When the revolutionary conceptual structure for the description of the physical world which we know as quantum mechanics was first formulated nearly 90 years ago, and its predictions tested in the laboratory, most of the experiments in question were on systems which were both very well characterized and reasonably well isolated from their environments, such as single electrons and atoms, small molecules and near-perfect crystalline solids. While from the very start most physicists have taken it for granted that the formalism of quantum mechanics, when combined with appropriate system-specific information, can “in principle” account for all phenomena occurring in the physical world, including those usually regarded as the subject-matter of biology, until quite recently the overwhelmingly majority opinion has been that in a biological context the role of quantum theory is confined to elucidating the equilibrium structures of the relevant molecules and their reaction processes, and that subtle phenomena such as superposition and entanglement, of which we can now routinely exhibit spectacular effects at the level of a few well-isolated photons or atoms, play at most a very indirect role in any phenomena of biological interest. A major reason conventionally given for this view has been that biological systems, at least working ones, are by their very nature “warm and wet” – a phrase which in the physicist's lexicon translates to “prone to massive decoherence”; it looks as though any interesting superposition, say of different energy eigenstates of one's system, would be rapidly decohered by the ever-present, and usually microscopically very complex, environment.
When the revolutionary conceptual structure for the description of the physical world which we know as quantum mechanics was first formulated nearly 90 years ago, and its predictions tested in the laboratory, most of the experiments in question were on systems which were both very well characterized and reasonably well isolated from their environments, such as single electrons and atoms, small molecules and near-perfect crystalline solids. While from the very start most physicists have taken it for granted that the formalism of quantum mechanics, when combined with appropriate system-specific information, can “in principle” account for all phenomena occurring in the physical world, including those usually regarded as the subject-matter of biology, until quite recently the overwhelmingly majority opinion has been that in a biological context the role of quantum theory is confined to elucidating the equilibrium structures of the relevant molecules and their reaction processes, and that subtle phenomena such as superposition and entanglement, of which we can now routinely exhibit spectacular effects at the level of a few well-isolated photons or atoms, play at most a very indirect role in any phenomena of biological interest. A major reason conventionally given for this view has been that biological systems, at least working ones, are by their very nature “warm and wet” – a phrase which in the physicist's lexicon translates to “prone to massive decoherence”; it looks as though any interesting superposition, say of different energy eigenstates of one's system, would be rapidly decohered by the ever-present, and usually microscopically very complex, environment.
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.
Many quantum predictions seem to defy “common sense” and appear beyond the comprehension of some of the greatest human minds. Richard Feynman states that “ I think I can safely say that nobody understands quantum mechanics ” in his book entitled The Character of Physical Laws . 1 Many pioneers of quantum theories have constructed examples to highlight this situation. These examples are now known as quantum paradoxes . Moreover, the common understanding that only microscopic systems behave quantum mechanically is incorrect. Macroscopic systems, e.g., superconducting systems and Bose-Einstein condensate, also exhibit quantum behaviour. These systems do not satisfy the properties of orthodox quantum systems. 2
Introduction Key features of quantum mechanics are the uncertainty principle, wave–particle duality, quantization of energies and the modification of classical probability laws. Biology is concerned with how natural systems function – from understanding how genetically coded information is replicated, to attaining a mechanistic model for complex multistep reactions. Recently researchers have been asking whether quantum mechanics, normally the domain of physics, is also needed to understand some biological processes. This field includes fascinating developments in theory and experiment, as well as multidisciplinary discussion, and the state-of-the-art is documented in this book. Erwin Schrödinger, in his famous book What is Life ? (Schrödinger, 1944), noted that quantum mechanics accounts for the stability of living things and their cellular processes because of our understanding, via quantum mechanics, of the stability and structure of molecules. The fact that quantum effects create, sometimes large, energy gaps between different states of a chemical system is also important. Such energy gaps, between electronic energy levels, enable living organisms to capture and store the energy carried from the sun by photons, and to visualize the world around them via optically induced chemical reactions. Davydov's view in Biology and Quantum Mechanics (Davydov, 1982) was that quantum mechanics is most relevant for isolated systems in pure states and therefore is of little importance for biological systems that are in statistical states at thermal equilibrium.
Quantum mechanics is our most successful physical theory. It underlies our very detailed understanding of atomic physics, chemistry, and nuclear physics, and the many technologies to which physical systems in these regimes give rise. Additionally, relativistic quantum mechanics is the basis for the standard model of elementary particles, which very successfully gives a partial unification of the forces operating at the atomic, nuclear, and subnuclear levels. However, from its inception the probabilistic nature of quantum mechanics, and the fact that “quantum measurements” in the orthodox formulation appear to require the intervention of non-quantum mechanical “classical systems,” have led to speculations by many physicists, mathematicians, and philosophers of science that quantum mechanics may be incomplete. Among the Founding Fathers of quantum theory, Einstein and Schrödinger were both of the opinion that quantum mechanics is in some way unsatisfactory, and this view has been amplified in more recent profound work of John Bell, among others. In an opposing camp, many others in the physics, mathematics, and philosophy communities have attempted to provide an interpretational foundation in which quantum mechanics remains a complete and self-contained system. Among the Founding Fathers, Bohr, Born, and Heisenberg maintained that quantum mechanics is a complete system, and a number of recent proposals have been made to improve upon or to provide alternatives to their “Copenhagen Interpretation.” The debate continues, and has spawned an enormous literature.
∙ Quanta Magazine analyzes the principles of macroscopic world formation through quantum decoherence and quantum Darwinism. ∙ 'Einselection' fixes specific quantum states… similar to how life preserves information. ∙ Integrating quantum biology from physical and philosophical perspectives, redefining the fundamental principles of life's information processing. [Quantum Biology Society] An in-depth analysis has been proposed on how the bizarre phenomena of quantum mechanics transform into the solid macroscopic reality we observe, and what connection this process has with the evolution of life. Recently, the science media outlet Quanta Magazine reported through a contribution by renowned science writer Philip Ball that the theories of 'Quantum Darwinism' and 'Decoherence,' pioneered by physicist Wojciech Zurek, are the key to connecting biological systems with the macroscopic world. ■ The Reality of 'Survival of the Fittest' Created by 'Einselection' In the quantum realm, particles can exist in multiple states simultaneously (superposition), but in the macroscopic world we observe, they appear in only one definite state. According to Dr. Zurek's theory, this happens because quantum systems continuously interact with their surrounding environment, undergoing a process of 'decoherence' where information is dissipated. The core of this process is 'Einselection' (Environment-Induced Superselection). The environment does not accommodate all states; instead, it selects only the most stable and predictable states, known as 'pointer states,' and replicates them innumerably within the environment. Just as only the genetic information advantageous for survival is passed on and spreads in natural selection, the essence of 'Quantum Darwinism' is that quantum information also undergoes a 'survival of the fittest' process dictated by the environment. This ultimately forms an objective macroscopic reality that all of us can commonly perceive. ■ Life, a Product of Evolution that Anchors Quantum Information into Reality Philip Ball noted that these physical principles are strikingly similar to the way biological systems process information. He explains that the vital activities of living organisms—such as recognizing external stimuli, preserving genetic information, and controlling complex metabolic processes—are fundamentally the very processes of filtering meaningful information from quantum superpositions and anchoring them into the physical states of the real world. This report suggests that quantum biology is not merely a discipline that investigates microscopic reactions within cells. Rather, it is a grand unified theory explaining how life has utilized the universe's fundamental principles to process information and evolve. Built upon the theories of Dr. Zurek, a master of modern physics, this analysis presents a new philosophical and physical paradigm that views life as a cosmic entity where matter, information, and quantum mechanics are perfectly integrated.