Stimulating applications of quantum computers

Research using a quantum computer as the physical platform for quantum experiments has found a way to design and characterize custom magnetic objects using quantum bits or qubits. This opens up a new approach to developing new materials and robust quantum computing.

“Using a quantum annealer, we demonstrated a new way to model magnetic states,” said Alejandro Lopez-Bezanilla, a virtual experimenter in the theoretical division at Los Alamos National Laboratory. Lopez-Bezanilla is the corresponding author of a paper on the research Scientific progress.

“We have shown that a magnetic quasicrystal lattice can accommodate states beyond the zero and one bit states of classical information technology,” Lopez-Bezanilla said. “By applying a magnetic field to a finite series of spins, we can change the magnetic landscape of a quasicrystal object.”

“A quasicrystal is a structure composed by the repetition of some basic shapes according to rules different from those of ordinary crystals,” he said.

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

The ups and downs of qubits

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

Since Roger Penrose designed the aperiodic structures named after him in the 1970s, no one had twisted each of their nodes to observe their behavior under the influence of a magnetic field.

“I connected the qubits so that they all together reproduced the geometry of one of his quasicrystals, called P3,” Lopez-Bezanilla said. “To my surprise, I noticed that applying specific external magnetic fields to the structure caused some qubits to exhibit both up and down orientations with the same probability, giving the P3 quasicrystal 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 into a single object.

Some of these configurations do not show a precise order of the orientation of the qubits.

“This could play to our advantage,” Lopez-Bezanilla said, “because they could potentially host a quantum quasi-particle of interest to information science.” A spin quasiparticle can convey information that is 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 attributed to multiple spins moving as if they were one.