  The ability to manipulate the space-time structure of light waves diversifies
light-matter interaction and light-driven applications. Conventionally,
metasurfaces are employed to locally control the amplitude and phase of light
fields by the material response and structure of small meta-atoms. However, the
fixed spatial structures of metasurfaces offer limited opportunities. Here,
using quantum control we introduce a new approach that enables the amplitude,
sign, and even configuration of the generated light fields to be manipulated in
an all-optical manner. Following this approach, we demonstrate the generation
of flying doughnut terahertz (THz) pulses. We show that the single-cycle THz
pulse radiated from the dynamic semiconductor ring current has an electric
field structure that is azimuthally polarized and that the space- and
time-resolved magnetic field has a strong, isolated longitudinal component. As
a first application, we detect absorption features from ambient water vapor on
the spatiotemporal structure of the measured electric fields and the calculated
magnetic fields. Quantum control is a powerful and flexible route to generating
any structured light pulse in the THz range, while pulse compression of
cylindrical vector beams is available for very high-power magnetic-pulse
generation from the mid-infrared to near UV spectral region. Pulses such as
these will serve as unique probes for spectroscopy, imaging,
telecommunications, and magnetic materials.
