Even huge molecules follow the bizarre rules of the quantum world

Magnify a thousand times a grain of land and suddenly, it does not seem to respect the same rules. For example, its outlines will not be well defined most of the time and will look like a diffuse and sprawling cloud. This is the strange domain of quantum mechanics. "In some books you will find that a particle is simultaneously in different places," says physicist Markus Arndt of the University of Vienna in Austria. "That this really happens is a question of interpretation."

Another way of saying it: quantum particles sometimes act as scattered waves in space. They can touch and even get back on their own. But if you poke this wave-like object with certain instruments, or if the object interacts specifically with nearby particles, it loses its wave properties and begins to act as a discrete point – a particle. . Physicists have observed atoms, electrons and other minutiae making the transition between wave and particle-like states for decades.

But at what size do quantum effects no longer apply? What is the size of something and who can always behave as both a particle and a wave? Physicists have had difficulty answering this question because the experiments were almost impossible to conceive.

Now, Arndt and his team have bypassed these difficulties and have observed quantum wave properties in the largest objects to date – molecules made up of 2,000 atoms, the size of some proteins. The size of these molecules beats two and a half times the previous record. To see this, they injected the molecules into a tube 5 meters long. When the particles reach a target at the end, they are not just in the form of scattered points at random. Instead, they formed a pattern of interference, a striped pattern of dark and light stripes that suggests waves colliding and bumping into each other. They published the work today in Physical Nature.

"It's surprising that it works in the first place," says Timothy Kovachy of Northwestern University, who did not participate in the experiment. This is an extremely difficult experience, he explains, because quantum objects are delicate and suddenly move from their vague state to that of particles through interactions with their environment. The larger the object, the more likely it is that it hits something, warms up or even breaks, which triggers these transitions. To keep the molecules in a wave-like state, the team draws a narrow path through the tube, as if the police were going through a parade route. They keep the tube in a vacuum and prevent the entire instrument from oscillating, even with a spring and brake system. Physicists then had to carefully control the speed of the molecules so that they do not overheat. "It's really impressive," says Kovachy.