What if we could control quantum interference in time, where electrons created at different moments overlap and interfere? In this study, published in Physical Review Letters, a team of researchers developed a novel technique—chirped laser-assisted dynamic interference—to manipulate temporal quantum interference during photoionization.
By using extreme-ultraviolet pulses with time-varying central frequency, in combination with intense infrared laser fields, they guided electron motion with unprecedented precision.
Careful tuning of the pulse timing and intensity enabled the researchers to control the photoemission process such that electrons emitted at different times reached the same final energy, allowing their quantum trajectories to interfere coherently. This interference gave rise to well-defined fringe patterns in the photoelectron spectra, revealing key information about the underlying ultrafast physics.
These findings, supported by advanced simulations and experiments at ELI ALPS, represent the first clear experimental observation of this elusive phenomenon, long theorized but previously obscured by competing multiphoton interference effects.
ELI ALPS researchers played a key role in overcoming these challenges in the experiment by realizing complex requirements necessary to this discovery. Specifically, based on a theoretical proposal by co-authors at Lund University, they utilized two carefully tailored and optically synchronized light pulses of very different – extreme ultraviolet and infrared – colours, with which it was possible to isolate and handle atomic effects separately. The measurement, conducted using the HR Condensed beamline, showcases the unique experimental capabilities of ELI ALPS in pushing the boundaries of ultrafast science.
The study is the result of a close collaboration between researchers at Politecnico di Milano, Lund University, IFN-CNR, ETH Zürich and ELI ALPS.
Offering deeper insight into how matter responds to intense laser fields at the quantum level, this breakthrough gives researchers a powerful new tool to manipulate the behaviour of electrons on attosecond timescales (a billionth of a billionth of a second), unlocking new possibilities for quantum technologies and ultrafast electronics.
Photos: Gábor Balázs