Quantum biology
Quantum physics is the most fundamental set of rules underlying all biological phenomena. At the heart of every cell replication and every organism powered by the sun, particles are bound by characteristic signatures of quantum behavior, such as superposition, entanglement, tunneling, and particle and field quantization. Rarely, however, is invoking quantum theories required to explain biological phenomena–emergent laws of classical electrostatics and mechanics, statistical mechanics, networks, and natural selection often suffice. Even in fields where quantum theories are often used, such as drug design where predictions of a drug’s impact on a protein’s functionality are aided by quantum chemistry models, quantum effects are often just quantitative corrections that do not drastically affect qualitative conclusions. We seek to determine experimentally-testable criteria for quantum behavior to manifest in biological phenomena, to identify biological phenomena that can only be explained with quantum theories, and to engineer biological systems by leveraging quantum effects.
The field of quantum biology has been explored to some extent–in fact, one of quantum physics’s founding fathers, Erwin Schrodinger, dedicated much of his later research career to studying these questions–but its current growth is especially relevant in light of the recent explosion in experimental and theoretical capabilities in quantum physics, as evidenced by Google’s recent demonstration of quantum supremacy in computing, global successes in transporting qubits across many kilometers, and ever-increasing particle-by-particle control of materials, molecules, and light. Experimental quantum physicists are better equipped to rigorously test theoretical predictions than ever before.
Quantum phenomena are said to be difficult to observe in biological systems because biological systems 1) exist at temperatures that limit coherence times and 2) are disordered, naively leading to the supersedence of more emergent laws. And in fact, there have been few, if any, observations of quantum biology that “imply quantum effects are observable in macroscopic organisms, or that are crucial for the existence of life”. Neither of these characteristics, however, necessarily precludes the manifestation of quantum phenomena. At room temperature, monolayers of hexagonal boron nitride can emit single photons, and phosphorus defects in isotope-enriched diamond exhibit millisecond-long coherence times; disordered systems can manifest predictably ordered properties, such as the spatial localization of particles in a highly disordered medium. While these experimental demonstrations of quantum phenomena occurred under highly engineered conditions–such as using metamaterials, vacuum, or photons rather than electrons and nuclei in earth-like conditions–definitively assuming such phenomena cannot also manifest in biological systems would be underestimating the creative ingenuity of nature and overestimating our own. Indeed, there are many biological phenomena that are suspected of having quantum origins, such as magnetoreception, light-to-chemical energy conversion in photosynthesis, tunneling in enzymes, the vibrational theory of smell, and UV degradation of DNA via electronic excited states.
As a first step in developing the field of quantum biology, we ask whether the following quantum phenomena can manifest in biological systems and suggest specific experimental systems to study in the near-term while in parallel conceiving of ways to enhance or manifest these effects if we do find not that they already exist.
Strong light-matter coupling in enzymes Enzymes are proteins in cells that control the rate of chemical reactions. The traditional school of thought is that they do so by binding to a target molecule to guide it along its potential energy surface. Given the enormous biochemical importance of these mechanisms, much research is focused on engineering enzymes, but often, human-made versions perform worse than natural ones. Is it possible that we are failing to account for the true reason some enzymes work? We propose to study whether strong light-matter coupling can occur in enzymes, as recent theoretical and experimental studies have shown that electromagnetic cavities can, in fact, change the potential energy surface of a molecule by shifting, adding, and removing surfaces and discontinuities, in turn modulating chemical reaction rates. Answering this question will require breakthroughs in theoretical formalisms, including beyond-dipole approximations, cavity-modulated intramolecular vibrational energy redistribution, and ab initio quantum electrodynamical electronic structure theories.
Entangled photons as signals for cellular receptors Entangled photons are used in quantum networking hardware to transport quantum information at the speed of light and to sense fields at lower limits than possible via classical means. Is it possible that analogous mechanisms exist in biological organisms to transport information faster and more precisely than electrical, chemical signals, or mechanical signals? Entangled states are delicate, so we first turn to entangled states of the photon field that interact weakly with the environment–photons with frequencies in the near-IR, for example, can travel for several centimeters within aqueous biological media. In addition, recent work in photonic cluster states shows that they can be quite resistant to environmentally-induced losses.
Long coherence times in disordered transition metal-protein complexes Anderson localization is a quantum effect in disordered media that results in spatial localization of particles and traditionally requires low-temperatures to be observed. Can this phenomenon be observed where the disordered medium is a protein and the localized particle is an electron, perhaps at the core of a transition metal-protein complex? Breakthroughs in intramolecular vibrational energy redistribution and open quantum systems will be required to understand the shuttling of energy in a protein.
