Research using a quantum computer as a physical platform for quantum experiments has found a way to design and characterize individual magnetic objects using quantum bits, or qubits. This opens up a new approach to developing new materials and reliable quantum computing.
“Using quantum annealing, we have demonstrated a new way to pattern magnetic states,” said Alejandro López-Bezanillo, a virtual experimenter in the Theory Division at Los Alamos National Laboratory. López-Bezanilla is the corresponding author of the study article in Achievements of science.
“We have shown that a magnetic quasi-crystalline lattice can accept states that go beyond the zero and one-bit states of classical information technology,” López-Bezanillo said. “By applying a magnetic field to a finite set of spins, we can change the magnetic landscape of a quasi-crystalline object.”
“A quasi-crystal is a structure that consists of the repetition of certain basic shapes according to rules that are different from those of ordinary crystals,” he said.
For this work with Cristianu Nisali, a theoretical physicist also at Los Alamos, the D-Wave quantum annealing computer served as a platform for conducting actual physical experiments on quasicrystals rather than simulating them. This approach “allows matter to talk to you,” López-Bezanillo said, “because instead of running computer codes, we go straight to the quantum platform and set up all the physical interactions at will.”
The ups and downs of qubits
López-Bezanillo selected 201 qubits on a D-Wave computer and connected them together to reproduce the shape of a Penrose quasicrystal.
Since Roger Penrose conceived the periodic structures that bear his name in the 1970s, no one has twisted each of their nodes to observe their behavior under the influence of a magnetic field.
“I connected the qubits so that together they reproduce the geometry of one of his quasicrystals, called P3,” said López-Bezanilla. “To my surprise, I noticed that applying specific external magnetic fields to the structure causes some qubits to exhibit both up and down orientations with equal probability, causing the P3 quasicrystal to adopt a rich variety of magnetic shapes.”
Manipulating the strength of the interaction between qubits and qubits with an external field causes the quasicrystals to arrange themselves in different magnetic structures, offering the prospect of encoding more than one bit of information in a single object.
Some of these configurations do not show a clear order of orientation of the qubits.
“This could work in our favor,” López-Bezanillo said, “because they could potentially contain a quantum quasiparticle of interest for computer science.” A spin quasiparticle is capable of carrying information that is immune to external noise.
A quasiparticle is a convenient way to describe the collective behavior of a group of fundamental elements. Properties such as mass and charge can be attributed to multiple spins moving as if they were one.