In a remarkable achievement that answers a century-old challenge in physics, scientists have successfully demonstrated the first-ever diffraction of atomic matter waves through a crystalline material. This accomplishment by researchers at the German Aerospace Center and the University of Vienna, opens new possibilities for quantum sensors and our understanding of atomic behavior [1].
The Power of Atomic Diffraction
To understand the significance of this achievement, we need to step back to the foundations of quantum mechanics. In 1923, Louis de Broglie proposed that matter, like light, exhibits wave-like properties. This wave nature of particles was quickly demonstrated for electrons, atoms, and molecules through diffraction experiments. Just as light waves can bend and spread out when passing through a grating, matter waves show similar behavior.
Diffraction has since become a cornerstone of modern physics, leading to revolutionary technologies like electron microscopes and atomic interferometers. These tools have helped us measure fundamental constants, search for new physics beyond our current understanding, and create increasingly precise sensors.
However, until now, one particular challenge remained unsolved: no one had successfully demonstrated atomic diffraction through a crystal. While crystal-based diffraction had been achieved with electrons and in reflection for atoms -were atoms are bounced off a etched grated surface- transmitting atoms through a crystal while maintaining their wave-like properties seemed nearly impossible due to the strong interactions between the passing atoms and the crystal structure.
The Breakthrough Approach
The research team tackled this challenge by using single-layer graphene – a one-atom-thick sheet of carbon atoms arranged in a honeycomb pattern – as their crystalline material. They fired beams of helium and hydrogen atoms at high energies (between 390 and 1600 electron volts) through the graphene sheet and observed the resulting diffraction patterns.
What makes this achievement particularly remarkable is that it works at all. When atoms pass through the graphene, they come within mere angstroms (one ten-billionth of a meter) of the carbon atoms making up the crystal structure. At these tiny distances, the atomic orbitals of the passing atoms significantly overlap with those of the graphene. Conventional wisdom suggested this would destroy any quantum coherence and make diffraction impossible.
The secret to succeed lies in the speed of the atoms. By using high-energy atoms, the researchers ensured that each atom spent only an incredibly brief time – measured in femtoseconds (quadrillionths of a second) – interacting with the graphene. This ultra-short interaction time helps preserve the quantum coherence necessary for diffraction to occur.
Record-Breaking Performance
The results are impressive by any measure. The team observed diffraction patterns showing that atoms scattered by up to eight times the crystal’s fundamental momentum transfer unit.
To put this in perspective, achieving the same momentum transfer using traditional laser-based techniques with rubidium atoms would require scattering more than 50,000 photons. This makes their system the beam splitter with the largest known momentum transfer for atoms in transmission.
The graphene crystal proved remarkably durable as well. Despite some samples being bombarded with atomic beams for more than 100 hours, they showed no degradation in performance. This durability is crucial for practical applications.
Future Implications
This breakthrough opens several exciting avenues for future research and applications. The ability to diffract atoms through crystals at high energies provides a new tool for studying quantum decoherence – the process by which quantum systems lose their wave-like properties through interaction with their environment. This could help us better understand the boundary between quantum and classical physics.
The technique might also lead to new types of quantum sensors. Fast atoms have certain advantages over cold atoms for detecting gravitational waves, and this new diffraction method could enable novel multi-dimensional interferometers. Such devices could find applications in everything from fundamental physics experiments to practical navigation and surveying tools.
The research team suggests that exploring different crystal materials and energy ranges could yield additional insights. Using single crystals instead of polycrystalline samples would allow scientists to separate coherent and incoherent contributions to the diffraction patterns, providing even more detailed information about the atom-crystal interactions.
Unified Science in Perspective
This achievement can be seen as the atomic counterpart to G.P. Thomson’s groundbreaking experiments with electron diffraction through thin films in the 1920s. Thomson’s work helped establish the wave nature of electrons and earned him the 1937 Nobel Prize in Physics. Now, nearly a century later, scientists have finally achieved the same feat with atoms, marking another milestone in our exploration of quantum mechanics.
The success of this experiment demonstrates that even in well-established fields like atomic physics, fundamental new discoveries remain possible. It reminds us that persistence in tackling seemingly impossible challenges can lead to breakthrough moments that expand our understanding of the natural world and open new technological possibilities. The ability to diffract atoms through crystals provides not just a new tool for scientific investigation, but also a reminder that there are still fundamental discoveries waiting to be made in the quantum realm.
References
[1] Carina Kanitz et al. Diffraction of atomic matter waves through a 2D crystal (Dec 3, 2024) . https://arxiv.org/pdf/2412.02360
