Researchers at the Max Planck Institute for the Science of Light have created a method to examine molecules on surfaces with high spectroscopic accuracy, achieving the fundamental quantum limit. Published in Science, the work opens possibilities for studying molecule-surface interactions and molecular quantum technologies.
Many quantum technologies depend on nanoscale objects like atoms or molecules that interact with light. These emitters enable single-photon generation, quantum information storage and entanglement distribution for communication and computation.
To study individual emitters, they must remain stable for extended periods. This is typically done by trapping them in vacuum or embedding them in bulk materials. Emitters on surfaces could allow direct manipulation, such as with sharp tips used in scanning tunneling or atomic force microscopy.
Until now, controlling surface-bound emitters while maintaining their quantum properties has been difficult. Surfaces often collect contaminants, producing unstable conditions that degrade performance. The MPL team developed a solution to this problem.
They used an organic crystal that evaporates slowly at room temperature. Placed in a cryostat under vacuum, the top layers sublimate and remove contaminants. The crystal is then cooled to a few degrees above absolute zero. Molecules are deposited on the surface using a microfabricated oven.
Coherence times measure how long emitters retain quantum properties and cannot exceed the Fourier limit set by energy transfer to the surroundings. In noisy environments, these times are much shorter.
On the clean crystal surface, the molecules reached the Fourier limit, showing stable and quiet conditions. This is the first time the limit has been achieved on a surface.
The team also found that the surface orients the molecules, shifts their energies and may alter their shape or vibrations.
Future work will combine the technique with atomic force and scanning tunneling microscopy for nanoscale control of individual emitters, providing new insights into surface properties and quantum states of matter.
