Empa Breakthrough: Nanographene “Quantum Lego” Brings Heisenberg’s Theories to Life in New Spin Chain Models

Molecular Lego bricks: For the homogeneous Heisenberg chain, the researchers used the nanographene molecule Olympicene, which consists of five carbon rings. Image: Empa

(IN BRIEF) Empa researchers from the nanotech@surfaces laboratory have experimentally recreated two fundamental quantum physics models originally inspired by Werner Heisenberg using innovative “quantum Lego” constructed from nanographenes. Building on a previous success with the alternating Heisenberg model, the team, led by Roman Fasel, has now also realized a homogeneous Heisenberg chain, demonstrating distinct quantum properties such as strong spin entanglement and long-range correlations. Their meticulous work, which confirms longstanding theoretical predictions, is documented in Nature Materials and represents a significant step towards developing a versatile material platform for experimental quantum technology research that could pave the way for practical applications in communication, computing, and measurement.

(PRESS RELEASE) DÜBENDORF, 14-Mar-2025 — /EuropaWire/ — Empa, the Swiss research institute for applied materials sciences and technology, announces that its researchers from the nanotech@surfaces laboratory have successfully brought to life another foundational theoretical model from quantum physics, originally proposed by Nobel laureate Werner Heisenberg. Their breakthrough experiment relied on a type of “quantum Lego” constructed from minuscule carbon molecules known as nanographenes. This synthetic, bottom-up approach paves the way for versatile experimental investigations in quantum technologies, potentially fueling future breakthroughs in the field.

In a landmark achievement in 2024, Empa scientists and their collaborators first realized a one-dimensional alternating Heisenberg model using synthetic materials—a quantum-physical framework that has been studied for nearly a century. This model describes a linear chain of spins, serving as a basis for understanding quantum magnetism. Building on this success, the team, led by Roman Fasel, head of the nanotech@surfaces laboratory, has now recreated a closely related variant in the laboratory.

Unlike the alternating model, where spins are connected by alternating strong and weak interactions, the new model features spins that are uniformly coupled. Although this difference may seem subtle, it leads to fundamentally distinct physical properties. In the homogeneous chain, spins are highly entangled and display long-range correlations, with no energy gap between the ground state and excited states. Conversely, the alternating chain develops an energy gap and its spins tend to form tight pairings with correlations that decay rapidly. The researchers have meticulously validated these theoretical predictions using nanographene-based spin chains, with their findings published in the latest edition of Nature Materials.

Both quantum models were realized using nanographenes—tiny, precisely engineered fragments of the two-dimensional material graphene. By carefully controlling the shapes of these fragments, the team can tailor their quantum physical properties. Their ultimate goal is to develop a material platform—a kind of “quantum Lego”—that will enable the experimental study of a broad array of quantum models and phenomena.

The two experiments underscore this innovative strategy. For the alternating spin chain, the researchers employed Clar’s goblets—hourglass-shaped nanographene molecules composed of eleven carbon rings. In contrast, the homogeneous Heisenberg chain was constructed using Olympicene, a nanographene consisting of five rings whose design is inspired by the Olympic rings.

Atomic precision: Microscopy images of the homogeneous Heisenberg chain made of Olympicene; top: atomic force microscopy, bottom: scanning tunneling microscopy. Image: Empa

“We have now demonstrated for the second time that theoretical models in quantum physics can be realized with nanographenes, allowing us to put their predictions to the test experimentally,” says Fasel. Looking ahead, the research team plans to use their nanographene “building blocks” to create and study ferrimagnetic spin chains, where magnetic moments align antiparallel without completely cancelling each other out. They are also keen to explore two-dimensional spin lattices, which promise an even richer variety of phases—including topological states, quantum spin liquids, and exotic critical phenomena—making them highly relevant for both fundamental research and practical applications.

Recreating textbook models from quantum physics is far from a purely academic pursuit. It has practical implications too, as quantum technologies hold the promise of revolutionizing communication, computation, and measurement. Yet, the inherent fragility of quantum states and their elusive nature pose significant challenges to real-world applications. Through their innovative use of nanographene “quantum Lego,” Empa researchers hope to deepen our understanding of quantum effects, ultimately paving the way toward robust, usable quantum technologies.

Further information
Prof. Dr. Roman Fasel
Empa, nanotech@surfaces
Phone +41 58 765 43 48
roman.fasel@empa.ch

Dr. Pascal Ruffieux
Empa, nanotech@surfaces
Phone +41 58 765 46 93
pascal.ruffieux@empa.ch

Editor / Media Contact
Anna Ettlin
Empa, Communications
Phone +41 58 765 47 33
redaktion@empa.ch