PRL First detection of quantum entanglement waves!

Triplons are tricky little particles. They are extremely difficult to observe in experiments. Even so, researchers usually test them on macroscopic materials, with measurements expressed as an average over the entire sample.

Uniquely, says Robert Drost, first author of a paper published in Physical Review Letters and a researcher at the National Academy of Sciences, this is where designer quantum materials have a unique advantage. These designer quantum materials could allow researchers to create phenomena not found in natural compounds and ultimately achieve exotic quantum excitations.

"Real-Space Imaging of Triplon Excitations in Engineered Quantum Magnets"

"These materials are very complex. They can provide very exciting physics, but the most exotic materials are also difficult to find and study." Professor Peter Liljeroth, head of the Atomic Scale Physics research group at Aalto University, said, "We are therefore trying a different approach to building artificial materials using individual components."

Quantum materials are governed by interactions between electrons at the microscopic level. These electron correlations lead to unusual phenomena: such as high-temperature superconductivity or complex magnetic states, and the quantum correlations give rise to new electronic states.

In the case of two electrons, there are two entangled states, a singlet and a triplet; supplying energy to an electronic system can excite it from a singlet to a triplet. In some cases, this excitation propagates through the material as an entangled wave called a triple state (triplon). Such excitations do not exist in conventional magnetic materials, so measuring them has been a challenge in the field of quantum materials.

In this new study, the team used small organic molecules to create an artificial quantum material with unusual magnetic properties. Each cobalt phthalocyanine molecule used in the experiment contains two frontier electrons.

Drost shared, "Using very simple molecular building blocks, we were able to design and probe this complex quantum magnet in a way that has never been possible before, revealing phenomena that are not present in its standalone parts. While magnetic excitation in isolated atoms has long been observed using scanning tunneling spectroscopy, this has never been accomplished using propagating triplets."

"We use these molecules to bind electrons together, fitting them into a small space and forcing them to interact. Looking at such a molecule from the outside, we see the joint physics of the two electrons. Because our basic building blocks now contain two electrons, instead of one, we see a very different kind of physics."

The team first monitored the magnetic excitation of a single cobalt phthalocyanine molecule, and then monitored the magnetic excitation of larger structures such as molecular chains and molecular islands. By starting with very simple phenomena and gradually increasing the complexity, the researchers hope to understand emergent behavior in quantum materials. In the current study, the team could demonstrate that single-triplet excitations of its building blocks can traverse molecular networks as exotic magnetic quasiparticles called triplets.

Magnetic excitation of a cobalt phthalocyanine molecule in which entangled electrons propagate into triplets

Triple baryon excitation in a molecular spin chain

A complete data set of experimental analyses.

Spin modeling results

"Our study shows that we can generate exotic quantum magnetic excitations in man-made materials." Assistant Professor Jose Lado, one of the study's co-authors and head of the related quantum materials research group at Aalto University, said, "This strategy shows that we can rationally design materials platforms that open up new possibilities for quantum technology."

In the future, the research group plans to extend their approach to more complex building blocks to design other exotic magnetic excitations and orderings in quantum materials. Rational design from simple components will not only help to understand the complex physics of the electronic systems involved, but also establish new platforms for designing quantum materials.

Reference links:

[1] https://www.techexplorist.com/quantum-entanglement-wave-detected-first-time/67711/

[2] https://phys.org/news/2023-08-group-quantum-entanglement-real-space.html