Exploring the Quantum World with Ultracold Atoms

By cooling atoms to temperatures just a tiny fraction of a degree above absolute zero, we can slow their motion enough to observe their strange quantum behavior directly. At these nanokelvin temperatures, atoms no longer behave like tiny billiard balls—they start to act like waves.

According to quantum physics, every particle has a de Broglie wavelength, which depends on its mass and velocity. When atoms are cold enough, their de Broglie waves grow and begin to overlap with each other. This overlap creates a remarkable state of matter known as a Bose-Einstein condensate, where many atoms behave as one unified quantum object.

In a recent breakthrough, scientists used a single-atom microscope to directly observe these de Broglie wavelengths—something that has been observed only for atoms in a beam, but not in-situ for a thermal cloud. It’s a vivid confirmation that individual atoms can indeed act like waves.

The wave-like nature of particles isn’t limited to atoms. The double slit experiment, first done with light, showed that waves can interfere to create patterns of bright and dark stripes. Later, similar experiments with atoms showed that matter itself can behave like a wave. One of the key discoveries from these experiments is that if you try to find out which slit the particle went through, the interference pattern starts to disappear—highlighting the famous wave-particle duality of quantum mechanics.

In our new experiment, we’ve taken this idea even further. We performed an atomic version of the double slit experiment, not with physical slits, but with two individual atoms that scatter light one photon at a time. Even more impressively, these atoms weren’t confined in a trap—they were freely floating in space, prepared in delicate quantum wave packets limited only by the Heisenberg uncertainty principle. This allowed us to explore fundamental questions about how light and matter interact at the most basic quantum level.