Synthesising quantum states of sound and listening to what they tell us about the universe

The Schrodinger-cat thought experiment infamously highlights how bizarre quantum mechanics can be and just how little we know about the fuzzy boundary between the quantum and classical aspects of our world. Using quantum technologies and our now exquisite ability to control the quantum aspects of light, this project will illuminate and examine this boundary by creating quantum states of high-frequency sound waves in a tiny crystal cooled to near absolute zero in temperature. These quantum sound waves will comprise trillions of atoms--a mass-scale that is truly gigantic from the perspective of the quantum realm, which usually only contains a very small number of particles or atoms, but is just on the edge of our everyday world, as that mass would make up just a small fraction of a single feline hair. Generating and studying quantum behaviour at this mass-scale will act as a new and powerful lens through which we can examine the very foundations of physics and shed much needed light on: Why do we not see quantum behaviour in our everyday world? Why are quantum states so fragile? And, does gravity even play a role at this mysterious boundary?