Researchers Coax Levitating Glass Bead Into the Quantum World

Studying the quantum state of the universe is a challenging endeavor in part because objects only have detectable quantum properties on the smallest of scales. The larger something is, the harder it is to get it into a well-defined quantum state unobscured by environmental effects. A team of US-Austrian researchers has developed a new technique that could make quantum mechanics easier to study thanks to a floating silica bead

The basic problem when studying quantum states is that larger objects have more interaction with the environment, and that masks quantum properties. Pushing matter into a quantum state usually requires complex resonators that control atoms with specific wavelengths of light. These systems only work at extremely low temperatures verging on absolute zero, which prevents outside energy from affecting the particles. With the right controls, scientists can coax clouds of atoms to form exotic materials like Bose-Einstein condensates. 

It is therefore rather remarkable that the team from MIT, the University of Vienna, and the Austrian Academy of Sciences managed to coax a solid object into the quantum regime. The researchers placed a small silica bead about 200 nanometers across in a vacuum chamber and then used a laser (sometimes called optical tweezers) to suspend it in the air. With gas, laser cooling via atomic transition is a well-understood method of removing energy to get atoms into a quantum ground state. With the solid levitating bead, the team had to use a new experimental method called cavity cooling by coherent scattering.

With millions of atoms packed together, the silica bead is observationally free of quantum properties under normal conditions. The cavity cooling method relies on a test chamber with dimensions similar to a specific wavelength of light. That limits the wavelengths that can exist within the chamber.

Over time, the bead loses energy to environmental photons, which have more energy than the optical tweezers inside the cavity. Eventually, the bead stops vibrating, and the center reaches around 0.00001 degrees Celsius away from absolute zero, allowing it to develop observable quantum properties. At this point, the surface of the bead is actually quite hot at roughly 572 degrees Fahrenheit (300 degrees Celsius), and the rest of the experiment is room temperature. 

The team says this setup allows the glass bead to enter a quantum ground state 70 percent of the time. It may be possible to reach even higher success rates with improved vacuum hardware. They also discuss cooling the hardware to improve efficacy. Further study of solid quantum state objects could yield fascinating results, but we’re just at the dawn of this new era.

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