For most people, quantum mechanics is a topic that’s out on the fringes of what’s practical; it’s an area of study for people who like hard-to-prove theories and really difficult math problems. But get this: everything you touch, taste, see, smell, and hear is made up of quantum particles. And quantum particles can have quantum effects. In fact, a team of researchers may have triggered those effects in living organisms. Is it really possible to put bacteria in a state of quantum entanglement?
We Belong to the Light, We Belong to the Thunder
If you’ve ever heard of Schrödinger’s Cat, you’ve heard of quantum mechanics. That’s a thought experiment designed to illustrate the concept of quantum superposition. The idea is that if you put a cat in a box with a vial of poison that opens based on the spin of a quantum particle, the cat is both alive and dead — that is, in a state of superposition — until you open the box and check. Likewise, quantum particles can be in multiple states at once until they’re measured. That’s just one weird trick of the quantum world. Particles can also become entangled, meaning they’re linked so that they can affect each other’s quantum states — even if they’re at opposite ends of the universe.
But these effects are pretty much limited to the impossibly small particles of the quantum world like photons and electrons. As far as physics is concerned, there seem to be two sets of rules for two completely different worlds: the quantum world does one thing, and the macroscopic world we’re most familiar with does another. You’ve never accidentally entangled a pair of socks (if only!). But if there are two worlds with different rules that are only delineated by their size, then the obvious question is: where’s the line? Can a proton have quantum effects? A molecule? A single-celled organism?
Scientists are hard at work on that question, and they’ve come up with some enticing possible answers. A few years ago, scientists figured out that birds might use Earth’s magnetic field to navigate by sensing the quantum spin of electrons in their eyes. Scientists also think that our sense of smell depends on quantum vibrations of particles that enter our noses. Photosynthesis, bioluminescence, and really anything that involves turning light into energy or vice versa happens via quantum effects.
Quantum Gets Bigger
Which is precisely why, in 2016, David Coles from the University of Sheffield and his colleagues tried to get quantum effects from a photosynthetic organism. They squeezed several hundred photosynthetic bacteria into a cavity between two tiny mirrors spaced a few hundred nanometers apart, then bounced photons, or light particles, between the mirrors. Just as they had hoped, the bacteria’s light-sensitive molecules coupled with the energy in the cavity, making the bacteria absorb, emit, and reabsorb the photons.
But recently, another team led by quantum physicist Chiara Marletto of the University of Oxford took another look at Coles’ experiment and found that there was more to it than that. That team says the energy signature created matches what you might expect if the photosynthetic molecules had become entangled with the photons, specifically by photons both hitting and missing particular molecules at the same time.
You could, possibly, just interpret this as classical physics, with no quantum weirdness to blame. But the team found that a model based on classical physics (or semiclassical, since photons are by definition quantum) doesn’t match the actual results. That points to a stronger possibility that quantum entanglement really is what was going on in these bacteria. Whichever way it ends up, though, many researchers are working diligently to find the line between the classical and quantum worlds — if there is one at all.