Tackling quantum many-body states using an atomically precise, bottom-up approach

FEBRUARY 12, 2021

Using the breakthrough ESR-STM technique, researchers from the IBS Center for Quantum Nanoscience in a US-based collaboration constructed quantum-mechanically coupled artificial spin chains to reveal their quantum many-body states, including the resonating valence bond state.
Nanotechnology has traditionally pursued a top-down approach toward engineering and miniaturization, however, it faces a minimum size limit of a few atoms due to the emergence of dominant quantum effects at that scale. The scanning tunneling microscope (STM), with its unprecedented spatial resolution and absolutely precise manipulation of individual atoms, allows researchers to flip the paradigm into a bottom-up approach to engineer artificial structures at the real atomic scale. Furthermore, an STM equipped with electron spin resonance (ESR-STM) provides a breakthrough in the field of nanoscience by allowing the precise quantum control of individual atomic spins.

“Building artificial structures by placing one atom at a time remains a technical marvel. By using that ability to engineer controlled systems of electronic spins opens many possibilities to perform experimental modeling that furthers the understanding of hardcore physics at the heart of basic science,” states Andreas Heinrich, Director of the IBS Center for Quantum Nanoscience (QNS).

In a study published in Nature Communications on February 12, 2021, researchers from QNS in a US-based collaboration, constructed artificial quantum spin arrays on a surface using an STM. The team engineered the quantum states of the spin arrays using a tunable atomic-scale magnetic field emanating from the STM tip then measured their quantum many-body states at sub-atomic resolution using electron spin resonance.

These coupled spins featured strong quantum fluctuations due to antiferromagnetic exchange interactions between neighboring atoms. Atom-selective ESR measurements on the spin arrays gave access to properties of exotic quantum many-body states, such as a finite-size realization of a resonating valence bond state. “These spin arrays provide a versatile quantum-matter toolkit with atom-selective measurements, which allows highly entangled quantum states to be generated and probed in detail,” said Kai Yang at IBM.

Atomic-scale experimental modeling of coupled spin systems, enhanced by atom-selective ESR-STM measurements, opens a new avenue to explore nanoscale spin science,” said Soo-hyon Phark of QNS. “This bridges the physics of individual atoms and macroscopic objects that may provide microscopic understanding of exotic physical phenomena such as spin liquid and high temperature superconductivity, as well as provide a platform to design well-defined atomic scale spintronic devices.".

Probing resonating valence bond states in artificial quantum magnets

Kai Yang, Soo-Hyon Phark, Yujeong Bae, Taner Esat, Philip Willke, Arzhang Ardavan, Andreas J. Heinrich and Christopher P. Lutz

Nature Communications 12, 993 (2021)