Qubits put new spin on magnetism: Boosting applications of quantum computers

"With the help of a quantum annealer, we demonstrated a new way to pattern magnetic states," said Alejandro Lopez-Bezanilla, a virtual experimentalist in the Theoretical Division at Los Alamos National Laboratory. Lopez-Bezanilla is the corresponding author of a paper about the research in Science Advances.

"We showed that a magnetic quasicrystal lattice can host states that go beyond the zero and one bit states of classical information technology," Lopez-Bezanilla said. "By applying a magnetic field to a finite set of spins, we can morph the magnetic landscape of a quasicrystal object."

"A quasicrystal is a structure composed by the repetition of some basic shapes following rules different to those of regular crystals," he said.

For this work with Cristiano Nisoli, a theoretical physicist also at Los Alamos, a D-Wave quantum annealing computer served as the platform to conduct actual physical experiments on quasicrystals, rather than modeling them. This approach "lets matter talk to you," Lopez-Bezanilla said, "because instead of running computer codes, we go straight to the quantum platform and set all the physical interactions at will."

The ups and downs of qubits

Lopez-Bezanilla selected 201 qubits on the D-Wave computer and coupled them to each other to reproduce the shape of a Penrose quasicrystal.

Since Roger Penrose in the 1970s conceived the aperiodic structures named after him, no one had put a spin on each of their nodes to observe their behavior under the action of a magnetic field.

"I connected the qubits so all together they reproduced the geometry of one of his quasicrystals, the so-called P3," Lopez-Bezanilla said. "To my surprise, I observed that applying specific external magnetic fields on the structure made some qubits exhibit both up and down orientations with the same probability, which leads the P3 quasicrystal to adopt a rich variety of magnetic shapes."

Manipulating the interaction strength between qubits and the qubits with the external field causes the quasicrystals to settle into different magnetic arrangements, offering the prospect of encoding more than one bit of information in a single object.

Some of these configurations exhibit no precise ordering of the qubits' orientation.

"This can play in our favor," Lopez-Bezanilla said, "because they could potentially host a quantum quasiparticle of interest for information science." A spin quasiparticle is able to carry information immune to external noise.

A quasiparticle is a convenient way to describe the collective behavior of a group of basic elements. Properties such as mass and charge can be ascribed to several spins moving as if they were one.