Physicists from Harvard University have documented a new state of matter which could significantly advance quantum technology, according to a new paper published in the peer-reviewed journal Science earlier this month.
The state of matter they found is called quantum spin liquid, which has special properties that produce long-range quantum entanglement — a phenomenon in which particles' states are connected even when the particles are separated by distance.
Quantum spin liquid was first predicted by physicist Philip W. Anderson about 50 years ago, in 1973, but has never been observed in experiments.
The Harvard researchers decided to take a new approach and tried creating the state of matter instead of trying to find it in existing systems.
"A few theorists at Harvard came up with an idea on how to actually create this phase, instead of in the usual setting where it was looked for, which were basically solid systems — condensed-matter systems — how we could recreate it using our atoms," Giulia Semeghini, a postdoctoral fellow in the Max Planck-Harvard Research Center for Quantum Optics and lead author of the study, told The Harvard Crimson.
The researchers decided to use a "programmable quantum simulator," a quantum computer that uses lasers to reproduce a physical setting and manipulate atoms in order to successfully recreate quantum spin liquid. The simulator allows them to position and shape atoms in any form they want.
A quantum spin liquid has magnetic properties, as its atoms become entangled and the material fluctuates and changes. While, in a normal magnet, all the electron spins align into large-scale patterns like the stripes of a checkerboard, quantum spin liquids have a third spin which creates a triangular pattern or lattice, according to Cosmos magazine. This difference prevents the spins from stabilizing in any particular direction, with the three electrons constantly forcing each other to switch their spin direction.
The researchers used the simulator to create the lattice pattern, placed atoms in it and watched them interact and entangle.
Standard quantum computers run based on "qubits" — quantum bits — which are very fragile against external effects. Quantum spin liquids could change that, allowing the creation of a "topological qubit" which stores information in the shape of a system, instead of in the state of a single particle, Semeghini told The Harvard Crimson.
Since the topology is very hard to break, such a qubit would be very resistant to error.
"That is a dream in quantum computation," says Semeghini to Cosmos. "Learning how to create and use such topological qubits would represent a major step toward the realization of reliable quantum computers."
Physics professor Mikhail Lukin, senior author of the study and co-director of the Harvard Quantum Initiative, told The Harvard Crimson that these qubits could be used to build a quantum computer that is "masked to errors," cautioning that the team has only created a "baby version" of topological qubits, so far.
"It’s very much fundamental physics, still, what we’re doing," said Lukin. "But the fact that we can create such states, and we can really play with them, we can poke at them, we can actually kind of talk to them and see how they respond — this is what’s exciting."
The breakthrough comes just days after two teams of researchers published papers on their discoveries of "time crystals," a new phase of matter which repeats in time in a manner similar to the way a regular crystal's structure repeats in space. The particles in the crystal perpetually switch between two states without requiring the input of more energy and without losing any energy.