Researchers Break Record for Quantum Mechanics with Heavy Nanoparticles

A team of researchers from Austria and Germany has significantly advanced the understanding of quantum mechanics by demonstrating that large metal nanoparticles, weighing over 170,000 atomic mass units, continue to exhibit quantum behavior. This breakthrough, detailed in the journal Nature, challenges the boundary between quantum and classical mechanics, raising questions about the fundamental nature of reality.

The study, led by Sebastian Pedalino, a PhD student at the University of Vienna, involved experiments that showcased the quantum properties of clusters of sodium atoms at extremely low temperatures. By utilizing a double-slit experiment, the researchers illustrated that these nanoparticles, which consist of thousands of atoms, remain governed by the principles of quantum mechanics even at macroscopic scales.

In the experiment, the team created clusters of sodium atoms in a helium-argon mixture at 77 K within an ultrahigh vacuum. Each cluster contained between 5,000 and 10,000 atoms, traveling at speeds around 160 m/s. This setup allowed the researchers to calculate the de Broglie wavelengths of the clusters, which ranged from 10‒22 femtometres.

To observe the matter-wave interference, the researchers employed an interferometer featuring three diffraction gratings designed with deep ultraviolet laser beams in a Talbot–Lau configuration. The first grating directed the clusters through narrow gaps, causing their wave function to expand. This wave function was then modulated by the second grating, resulting in observable interference patterns at the third grating. The outcome indicated that the clusters did not occupy a fixed position but instead existed in a superposition of locations, embodying what is known as a Schrödinger cat state. This term references the famous thought experiment by physicist Erwin Schrödinger, in which a cat in a sealed box is simultaneously alive and dead.

The researchers quantified their findings by calculating a measure known as macroscopicity, which combines the coherence time, mass of the object, and the degree of separation between states. Their results achieved a macroscopicity value of 15.5, an order of magnitude higher than previously recorded measurements in this field.

Markus Arndt, one of the lead researchers, emphasized the importance of this finding. He stated, “The motivation is simply that we do not yet know if quantum mechanics is the ultimate theory or if it requires any modification at some mass limit.” While some speculative theories suggest potential modifications to quantum mechanics, Arndt insists on the necessity of remaining open to experimental outcomes.

The sensitivity of their experimental setup to small forces may have broader implications. Arndt believes that this capability could be harnessed to explore material properties and possibly search for new particles in future experiments. He expressed both amazement and intrigue at the ability of these mesoscopic objects to exist in a delocalized state, stating, “The interpretation of this phenomenon, the duality between this delocalization and the apparently local nature in the act of measurement, is still an open conundrum.”

Looking ahead, the team plans to enhance their research by extending investigations to larger mass objects, increasing coherence times, and exploring various materials, including nanobiological substances and different metals. Arndt noted, “We still have a lot of work to do on sources, beam splitters, detectors, vibration isolation, and cooling. This is a big experimental adventure for us.”

This research not only pushes the boundaries of our understanding of quantum mechanics but also opens new avenues for scientific exploration in the field. The implications of such findings may reshape our comprehension of the quantum-classical divide, potentially leading to new technologies and insights into the fundamental laws of nature.