アイテム詳細

要旨

The time it takes to switch on and off electric current determines the rate at which signals can be processed and sampled in modern information technology ^{1, 2, 3, 4}. Field-effect transistors ^{1, 2, 3, 5, 6} are able to control currents at frequencies of the order of or higher than 100 gigahertz, but electric interconnects may hamper progress towards reaching the terahertz (10¹² hertz) range. All-optical injection of currents through interfering photoexcitation pathways ^{7, 8, 9, 10} or photoconductive switching of terahertz transients ^{11, 12, 13, 14, 15, 16} has made it possible to control electric current on a subpicosecond timescale in semiconductors. Insulators have been deemed unsuitable for both methods, because of the need for either ultraviolet light or strong fields, which induce slow damage or ultrafast breakdown ^{17, 18, 19, 20}, respectively. Here we report the feasibility of electric signal manipulation in a dielectric. A few-cycle optical waveform reversibly increases—free from breakdown—the a.c. conductivity of amorphous silicon dioxide (fused silica) by more than 18 orders of magnitude within 1 femtosecond, allowing electric currents to be driven, directed and switched by the instantaneous light field. Our work opens the way to extending electronic signal processing and high-speed metrology into the petahertz (10¹⁵ hertz) domain.