Abstract Quantum coherence is increasingly recognized as a foundational resource in quantum thermodynamics, serving as a key driver of thermodynamic performance in quantum heat engines (QHEs). However, a central paradox remains unresolved: how do natural photosynthetic systems achieve exceptionally high and robust energy-conversion efficiencies, even within noisy, dissipative environments where quantum coherence typically decays rapidly? Here, we present a coherently driven four-level QHE model, inspired by photosystem II—the primary energy-harvesting complex in plants, to elucidate the mechanisms by which quantum coherence and system topology jointly enable extraordinary efficiency and resilience. By performing spectral analysis of the system’s non-Hermitian Liouvillian superoperator, we reveal a topological phase transition characterized by a quantized change in the winding number. This transition separates two operational regimes: in the topologically trivial phase, stronger driving enhances coherence and boosts efficiency, whereas in the topologically nontrivial phase, topological protection preserves optimal efficiency even as coherence is largely destroyed. Our results establish a direct connection between topological effects and photosynthetic energy conversion, providing a new framework for understanding the resilience of biological energy harvesting and informing the design of robust, high-efficiency quantum energy conversion devices.
Abstract Quantum coherence is increasingly recognized as a foundational resource in quantum thermodynamics, serving as a key driver of thermodynamic performance in quantum heat engines (QHEs). However, a central paradox remains unresolved: how do natural photosynthetic systems achieve exceptionally high and robust energy-conversion efficiencies, even within noisy, dissipative environments where quantum coherence typically decays rapidly? Here, we present a coherently driven four-level QHE model, inspired by photosystem II—the primary energy-harvesting complex in plants, to elucidate the mechanisms by which quantum coherence and system topology jointly enable extraordinary efficiency and resilience. By performing spectral analysis of the system’s non-Hermitian Liouvillian superoperator, we reveal a topological phase transition characterized by a quantized change in the winding number. This transition separates two operational regimes: in the topologically trivial phase, stronger driving enhances coherence and boosts efficiency, whereas in the topologically nontrivial phase, topological protection preserves optimal efficiency even as coherence is largely destroyed. Our results establish a direct connection between topological effects and photosynthetic energy conversion, providing a new framework for understanding the resilience of biological energy harvesting and informing the design of robust, high-efficiency quantum energy conversion devices.
The lifetime of a quantum state, denoted τ, is a fundamental characteristic determining the coherence time and operational reliability of quantum technologies. Conventional approaches to extend τ rely on dynamical decoupling, material purification, or engineered dissipation, yet these methods generally scale poorly with system size and are vulnerable to environmental noise. This paper introduces a novel theoretical framework whereby τ is determined by a topological invariant T of the underlying quantum system: τ = f(T). By establishing a rigorous connection between the spectrum of the Liouvillian superoperator, the topology of the system's Hilbert space, and the decay dynamics of density matrices, we demonstrate that certain topologically nontrivial phases inherently suppress relaxation channels and thus guarantee a finite lower bound on τ. We present a detailed derivation for a class of spin chains with nearest‑neighbor interactions and illustrate how the winding number of the Bloch Hamiltonian controls the lifetime of edge states. The formalism is generalized to higher‑dimensional lattice models and to systems with non‑Hermitian Hamiltonians. We discuss implications for fault‑tolerant quantum computation, robust quantum memories, and the design of synthetic quantum matter with engineered lifetimes. This work lays the foundation for a new branch of quantum stability theory that harnesses topological protection not only of energy levels but of dynamical lifetimes, potentially opening pathways toward scalable, intrinsically protected quantum devices.
Abstract Near-unity energy transfer efficiency has been widely observed in natural photosynthetic complexes. This phenomenon has attracted broad interest from different fields, such as physics, biology, chemistry, and material science, as it may offer valuable insights into efficient solar-energy harvesting. Recently, quantum coherent effects have been discovered in photosynthetic light harvesting, and their potential role on energy transfer has seen the heated debate. Here, we perform an experimental quantum simulation of photosynthetic energy transfer using nuclear magnetic resonance (NMR). We show that an N-chromophore photosynthetic complex, with arbitrary structure and bath spectral density, can be effectively simulated by a system with log2N qubits. The computational cost of simulating such a system with a theoretical tool, like the hierarchical equation of motion, which is exponential in N, can be potentially reduced to requiring a just polynomial number of qubits N using NMR quantum simulation. The benefits of performing such quantum simulation in NMR are even greater when the spectral density is complex, as in natural photosynthetic complexes. These findings may shed light on quantum coherence in energy transfer and help to provide design principles for efficient artificial light harvesting.
Quantum coherence is a useful resource for increasing the speed and decreasing the irreversibility of quantum dynamics. Because of this feature, coherence is used to enhance the performance of various quantum information processing devices beyond the limitations set by classical mechanics. However, when we consider thermodynamic processes, such as energy conversion in nanoscale devices, it is still unclear whether coherence provides similar advantages. Here we establish a universal framework, clarifying how coherence affects the speed and irreversibility in thermodynamic processes described by the Lindblad master equation, and give general rules for when coherence enhances or reduces the performance of thermodynamic devices. Our results show that a proper use of coherence enhances the heat current without increasing dissipation; i.e., coherence can reduce friction. In particular, if the amount of coherence is large enough, this friction becomes virtually zero, realizing a superconducting-like "dissipation-less" heat current. Since our framework clarifies a general relation among coherence, energy flow, and dissipation, it can be applied to many branches of science from quantum information theory to biology. As an application to energy science, we construct a quantum heat engine cycle that exceeds the power-efficiency trade-off bound on classical engines and effectively attains the Carnot efficiency with finite power in fast cycles.
Finite-time quantum heat engines (QHEs) typically extract less work than their quasistatic counterparts because fast driving generates coherences and non-adiabatic transitions during the work strokes, a phenomenon commonly referred to as quantum friction. Quantum lubrication denotes a broad class of strategies that use auxiliary systems or controls to mitigate this loss. In this work, we introduce a lubrication protocol based on the quantum Zeno dynamics (QZD). By coupling the working medium to an auxiliary lubricant system and frequently monitoring the lubricant, we confine the joint evolution to a Zeno subspace and obtain an effective shortcut to adiabaticity during the work strokes of a QHE running an Otto cycle. In the ideal Zeno limit, the protocol reproduces the transitionless dynamics required to preserve populations in the instantaneous energy basis and recover the Otto efficiency at finite stroke duration. We also analyze several implementation-dependent thermodynamic costs, including switching, driving, monitoring, and imperfect thermalization, in order to assess how these costs constrain the practical gains in efficiency and power. Our results identify QZD as a conceptually distinct route to quantum lubrication and highlight quantum heat engines as a useful setting in which to study the interplay between strong coupling, measurement, and quantum thermodynamic control.
We consider a recently proposed four-level quantum heat engine (QHE) model to analyze the role of quantum coherences in determining the thermodynamic properties of the engine, such as flux, output power, and efficiency. A quantitative analysis of the relative effects of the coherences induced by the two thermal baths is brought out. By taking account of the dissipation in the cavity mode, we define useful work obtained from the QHE and present some analytical results for the optimal values of relative coherences that maximizes flux (hence output power) through the engine. We also analyze the role of quantum effects in inducing population inversion (lasing) between the states coupled to the cavity mode. The universal behavior of the efficiency at maximum power (EMP) is examined. In accordance with earlier theoretical predictions, to leading order, we find that $\mathrm{EMP}\ensuremath{\sim}{\ensuremath{\eta}}_{c}/2$, where ${\ensuremath{\eta}}_{c}$ is Carnot efficiency. However, the next higher order coefficient is system dependent and hence nonuniversal.
Traditional thermodynamics, built upon the foundation of Hermitian quantum mechanics, primarily describes closed or weakly open systems where energy is conserved. However, the ubiquitous presence of dissipation and gain in realistic physical and biological systems necessitates a more generalized framework. Non-Hermitian quantum mechanics, characterized by Hamiltonians with complex eigenvalues, naturally accounts for such open systems and their interaction with the environment. This paper explores the burgeoning field of non-Hermitian thermodynamics, which aims to extend classical and quantum thermodynamic principles to systems exhibiting energy exchange with their surroundings. We delve into how non-Hermiticity provides a natural language for describing processes involving dissipation, gain, and decoherence, thereby offering a unified perspective on these phenomena. Key concepts such as PT-symmetry, exceptional points, and generalized definitions of work, heat, and entropy in non-Hermitian settings are reviewed. The paper discusses the implications for fundamental thermodynamic laws, the performance of non-Hermitian heat engines, and the role of coherence in energy transport. By embracing the mathematical elegance and physical insights of non-Hermitian physics, we propose a comprehensive framework that unifies the seemingly disparate concepts of dissipation and coherence within a consistent thermodynamic theory, paving the way for advanced applications in quantum technologies, materials science, and biological energy transfer.