How plants can perform feats of quantum mechanics

It’s spring now in the Northern Hemisphere, and the world around us is green. Outside my window, trees are full of leaves that act like miniature plants, collecting sunlight and turning it into food. We know this basic transaction takes place, but how does photosynthesis really happen?

During photosynthesis, plants use quantum mechanical processes. In an effort to understand how plants do this, Scientists at the University of Chicago He recently modeled how leaves work at the molecular level. They were astonished by what they saw. It turns out that plants behave like a strange fifth state of matter known as a Bose-Einstein condensate. Even stranger, these condensates are usually found at temperatures close to absolute zero. The fact that they are around us on a normal, mild spring day is a real surprise.

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The three most common states of matter are solid, liquid and gas. When pressure or heat is added or removed, matter can transition between these states. We often hear that plasma is the fourth state of matter. In plasma, atoms dissolve into a soup of positively charged ions and negatively charged electrons. This usually happens when the material gets too hot. The Sun, for example, is mostly a large ball of superheated plasma.

If matter can be very hot, it can also be supercooled, causing particles to fall into very low-energy states. Understanding what happens next requires some knowledge of particle physics.

There are two main types of particles, bosons, and fermions, and what sets them apart is a property called spin—a curiously mechanical property related to the angular momentum of a particle. Bosons are particles with integer spins (0, 1, 2, etc.), while fermions have half integer spins (1/2, 3/2, etc). This property has been described before Spin statistics theory, which means if you swap two bosons, you will keep the same wave function. You can’t do the same thing with fermions.

in Bose-Einstein condenser, the bosons within a substance have such low energy that they all occupy the same state, acting as a single particle. This allows quantum properties to be seen on a macroscopic scale. a Bose-Einstein condenser It was created in a laboratory for the first time in 1995, at a temperature of no more than 170 nanokelvins.

Quantitative photosynthesis

Now, let’s take a look at what happens in a typical leaf during photosynthesis.

Plants need three basic ingredients to make their own food – carbon dioxide, water and light. A pigment called chlorophyll It absorbs energy from light in red and blue wavelengths. It reflects light in other wavelengths, which makes the plant appear green.

On a molecular level, things get a lot more interesting. The absorbed light excites an electron within the chromophore, which is a part of the molecule that determines its reflectance or absorption of light. This starts a series of chain reactions that end up producing sugars for the plant. Using computer modeling, researchers at the University of Chicago examined what was happening in green sulfur bacteria, a photosynthetic microbe.

Light excites an electron. Now the electron and the empty space it left behind, called the hole, work together as a boson. This electron-hole pair is called an exciton. The exciton travels to deliver energy elsewhere, where sugars are created for the organism.

“Chromophores can transfer energy between them in the form of excitons to an interaction center where the energy can be used, like a group of people passing a ball to a target,” Anna Scottin, the study’s lead author, explained to Big Think. .

Scientists have discovered that the paths of excitons within the localized regions are similar to those seen inside an exciton condenser – a Bose-Einstein condensate made of excitons. The challenge with exciton capacitors is that electrons and ions tend to recombine quickly. Once this happens, the exciton vanishes, often before a capacitor can form.

It’s very difficult to create these condensates in the lab, but they were here, right in front of scientists’ eyes, in a chaotic organism at room temperature. Through condensed formation, the excitons formed a single quantum state. In essence, they acted like a single particle. This forms a superfluid – a fluid without viscosity and without friction – allowing energy to flow freely between the chromophores.

Their results have been published in PRX Energy.

chaotic conditions

Excitons usually decay quickly, and when they do, they can no longer transfer energy. To give them a longer life, they usually need to be kept very cold. In fact, exciton capacitors have never been seen before above temperatures of 100 K, which is a lukewarm minus 173 degrees Celsius. This is why it is so surprising to see this behavior in a truly chaotic system at normal temperatures.

So what is going on here? Just another way that nature constantly surprises us.

“Photosynthesis works at normal temperatures because nature has to work at normal temperatures to survive, so the process evolved to do that,” says Schotten.

In the future, room temperature Bose-Einstein condensates may have practical applications. Because they act like a single atom, Bose-Einstein condensates may give us insight into quantum properties that are difficult to observe at the atomic level. They also have apps for gyrosAnd Corn laserAnd Highly accurate time, gravity or magnetic sensorsAnd Higher levels of energy efficiency and transmission.