The researchers observed the atoms under a microscope by illuminating them with a separate imaging laser. A light microscope can’t see individual atoms, but the imaging laser causes them to fluoresce, and the microscope captured the flashes of light. When the imaging laser was off, or turned on only dimly, the atoms tunneled freely. But as the imaging beam was made brighter and measurements made more frequently, the tunneling reduced dramatically.“This gives us an unprecedented tool to control a quantum system, perhaps even atom by atom,[…]Using this tuning, we’ve also been able to demonstrate an effect called ‘emergent classicality’ in this quantum system.” Quantum effects fade, and atoms begin to behave as expected under classical physics.

Source: ‘Zeno effect’ verified: Atoms won’t move while you watch | Cornell Chronicle

The famous Heisenberg uncertainty principle says that position and velocity of a particle are related and cannot be simultaneously measured precisely.