Researchers at the Max Planck Institute for the Science of Light have achieved a significant advancement in quantum physics by successfully studying individual molecules attached to surfaces with unprecedented precision. The team demonstrated that molecules can reach the Fourier limit, the theoretical maximum for quantum coherence, marking the first time this fundamental boundary has been achieved with molecules on a surface. The findings appear in Science and may enable new applications in quantum computing and secure communication systems.
Quantum emitters—individual atoms and molecules that interact with light—are essential components for emerging quantum technologies, as they can produce single photons and store quantum information. Researchers have traditionally confined these systems in vacuums or within solid materials to maintain stability. Placing quantum emitters directly on surfaces would offer advantages, such as the ability to manipulate molecules using atomic-scale probes through techniques like scanning tunneling microscopy and atomic force microscopy. However, environmental contaminants accumulating on surfaces have historically prevented researchers from preserving the quantum optical properties necessary for these applications.
The research team, led by Prof. Vahid Sandoghdar, developed an innovative cleaning approach exploiting a natural property of organic crystals. At room temperature, crystal surfaces gradually evaporate through sublimation, a process in which solids transform directly into gas. By placing a crystal in a vacuum chamber at extremely low temperatures and allowing its uppermost layers to slowly evaporate, contaminants were carried away, yielding an exceptionally clean surface. After cooling the crystal to a few degrees above absolute zero to halt further sublimation, the researchers deposited molecules onto the pristine surface.
With this stable environment established, the team measured the coherence times of the molecules—the duration they maintain quantum properties. The scientists found that molecules consistently achieved the Fourier limit, a fundamental physical boundary determined by the time required for quantum emitters to release energy into their surroundings. This represented the first demonstration of molecules on a surface reaching this theoretical maximum coherence time. The experiments also revealed that surface interactions influence molecular alignment, energy levels, and potentially molecular shape and vibrations.
The researchers plan to integrate their ultra-clean surface technique with advanced microscopy methods to achieve nanometer-scale control over individual quantum emitters. Such capabilities could illuminate previously unexplored details about molecule-surface interactions and facilitate the engineering of novel quantum states and advanced molecular quantum technologies.
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