frequencies of vibrating bonds in odor- can distinguish between odorants con- synthesis could also contribute to such ant molecules.18 He argued that when an taining different isotopes.19 Two years widespread biological phenomena as odorant binds to a receptor, if its bonds later, other researchers failed to repro- vision and cellular respiration. Others are vibrating at a certain frequency they duce the results and called the theory have suggested that proton tunneling can facilitate the quantum tunneling “implausible.”20 But the idea didn’t go could promote spontaneous mutations of electrons within that receptor. This out of fashion. In 2016, another team in DNA, although theoretical work by transfer of electrons, according to his reported that honey bees can differ- Al-Khalili and colleagues suggest this model, triggers a signaling cascade in the olfactory neuron that ultimately sends an impulse to the brain. Now you’re not considered completely mad if Experimental evidence for the idea you say you’re studying quantum mechanics in is still elusive, says Jenny Brookes, a UCL physicist who has formulated the biology. It’s just considered a little bit wacky. problem mathematically to show that —Johnjoe McFadden, University of Surrey it’s theoretically feasible. “But that’s partly why it’s quite exciting.” In recent years, researchers have looked for iso- entiate odors with different isotopes,21 isn’t terribly likely, at least for the ade- tope effects similar to the ones found while a recent theoretical study pres- nine-thymine base pairs they modeled.23 in enzyme function. If tunneling plays ents a suite of new predictions to help Perhaps the most extreme exten- a substantial role, odorant molecules test the model’s validity.22 sion of quantum physics to the ani- containing heavier hydrogen isotopes Theoretical work is also driving mal kingdom is the idea that weird should smell different from normal ver- interest in quantum biological expla- quantum effects might play a role in sions due to the lower vibration frequen- nations with far less experimental sup- the human brain. University of Cali- cies of their bonds. port. For example, some researchers fornia, Santa Barbara, physicist Mat- The findings are mixed. In 2013, have speculated that the coherence thew Fisher has argued that neurons Turin’s group reported that humans effects posited to play a role in photo- possess molecular machinery capable

GLOSSARY: QUANTUM TERMINOLOGY The world at the scale of spinning atoms and subatomic particles is governed by the probabilistic rules of quantum mechanics, which often produce effects that seem counterintuitive to organisms living in a world usually described perfectly well by more-standard physics. These effects have been harnessed for multiple technological applications, and the possible role of quantum phenomena in several biological systems is now being explored.

ENTANGLEMENT: Two particles are said to be quantumly QUBITS: These units of information are the quantum entangled if their states are interdependent, regardless equivalent of standard binary digits or bits. While a bit of the distance separating them. In the classic example of can have a state of 0 or 1, qubits can have multiple states entanglement two entangled electrons, when measured, simultaneously, and may be entangled with other qubits to will have opposite spins. perform parallel computations. Qubits can be encoded in Important for: Quantum computing, quantum the spin states of electrons and other subatomic particles. cryptography Important for: Quantum computing Studied in: Photosynthesis, magnetoreception, human Studied in: Human consciousness consciousness COHERENCE: Because quantum objects can behave TUNNELING: Particles at the quantum scale have wave- like waves, they can exhibit a property of waves called like properties, and their exact location at any moment coherence when they are in a particular rhythm with one is described by a probabilistic wave function. As a result, another. Quantum coherence underlies several effects particles such as electrons can, with certain probabilities, observed by quantum physicists, including entanglement traverse—or tunnel through—apparently impermeable as well as interference patterns manifested as so-called energy barriers. quantum beating. Loss of coherence has traditionally been STAFF Important for: Thermonuclear fusion, scanning tunneling thought to happen very quickly in the molecular bustle of microscopy ambient- temperature environments. Studied in: Enzyme catalysis, photosynthesis, olfaction, Important for: Lasers, superconductors, quantum computing DNA mutation Studied in: Photosynthesis, magnetoreception, vision,

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