Scientists at the Max Planck Institute for the Science of Light (MPL) have achieved a breakthrough in quantum physics, developing a way to study individual molecules on a surface with extraordinary precision. For the first time, researchers have demonstrated that molecules attached to a surface can reach the ultimate quantum limit of optical coherence, overcoming a major obstacle that has long restricted molecular quantum research. The findings, published in Science, could open new possibilities for investigating how molecules interact with surfaces and developing advanced quantum technologies.
Why Surfaces Have Been a Major Obstacle in Quantum Physics Many emerging quantum technologies depend on extremely small objects, such as individual atoms and molecules, that interact with light. Known as quantum emitters, these tiny systems can produce single particles of light called photons, store quantum information, and help establish quantum connections between distant systems. These capabilities are important for future applications in quantum computing and secure quantum communication.
To study a single quantum emitter, scientists must keep it stable and confined to one location for extended periods. Traditionally, researchers have accomplished this by trapping atoms or molecules in a vacuum or embedding them inside solid materials. Placing quantum emitters directly on a surface, however, offers an intriguing advantage.
Scientists could potentially manipulate individual molecules by "touching them" with an extremely sharp probe. Techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM) already use tips with atomic precision to investigate matter at incredibly small scales. The difficulty is that surfaces are rarely as clean and stable as quantum experiments require.
Contaminants from the surrounding environment can accumulate on them, creating disturbances that interfere with the delicate quantum behavior of nearby atoms and molecules. Until now, researchers had struggled to preserve the quantum optical properties of individual emitters attached to surfaces. Scientists in MPL's Nano-Optics Division have now found a way around this problem.
A Clever Crystal Cleaning Method Solves the Problem The research team, led by Prof. Vahid Sandoghdar, director at MPL and head of the "Nano-Optics" Division, developed an unusual cleaning method that takes advantage of a natural property of organic crystals. At room temperature, the crystal material gradually evaporates through a process known as sublimation, in which a solid transforms directly into a gas without first becoming a liquid.
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