Abstract
We successfully observed electronic oscillation (dipole oscillation) with attosecond (as: 10‒18 of a
second) periodicity using gallium nitride (GaN) wide-bandgap semiconductor. A few-cycle near-infrared
pulse induces the ultrafast electric interband polarization. The Dipole oscillation with 860-as periodicity
in the GaN electron and hole system is revealed by the quantum interference constructed with the two
transitions from the valence and conduction band states, which are probed by an extremely short isolated
attosecond pulse with a coherent broadband spectrum. The resultant dipole frequency reaches 1.16 PHz
(1015 Hz), making this the first time the petahertz frequency barrier has been exceeded with
semiconductor. This study shows the potential of future petahertz signal processing technology based on
ordinary wide-bandgap semiconductor devices.
