麻豆淫院

The future of computing lies in the surprising world of quantum physics, where the rules are much different from the ones that power today's devices. Quantum computers promise to tackle problems too complex for even the fastest supercomputers running on silicon chips. To make this vision real, scientists around the world are searching for new quantum materials with unusual, almost otherworldly properties.

One of the more intriguing candidates is called a quantum spin liquid鈥攁 state of matter where electron spins never settle down, even at the coldest temperatures in the universe. To date, however, preparing such a quantum state in a lab has proven stubbornly elusive. In a collaborative project with multiple institutions, scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory now report coming tantalizingly closer.

As explained by Argonne Senior 麻豆淫院icist and Group Leader Daniel Haskel, in these materials, it's not atoms that stay fluid as in an ordinary liquid, but the tiny magnetic orientations鈥攐r spins鈥攐f electrons. Each spin wants to "get along" with its neighbors by aligning in a way that keeps everyone content. But when the spins are pushed closer together under pressure, satisfying every neighbor becomes impossible.

The result is a kind of magnetic deadlock鈥攃alled frustration鈥攊n which the spins can no longer settle into any fixed arrangement. The result is a continuous, entangled dance of fluctuating spins, even when cooled to near absolute zero.

"Achieving this quantum spin state would be a major milestone," said Eduardo Poldi, a graduate student at the University of Illinois Chicago in Professor Russell Hemley's group, with a joint appointment at Argonne. "Some types of quantum spin liquids could serve as a new platform for qubits, the basic building blocks of a quantum computer."

In their latest experiment at Argonne's Advanced Photon Source (APS), a DOE Office of Science user facility, the team turned their attention to a crystalline material thought to possibly have the ingredients for a spin liquid. It is an oxide containing sodium, cobalt and antimony (NCSO).

The material has special characteristics: Its cobalt atoms form a honeycomb pattern, like a beehive. That structure plays a key role. The electron spins tend to align perpendicular to the edges of each cell in the honeycomb, but at points where three edges meet, not all spins can align to satisfy their neighbors鈥攃reating a state of frustration.

Theoretical models predict that this frustration can host a quantum spin liquid with topological protection. In such a state, excitations can form that encode quantum information yet remain resistant to outside disturbance. That built-in protection could help protect fragile quantum states鈥攁n essential step toward stable quantum technologies.

In earlier work, Argonne researchers found that extreme pressure can serve as a control knob to induce quantum spin behavior. Using two flat diamonds to squeeze the electrons together in a magnetic crystal, they suppressed a material's usual magnetic order and nudged it toward a spin liquid state.

"Pressure provides a way to reduce the separation between atoms and their electrons," said APS 麻豆淫院icist Gilberto Fabbris. "By adjusting that distance, we can drive a magnetic crystal into a frustrated state. At a certain extreme pressure, magnetism disappears鈥攁nd a spin liquid emerges."

Achieving that state, however, is extraordinarily difficult. The pressure must be high enough to suppress magnetic order yet applied in a way that does not damage the crystal's internal symmetry. Using specialized diamond anvil cells at APS, the researchers were able to compress the NCSO to more than 1 million atmospheres鈥攔oughly 1,000 times the pressure at the bottom of the ocean鈥攁ll within a region smaller than the width of a human hair.

The team used three APS beamlines to analyze their NCSO sample from room temperature down to around absolute zero and from 1 to 1 million atmospheres. In particular, they performed X-ray diffraction and emission spectroscopy at beamlines 16-BM-D and 16-ID-D to unravel the atomic structure and electron spins of the NCSO over a wide range of temperature and pressure. They also used beamline 4-ID-D to track the changing magnetic properties.

Especially important, Poldi noted, was the ability at APS to measure the spin state within an atom and the spin-spin correlations between atoms under extreme pressures. The APS is the only facility in the United States where such an experiment is possible.

The results, now in Communications 麻豆淫院ics, indicate that the NCSO shows clear signs of approaching a spin liquid state, although the nature of the frustrated quantum state differs from the one predicted by theory.

That makes it a promising material for future studies鈥攁nd possibly, a stepping stone toward other honeycomb-structured materials that exhibit the strange properties of quantum materials. With the recent upgrade to the APS, researchers will be able to investigate candidate materials at five times higher pressures.

"Quantum spin liquids with topological protection provide an exciting path toward building qubits that are naturally shielded from outside interference," Haskel said. What began as a fundamental physics experiment may now point toward a new route for building more stable and fault-tolerant quantum technologies.