Scientists have achieved a major breakthrough in quantum physics by showing that individual molecules attached to a surface can preserve their delicate quantum properties at the ultimate physical limit. The discovery solves a long-standing challenge in molecular quantum research and could open new possibilities for controlling matter at the smallest scales.
The research was conducted by scientists at the Max Planck Institute for the Science of Light (MPL). Their work, published in the journal Science in 2026, demonstrates that molecules placed on an exceptionally clean crystal surface can maintain their optical coherence for as long as fundamental physics allows.
This achievement could help researchers develop more precise quantum devices, improve their understanding of molecular behavior, and explore new ways to control individual molecules using advanced microscopy techniques.
Why Are Scientists Interested in Quantum Molecules?
Quantum physics describes how matter and energy behave at extremely small scales, including the world of atoms, electrons, and individual molecules. At this level, particles can display unusual properties that are very different from the behavior of everyday objects.
One important feature is quantum coherence. In simple terms, coherence describes how well a quantum system maintains the precise relationships between its possible quantum states. These relationships are essential for many quantum effects and applications.
Scientists are particularly interested in quantum emitters, which are tiny systems that interact with light and can release individual particles of light called photons.
These systems could play important roles in future technologies, including quantum computing, secure quantum communication, and devices designed to connect distant quantum systems.
However, studying and controlling individual quantum emitters is not easy. Their quantum properties are extremely sensitive to their surroundings. Even small environmental disturbances can interfere with their behavior and cause them to lose coherence.
To protect these delicate systems, researchers have traditionally trapped atoms or molecules in carefully controlled vacuum environments or embedded them inside solid materials.
But placing quantum emitters directly on a surface offers a different approach. It could allow scientists to examine and manipulate individual molecules with extraordinary precision.
The challenge has been finding a surface clean and stable enough to preserve their quantum properties.
Why Surfaces Have Been a Major Challenge
Surfaces are essential in many scientific experiments because they provide a place to position, observe, and manipulate individual atoms and molecules.
Advanced tools such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM) allow researchers to investigate matter at incredibly small scales.
STM can examine surfaces by measuring electrical current between a sharp tip and a sample. AFM uses a tiny probe to detect forces between the tip and the material being studied.
Both techniques can provide information about individual atoms and molecules, and they offer the potential for highly precise control.
However, a major problem remains: surfaces are rarely perfectly clean.
Unwanted particles, chemical impurities, and microscopic defects can disturb nearby molecules. These interactions can change molecular energy levels and interfere with the delicate quantum behavior scientists want to study.
Even when a molecule is carefully placed on a surface, its surroundings can cause its quantum coherence to disappear much faster than expected.
For years, this environmental interference has made it difficult to achieve the highest possible optical coherence in molecules attached to solid surfaces.
The research team at MPL developed a method designed to overcome this obstacle.
An Unusual Cleaning Technique Inspired by Nature
The breakthrough came from using a natural property of organic crystals: sublimation.
Sublimation occurs when a solid changes directly into a gas without passing through the liquid state. Familiar examples include dry ice and certain substances that gradually disappear when exposed to suitable conditions.
The researchers used this process to clean a crystal surface under carefully controlled conditions.
Led by Professor Vahid Sandoghdar, director of MPL's Nano-Optics Division, the team placed a small organic crystal inside a vacuum chamber equipped with a cryostat, a device used to achieve and maintain extremely low temperatures.
At suitable temperatures, the crystal's outermost layers gradually sublimated. As material left the surface, it carried away unwanted contaminants, helping expose a cleaner layer underneath.
The researchers then cooled the crystal to just a few kelvin above absolute zero, the theoretical lower limit of temperature. At these extremely low temperatures, further sublimation was effectively halted, helping preserve the clean surface.
Next, the team used a specially designed miniature oven to evaporate individual molecules onto the cold crystal. The molecules settled onto the carefully prepared surface, creating a stable environment for quantum experiments.
This combination of crystal cleaning, vacuum conditions, and extreme cooling was crucial to the achievement.
Molecules Reach the Fundamental Limit of Quantum Coherence
After preparing the surface, the scientists investigated how well the deposited molecules could maintain their optical coherence.
One important measure of a quantum emitter's performance is its coherence time. This indicates how long it can preserve the quantum relationships needed for its behavior to remain coherent.
Generally, longer coherence times are valuable because they allow scientists to study quantum systems and interact with them more precisely.
However, even in an ideal environment, coherence has a fundamental limit associated with the finite lifetime of an excited quantum state.
This relationship is connected to the Fourier limit, which links the duration of a quantum transition to the natural width of its optical spectrum.
When a quantum emitter is disturbed by its environment, its spectral line can become broader and its coherence can decay more rapidly than this fundamental limit would suggest.
In other words, environmental noise can prevent a molecule from displaying its best possible quantum performance.
The MPL researchers found that their surface-bound molecules could reach the Fourier limit.
This means that the molecules' optical transitions were limited by their intrinsic physical properties rather than being significantly degraded by environmental disturbances.
The result demonstrates that an individual molecule attached to a solid surface can maintain optical coherence at the fundamental limit set by its transition lifetime.
According to the researchers, this is the first demonstration of a Fourier-limited optical transition in a single molecule adsorbed on a surface.
It represents an important step toward studying and controlling quantum systems without needing to isolate every emitter completely from a solid material.
What Did Scientists Discover About the Molecules?
The experiments revealed more than just exceptionally stable quantum behavior.
The researchers also investigated how the crystal surface influenced the molecules resting on it.
They found that interactions between the molecules and the surface could influence their orientation and modify their energy levels.
The results also suggested that the surface might affect molecular shapes or vibrational behavior.
These findings are important because a molecule does not exist independently of its surroundings when attached to a solid. Its interaction with nearby atoms can influence how it moves, absorbs light, and transitions between quantum states.
By studying these effects under exceptionally controlled conditions, scientists may be able to understand molecular interactions in greater detail.
This knowledge could eventually help researchers design systems in which surface interactions are not simply unavoidable disturbances but useful tools for controlling quantum behavior.
How Could This Breakthrough Change Future Technology?
The discovery is an important step toward developing more controllable molecular quantum systems, although practical applications will require further research.
One promising direction is quantum information technology. Quantum devices rely on delicate quantum states to process or transmit information. More stable quantum emitters could help scientists investigate ways to generate and control photons for future quantum communication systems.
Another possibility is advanced molecular sensing. Because individual molecules respond to their local surroundings, highly precise measurements of their optical properties could help researchers study extremely small changes in their environment.
The technique could also improve fundamental research into how molecules interact with solid materials. This knowledge is relevant to areas such as surface chemistry, molecular electronics, and nanoscale physics.
Perhaps most importantly, the researchers want to combine their technique with AFM and STM.
Professor Sandoghdar explained that future work will focus on achieving local, nanometer-scale control over individual quantum emitters.
A nanometer is one-billionth of a meter. At this scale, researchers could potentially investigate and manipulate individual molecules with unprecedented precision.
Combining ultra-clean surfaces with these microscopy tools could allow scientists to study how a molecule's position, orientation, and immediate surroundings affect its quantum properties.
Such control could help researchers explore new quantum states and develop experimental platforms for future molecular quantum technologies.
A New Way to Explore the Quantum World
The achievement marks an important advance in scientists' ability to study individual molecules directly on solid surfaces.
By using sublimation to remove contaminants and extreme cooling to preserve surface cleanliness, the MPL team overcame a problem that has limited molecular quantum experiments for years.
Most importantly, the researchers demonstrated that a molecule attached to a surface can reach the fundamental Fourier limit of optical coherence.
The discovery does not mean that practical quantum computers or communication devices based on this method are ready for use. However, it provides scientists with a powerful new platform for investigating and controlling individual quantum systems.
As researchers continue to combine this approach with advanced microscopy, they may gain access to details of molecular behavior that were previously difficult to observe.
Sometimes, progress in quantum technology depends not on building something bigger, but on making the smallest possible systems stable enough to reveal their true potential.
Reference
Masoud Mirzaei, Alexey Shkarin, Burak Gurlek, Johannes Zirkelbach, Ashley J. Shin, Irena Deperasińska, Boleslaw Kozankiewicz, Tobias Utikal, Stephan Götzinger, and Vahid Sandoghdar. “Nano–electron volt Fourier-limited transition of a single surface-adsorbed molecule.” Science, 2026, 392 (6805): 1384. DOI: 10.1126/science.aeg5014.
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