EPFL physicists have found a way to measure the time involved in quantum events and found it depends on the symmetry of the material. “The concept of time has troubled philosophers and physicists for thousands of years, and the advent of quantum mechanics has not simplified the problem,” says Professor Hugo Dil, a physicist at EPFL. “The central problem is the general role of time in quantum mechanics, and especially the timescale associated with a quantum transition.”

Quantum events, like tunneling, or an electron changing its state by absorbing a photon, happen at mind-bending speeds. Some take only a few tenths of attoseconds (10^-18 seconds), which is so short that light would not even cross the width of a small virus. But measuring time intervals this small is notoriously difficult, also because any external timing tool can distort the very thing we want to observe.

“Although the 2023 Nobel prize in physics shows we can access such short times, the use of such an external time scale risks inducing artifacts,” says Dil. “This challenge can be resolved by using quantum interference methods, based on the link between accumulated phase and time.”