They began with a a tiny mechanical paddle, or ‘quantum drum’, around 30 micrometres long that vibrates when set in motion at a particular range of frequencies. Next they connected the paddle to a superconducting electrical circuit that obeyed the laws of quantum mechanics. They then cooled the system down to temperatures below one-tenth of a kelvin.
At this temperature, the paddle slipped into its quantum mechanical ground state. Using the quantum circuit, Cleland and his team verified that the paddle had no vibrational energy whatsoever. They then used the circuit to give the paddle a push and saw it wiggle at a very specific energy.
Next, the researchers put the quantum circuit into a superposition of ‘push’ and ‘don’t push’, and connected it to the paddle. Through a series of careful measurements, they were able to show that the paddle was both vibrating and not vibrating simultaneously.
“It’s wonderful,” says Hailin Wang, a physicist at the University of Oregon in Eugene who has been working on a rival technique for putting an oscillator into the ground state. The work shows that the laws of quantum mechanics hold up as expected on a large scale. “It’s good for physics for sure,” Wang says.