快猫短视频

Exotic theoretical particles known as fractons have until now remained imaginary constructs. But new research suggests they may have been lurking under our noses within a certain kind of defect in crystals. The findings could one day help us build memory storage for quantum computers.

In 2011, Jeongwan Haah, then a graduate student at the California Institute of Technology in Pasadena, California, discovered a new theoretical phase of matter composed of particle-like entities he dubbed 鈥榝ractons.鈥�

Fractons are characterised by how they move 鈥� or don鈥檛. A single fracton on its own is completely immobile, but introduce a second one in the same material and the two are suddenly able to move along a line. For four fractons to move, they must remain equally spaced from one another at the corners of a quadrilateral shape like a cube. Because each only has the power to move with others, they are a bit like fractions of a particle, earning them their name.

When he first heard about the concept, says at the University of Colorado Boulder, fracton models sounded so complicated that he thought he鈥檇 never completely understand them. But soon after, he says, 鈥淚 realised that I know a system which exhibits exactly those properties.鈥�

Fill in the blank

Radzihovsky studies crystals, which have regularly-spaced arrangements of atoms. Crystals can have defects, like a missing atom that leaves a hole in the lattice. Jiggle a crystal enough, and another atom can be knocked into the hole. The fallen atom leaves behind its own empty space, so the hole will appear to move.

But certain types of crystal defects can鈥檛 be moved in this way. Picture a square grid of atoms, remove a corner quadrant, and then bend the remaining atoms toward one another so they form a triangle. The atoms surrounding the imperfection all remain bonded to one another. No matter how much you shake such an arrangement, there is no mobile hole that can go wandering around within this crystal. This immobility is similar to that of a single fracton.

A grid can contain two such defects, with a triangle-shaped imperfection near a pentagon-shaped one 鈥� the triangle is missing an atom, while the pentagon has an extra one. The entire grid now has some wiggle room that can result in atoms unbonding and rebonding with their neighbors. The two defects will remain somewhere in the grid but can now move together either left or right but not up and down, much like the highly-constrained motion of two fractons.

, who works with Radzihovsky, used a branch of mathematics called tensor gauge theory to prove that crystal defects and fractons were not just similar, but mathematically equivalent.

Quantum memory

鈥淚t showed a connection between something that was purely theoretical to something that鈥檚 ordinary and well understood,鈥� says at the University of Toronto in Canada, who was not involved in the work.

Because this work can allow researchers to study how fractons would behave if they were made real, it could unlock ways to build quantum hard drives. In classical computers, electrons store information by being positioned as either a zero or one. Should one electron spontaneously flip, the electromagnetic attraction of its neighbours will usually help realign it.

But in quantum computers, particles are kept in superpositions of zeros and ones and are usually highly entangled with their neighbors. An unprompted change of one quantum bit 鈥� or qubit 鈥� could flip its superposition and create a cascading effect on the other qubits, potentially resulting in useless computations.

Physicists have been looking for quantum particles resistant to such changes. And fractons, with their extremely limited mobility, seem to fit the bill. Slagle thinks that engineers are pretty far from using this new knowledge to build quantum computer memory. Even so, he finds the work impressive for how many disciplines it brings together. 鈥淚t鈥檚 kind of like finding some crack in physics that extends pretty deep into everything.鈥�

Read more: World鈥檚 first time crystals cooked up using new recipe