For a hundred years, all known particles had only two identities: bosons, fermions.

Bosons can be stacked together in an infinite number of numbers, while fermions cannot coexist in a quantum state. The laser relies on bosons, and the electronic shell relies on fermions. This is the most fundamental split of quantum mechanics.

But now, someone has found the "third particle". First Name:类粒子（paraparticles）。

Not bosons, not fermions.

It is not a pure particle of matter, nor is it a medium of force, but a hidden state that quantum mechanics allows to exist but has never been found. They may live inside the material, existing in a peculiar commutative symmetry. They have "hidden internal variables" that are swapped not with just a positive or negative sign, but with the entire structure changing.

This theory was not proposed by some fanciful philosopher, but by the team of Zihyuan Wang of the Max Planck Institute for Quantum Optics in Germany.

It all started in 2021, when he was a graduate student at Rice University. A chance mathematical derivation made him realize that he might have hit a forgotten corner of physics.

At that time, he took this idea to his mentor, Kaden Hazzard. The other party's first reaction was: "I'm not sure if this thing is reliable, but if you really believe it, just put everything else down and do your best to do this." ”

Three years later, they actually published their papers.

Published in Nature, the theory is rigorous, the mathematics is closed, and the physical picture is clear. What's more, it breaks down something that was thought to be a foregone conclusion: the DHR theorem.

In the 1970s, Doplicher–Haag–Roberts proposed a series of mathematical frameworks to prove that in the case of satisfying the hypotheses of "locality" and "three-dimensional space",Only bosons and fermions can exist in nature。

This has almost "blocked" particles-like from their physical legitimacy for decades.

But Wang's team found that DHR's assumptions were far more harsh than people thought. In particular, the point of "complete indistinguishability" does not necessarily hold true in certain superimposed states.

Their particle-like model abandons the absolute requirement of "no difference" – that is,If two observers share information, they can tell if a particle has been exchanged。

That's where the breaking point is.

The traditional particle exchange will not affect the experimental statistical results, but after the exchange of particles, they will "link" each other's hidden properties. These properties are not detectable on their own, but the correlation of data between multiple observers can reveal this information.

This puts the particle-like into an interesting position:

It's not a random pile like bosons, and it's not mutually exclusive like fermions.

Rather, it's finite and stackable.

You can pile a little, but if you pile more, it will "burst" and you have to enter a new state. How many can be stacked depends on the details of the model. Each type of particle has a different degree of crowding.

Physicists are accustomed to a bipolar world. Now, the middle ground has to be inserted.

Theories predict that these class particlesMost likely to appear as a "quasiparticle" in some exotic materials。 That is, they are a manifestation of the collective excited state in the material, not free particles. Similar to phonons, excitons, and anyons, these are the "second generation of particles" that have entered the laboratory.

Any anyon proposed by Frank Wilczek in the 1980s has now been confirmed in quantum Hall materials and is even being applied to the architecture of fault-tolerant quantum computing.

Array with Rydberg atoms.This is one of the most powerful quantum simulation platforms available, using the extreme amplified orbits of the outer electron transitions of atoms to achieve extremely high responses to electric fields. Such systems are already being used to simulate anyons and may be the main battleground for implementing particle-like objects.

The most surprising thing is that the team of Markus Müller, another researcher, is working on particles almost at the same time. They took a different approach—reinterpreting the constraints of DHR and defining "indistinguishability" from the perspective of multiple observers of quantum superposition, which in turn "ruled out" the possibility of particle-like existence.

The theories of the two sides do not conflict, but complement each other.

In terms of physical images, particle-like images are more like a dynamic network of interactions. Swapping positions is not a minus sign, but like an operating system upgrade, which affects not only the participants themselves, but also a series of subsequent evolutions.

This makes it easier to describe certain quantum phase transition models, entangled state structures, and possibly in particle-like frameworks.

Even, it is possibleA new class of quantum materials has been born。 And it's three-dimensional, unlike anyon, which can only live in two dimensions.

This means that theyThere is a better chance of entering engineering applications。 For example, materials designed with particle-like properties may exhibit behaviors that are not possible with boson or fermion materials in terms of density of states, spin coupling, and charge transport.

In the past we crammed the world into two boxes: you can either stack or you can't. Now, the seam between the two boxes has opened a seam.