Quantum superposition, big enough to see!
After confirming that the paddle was in its quantum ground state (no vibrational energy), they put the superconducting circuit into a superposition of on- and off states, and directly measured that the paddle was in the corresponding superposition of vibrating and not vibrating.
In the words of J.B.S. Haldane, "Life is not only queerer than we imagine, it is queerer than we can imagine."
Update #1: Science News also has a report on this result, with some slightly different details. The paper itself is a pay-per-view Nature article.
Update #2: Science magazine now also has a report on this result, with a better and more detailed explanation of the superconducting phase circuit.