Ninety-Nine Percent

Quantum mechanics belongs to laboratories, vacuums, and temperatures at which atoms stop trembling — in short, to conditions that simply can’t exist inside a living organism. Right?

Wrong — and the green sulfur bacterium from a hot spring stands ready to demonstrate this neatly.

The green sulfur bacterium — a creature so primitive that it has no brain, no nervous system, and not even a nucleus in its cell. It lives in hot springs, feeds on light and hydrogen sulfide, and its single job is to convert photons into energy. Photosynthesis.

In 2007, Greg Engel and his team at Berkeley (Nature) discovered that this bacterium does its photosynthesis quantum-mechanically.

Specifically: inside the bacterium there is a protein “antenna” (physicists call it FMO — after the surnames of the people who described it). The antenna catches sunlight and passes its energy onward, into the “reactor.” And it does this quantum-mechanically: the energy doesn’t hop from molecule to molecule like a ball bouncing down stairs. It tries all paths simultaneously — as if the ball were rolling down every staircase at once and “choosing” the fastest route. Physicists call this “quantum coherence” — a state in which the system behaves as a single whole rather than a collection of separate parts. Transfer efficiency — around 99%.

Ninety-nine percent. The best solar panel we know how to build — about 47% (multilayer, lab-grade, costing several thousand dollars per square centimeter). A brainless bacterium — 99%, on a protein that costs nothing and is produced for free in any hot spring.

The natural question follows: how does it manage this?

---

The standard answer of physics before 2007 ran as follows: impossible. Quantum coherence is a thing that exists at temperatures near absolute zero ($-273{}^{\circ }$C), in a vacuum, under ideal laboratory conditions. In a “warm and wet” biological environment — at 37 degrees, in water, surrounded by billions of molecules that constantly jostle the quantum system and break coherence (physicists call this “decoherence” — the decay of a quantum state from collisions with the environment) — quantum effects should vanish in one ten-trillionth of a second. That is a million times faster than a blink, and faster than anything biology could make use of — or so it was thought.

Max Tegmark at MIT calculated this in 2000 and delivered his verdict: quantum effects in the brain (and in biology in general) are impossible — too warm, too wet, too noisy.

And then Engel showed up — and a bacterium that couldn’t have cared less about Tegmark’s calculations.

---

Quantum biology is a field that exploded after 2007: four confirmed phenomena, each astonishing on its own, and together they break one of the chief convictions of twentieth-century physics.

First: photosynthesis.

Imagine the task: you need to pass a ball from one end of a stadium to the other. On the field — a thousand players placed at random. The classical approach: the ball hops from one nearest player to the next. Slow, inefficient, with losses at every bounce.

The quantum approach is arranged differently: the ball tries all routes simultaneously, in superposition, and “picks” the fastest one. The word “tries” here works in the literal sense, without any metaphorical discount.

This is what the FMO complex does — the protein “antenna” in the green sulfur bacterium. Engel and his team at Berkeley (Nature, 2007) found quantum coherence in the process of energy transfer from the antenna to the reaction center. The exciton — a quantum of energy — doesn’t hop from molecule to molecule. It exists on all molecules simultaneously and “collapses” onto the optimal route.

How does the bacterium maintain coherence? At room temperature, quantum states decohere in femtoseconds (${10}^{-15}$ s) — a billion times faster than a blink. The answer is counterintuitive: it’s the noise of the environment that helps. The vibrations of the protein “frame” in which the FMO sits sustain coherence. As if you had learned to surf the waves of decoherence instead of drowning in them.

Obviously, somebody “learned” this — over three and a half billion years of evolution, or, more precisely, of learning.

Subsequent work (Cao et al., Science Advances, 2020) refined the picture: coherence is real, while its role in efficiency is a matter of debate. But the fact itself is beyond dispute: quantum effects exist and function in biology at room temperature.