resonance energy transfer. To uncover the role of these effects, we develop a unified theory of energy transfer valid from the incoherent to quantum coherent coupling regimes. Ultimately, our theory reveals a fundamental bound ηmax = γa for energy transfer efficiency arising from γd+γa the spontaneous emission rates γd and γa of the donor and acceptor. This bound provides an upper limit to the efficiency of energy transfer regardless of quantum coherence or entanglement, suggesting new design principles for achieving near-unity energy transfer efficiency in coherent systems. The result has important implications for the two-chromophore model found in photosynthetic complexes and paves the way for nanophotonic analogues of efficiency-enhancing environments mimicking biological photosynthetic systems.
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.
Particle or energy transfer through quantum networks is determined by network topology and couplings to environments. This study examines the combined effect of topology and external couplings on the efficiency of directional quantum transfer through quantum networks. We consider a microscopic model of qubit networks coupled to external vibrations by Holstein and Peierls couplings. By treating the positions of the network sites and the site-dependent phonon frequencies as independent variables, we determine the Hamiltonian parameters corresponding to minimum transfer time by Bayesian optimization. The results show that Holstein couplings may accelerate transfer through suboptimal network configurations but cannot accelerate quantum dynamics beyond the limit of the transfer time in an optimal phonon-free configuration. By contrast, Peierls couplings distort the optimal networks to accelerate quantum transfer through configurations with less than six sites. However, the speed-up offered by Peierls couplings decreases with the network size and disappears for networks with more than seven sites. For networks with seven sites or more, Peierls couplings distort the optimal network configurations and change the mechanism of quantum transfer but do not affect the lower limit of the transfer time. The machine-learning approach demonstrated here can be applied to determine quantum speed limits in other applications.
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 behaviours: 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 neighbour 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.