Physicists from the University of Kaiserslautern-Landau, led by Professor Dr. Herwig Ott, have achieved a groundbreaking feat by directly observing pure trilobite Rydberg molecules. What makes these molecules intriguing is their unique shape reminiscent of trilobite fossils, coupled with the distinction of having the largest electric dipole moments among all known molecules.
Employing a specialized apparatus capable of preparing these delicate molecules at ultralow temperatures, the researchers delved into the chemical binding mechanisms, setting them apart from conventional bonds. The findings were recently published in the journal Nature Communications.
In their experiment, the team utilized a cloud of rubidium atoms cooled to a mere 100 microkelvin in an ultra-high vacuum—just 0.0001 degrees above absolute zero. By employing lasers, they excited some atoms into a Rydberg state, causing the outermost electron to orbit far from the atomic body. Professor Herwig Ott elaborates, “The orbital radius of the electron can be more than one micrometer, making the electron cloud larger than a small bacterium.” These highly excited atoms, also found in interstellar space, exhibit remarkable chemical reactivity.
When a ground state atom is situated within this giant Rydberg atom, a trilobite molecule is formed, bound by a distinctive quantum mechanical scattering mechanism. Max Althön, the study’s first author, explains, “Imagine the electron rapidly orbiting around the nucleus. On each round trip, it collides with the ground state atom. In contrast to our intuition, quantum mechanics teaches us that these collisions lead to an effective attraction between the electron and the ground state atom.”
The resulting molecules boast fascinating properties: the wave nature of the electron induces multiple collisions, creating an interference pattern resembling a trilobite. Additionally, the molecule’s bond length matches the Rydberg orbit, surpassing that of any other diatomic molecule. The permanent electric dipole moment is remarkably large, exceeding 1,700 Debye.
To observe these molecules, the scientists devised a dedicated vacuum apparatus enabling the preparation of ultracold atoms through laser cooling and subsequent spectroscopic detection of the molecules. These findings contribute to understanding fundamental binding mechanisms crucial for the burgeoning field of quantum computing applications utilizing Rydberg atoms. The researchers’ discovery adds depth to the comprehension of Rydberg systems, showcasing their exotic and practical aspects simultaneously.