Physicists Just Gifted Us ‘Quantum Spin Liquid,’ A Weird New State Of Matter

A solid is made of particles that are, more or less, locked in an ordered framework. On the other hand, a fluid is made of particles that can flow freely around and past each other. However, imagine atoms that stay unfrozen, like those in a liquid– but which are in one constantly changing magnetic mess.

What you have then is one never-before-seen state of matter, one state of quantum weirdness called a quantum spin fluid. Now, by carefully manipulating atoms, scientists have managed to produce this state in the laboratory. The researchers released their work in the journal Science on December 2.

Scientists had discussed concepts about spin fluids for years. “However, we really got very interested in this when these philosophers, here at Harvard, finally discovered a way to, in fact, generate the quantum spin liquids,” states Giulia Semeghini, a physicist and also postdoc at Harvard College, who coordinated the research project and was one of the paper authors.

Under severe problems not typically found on Earth, the rules of quantum mechanics can twist particles into all sorts of exotica. Take, for example, degenerate matter discovered in the hearts of dead stars like white dwarfs or neutron stars, where extreme pressures cook particles into slurries of subatomic particles. Or for another, the Bose-Einstein condensate, in which multiple particles at extremely low temperatures sort of merge together to behave as one (its creation won the 2001 Nobel Prize in Physics).

The quantum spin fluid is the latest entry in that bestiary of cryptid states. Its atoms do not freeze into any sort of ordered state, and they’re constantly in flux.

The “spin” in the name refers to one property inherent to each particle– either up or down– which gives rise to magnetic fields. In a normal magnet, all the rotates point up or down in a careful order. In a quantum spin fluid, on the other hand, there’s a 3rd spin in the image. This prevents coherent magnetic fields from creating.

This, combined with the esoteric rules of quantum mechanics, means that the rotates are constantly in different positions at once. If you observe at just a few particles, it’s hard to tell whether you get a quantum fluid or, if you do, what properties it has.

Quantum spin liquids were 1st theorized in 1973 by a physicist called Philip W. Anderson, and physicists have been trying to have their hands on this matter ever since. “Many different experiments … tried to develop and observe this kind of state. But this has really turned out to be extremely challenging,” says Mikhail Lukin, a physicist at Harvard College and one of the paper’s authors.

The researchers at Harvard had a new device in their collection: what they call a “programmable quantum simulator.” Essentially, it is a machine that allows them to play with individual atoms. Researchers can shuffle atoms around a two-dimensional grid-like magnet on a whiteboard using specifically focused laser beams.

” We could control the position of each atom individually,” states Semeghini. “We could position them individually in any shape or form that we want.”

Furthermore, to really determine if they had successfully created a quantum spin liquid, the scientists took advantage of something called quantum entanglement. They energized the particles, which started to interact: changes in the property of one particle would reflect in another. By looking at those connections, the scientists discovered the confirmation they required.

All this might appear like creating abstract matter for abstract matter’s sake– but that is part of the appeal. “We can kind of touch it, poke, play with it, even in some forms talk to this state, manipulate it, and make it do what we want,” states Lukin. “That’s what’s really exciting.”

But researchers do think quantum spin liquids have essential applications, too. Simply venture into the realms of quantum computers.

Quantum computer systems have the potential to far outstrip their conventional counterparts. Compared to computers today, quantum computers can create better simulations of systems such as molecules and, much more rapidly, complete specific calculations.

But what researchers use as the building blocks of quantum computers could leave something to be desired. Those blocks, dubbed qubits, are often things like individual particles or atomic nuclei– which are sensitive to the slightest bit of sound or temperature fluctuations. Quantum spin liquids could be less finicky qubits with information kept in how they’re arranged.

If researchers could demonstrate that a quantum spin liquid could be used as a qubit, says Semeghini, it could lead to an entirely recent sort of quantum computer.

Reference: G. Semeghini et al. Probing topological spin liquids on a programmable quantum simulator. DOI: 10.1126/science.abi8794

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