Quantum superposition with a sapphire crystal

In 2023, researchers at ETH Zurich led by Yiwen Chu placed a 16-microgram sapphire crystal into a quantum superposition, a state where an object exists in multiple states at once. This experiment, published in the journal Science, involved a sapphire resonator with around 100 million billion atoms, placed in a superposition of two opposite vibrational states.

How the superposition was achieved

The device used a superconducting qubit connected to the resonator through a thin piezoelectric layer, which transmitted the quantum superposition to the crystal. This represents a major advancement, as the sapphire crystal's mass is over 100,000 billion times greater than the largest previously observed quantum superposition in molecules.

The significance of the experiment

The experiment allows researchers like Matteo Fadel to test the Diósi-Penrose gravitational collapse model, which suggests gravity might explain why quantum superpositions disappear at larger scales. In this setup, the sapphire crystal vibrates in two opposite directions at the same time, replacing the hypothetical "alive and dead" cat from Schrödinger's thought experiment.

Technical challenges and collaboration

The chips used in the experiment were manufactured in cleanrooms at ETH Zurich and IBM Zurich, where even a single speck of dust can destroy months of work. This highlights the need for both theoretical insight and technical precision. The team had to ensure the separation between the two vibrational states was large enough to be distinguishable from background noise.

Future research and implications

This breakthrough opens new avenues for studying the boundary between quantum and classical physics. The coming years may determine if this approach helps resolve debates about where quantum effects end and classical reality begins.