Quantum biology is an emerging field exploring whether quantum mechanical effects — coherence, tunneling, and entangled radical pairs — play functional roles inside warm, noisy biological organisms. Classical physics assumed quantum effects couldn’t survive such environments; the findings of quantum biology challenge that assumption.
## Quantum Coherence in Photosynthesis
In 2007, Graham Fleming’s group published a landmark Nature paper using two-dimensional electronic spectroscopy to detect quantum coherence oscillations lasting approximately 300 femtoseconds in the FMO (Fenna-Matthews-Olson) light-harvesting complex of green sulfur bacteria.
The provocative interpretation: photosynthesis might use quantum superposition to simultaneously explore multiple energy transfer pathways, collapsing to the most efficient route — analogous to quantum parallel computation. This claimed to explain photosynthesis’s near-100% energy transfer efficiency.
Subsequent work (2010s–2020s) has complicated the picture: some coherence signals appear to arise from nuclear vibrations rather than electronic quantum coherence, and whether these effects are functionally relevant at physiological temperatures in living cells remains contested. See the [Nature Chemistry review](https://www.nature.com/articles/s41557-021-00753-8).
## Quantum Tunneling in Enzyme Catalysis
Quantum tunneling allows particles to cross energy barriers classically forbidden to them. In enzyme-catalyzed hydrogen transfer reactions, the evidence for quantum tunneling is relatively solid:
In enzymes including alcohol dehydrogenase and dihydrofolate reductase, hydrogen transfer rates substantially exceed classical Arrhenius equation predictions, with kinetic isotope effects (comparing hydrogen vs. deuterium) characteristic of quantum tunneling. Tunneling may account for 10–100-fold rate enhancements over classical transition-state theory.
## Radical Pairs and Bird Navigation
The European robin navigates thousands of kilometers using Earth’s magnetic field. Klaus Schulten proposed in 1978 that light activates cryptochrome proteins in the retina, creating correlated electron spin pairs. Earth’s magnetic field influences the quantum state evolution (singlet vs. triplet) of the radical pair, changing chemical product ratios and generating a magnetic signal detectable by the nervous system.
The radical pair mechanism has the strongest experimental support in quantum biology: cryptochrome magnetic sensitivity has been demonstrated behaviorally and cellularly, and migratory bird magnetoreception is light-dependent (consistent with cryptochrome photoactivation). Whether quantum entanglement is directly involved remains open.
See [Quantum Sensing](https://sunqi.org/quantum-sensing-en/) and the [Nature Physics review on quantum biology](https://www.nature.com/articles/s41567-021-01318-9).
—
