  Active nematics are materials composed of mobile, elongated particles that
can transform energy from the environment into a mechanical motion. Current
experimental realizations of the active nematics are of biological origin and
include cell layers, suspensions of elongated bacteria in liquid crystal, and
combinations of bio-filaments with molecular motors. Here, we report the
realization of a fully synthetic active nematic system comprised of a lyotropic
chromonic liquid crystal energized by ultrasonic waves. This artificial active
liquid crystal is free from biological degradation and variability, exhibits
stable material properties, and enables precise and rapid activity control over
a significantly extended range. We demonstrate that the energy of the acoustic
field is converted into microscopic extensile stresses disrupting long-range
nematic order and giving rise to an undulation instability, development of
active turbulence, and proliferation of topological defects. We reveal the
emergence of unconventional free-standing persistent vortices in the nematic
director field at high activity levels. The results provide a foundation for
the design of externally energized active nematic fluids with stable material
properties and tunable topological defects dynamics crucial for the realization
of reconfigurable microfluidic systems.
