Spooky action at a distance. Wave-particle duality. Schrodinger’s cat. All these quantum phenomena are, if not fully understood, at least well-documented. And in the end they only matter at the small scale. We don’t expect to see a cat both dead and live in our backyard.
But what if some quantum phenomena could extend way beyond the small distances of the quantum realm?
This is exactly what happens in the so-called Efimov state. Discovered in 1970 by Efimov, this prediction was largely ignored until it become a hot topic in 2006 when it was observed experimentally.
Under special conditions, a trio of particles - specifically bosons - can exhibit an infinite number of bound states. While interesting in itself, what makes these states especially interesting are their scale. Each state differs by a factor ~22, growing exponentially in size. In particular, the size of each Efimov state becomes much larger than the interaction distance between the individual particle pairs. And these states could, in principle, take an arbitrary size (however, the states also become weaker as their size increase).
Another notable aspect of the Efimov states are their universality: Efimov states occur regardless of the underlying physical interactions between particles. In fact, it doesn’t matter whether the particles are molecules, atoms, or nuclei.
The Efimov state is fascinating due its wild and outlandish nature. This of course begs the question: Are there other arrangements of forces or particles that extend beyond the quantum realm?1 And could some of these play a role at our classical scale, influencing the behavior of matter?
Further reading
- Efimov Physics: a review, Rep. Prog. Phys. 80 056001 (2017)
- Physicists Prove Surprising Rule of Threes, Natalie Wolchover
Other quantum phenomena that manifest at the “classical” scale include supraconductivity or superfluidity. These states of matter however require special conditions such as ultra-low temperature to occur. ↩︎
