A laser beam hits an atom, and an electron is knocked loose. It accelerates, returns, and, crashing into the atom, emits a flash of light — a harmonic. If there are two light beams and they are crossed like an intersection, the electron can choose different routes. In the new experiment, the two beams had comparable strength and were directed at right angles. Then the electron paths become two-dimensional, and their interference becomes visible.
By measuring the brightness of harmonics as the phase shift between the beams was varied, the scientists saw: odd harmonics change in one smooth way, while even harmonics change in two different ways. Calculations using the strong-field approximation and saddle-point method showed that the electron response inherits the dynamical symmetry of the crossed field. This is a new type of two-dimensional quantum path interference.
This approach raises the dimensionality of quantum paths involved in interference and promises a new spectroscopy of attosecond electron dynamics — motion lasting billionths of a billionth of a second.
An attosecond is so short that in one attosecond, light travels a distance smaller than the size of an atom.
In the series 'The Expanse', ships jump through rings using quantum tunnels; here, the electron also 'jumps' along multiple paths simultaneously, but without any science fiction.