  Superlenses made of plasmonic materials and metamaterials have been exploited
to image features of sub-diffractional scale. However, their intrinsic losses
impose a serious restriction on the imaging resolution, which is a
long-standing problem that has hindered wide-spread applications of
superlenses. Optical waves of complex frequency exhibiting a temporally
attenuating behavior have been proposed to offset the intrinsic losses in
superlenses via virtual gain, but the experimental realization has been missing
due to the challenge involved in preparing the illumination with temporal
decay. Here, by employing multi-frequency measurement, we successfully
implement a synthetic optical wave of complex frequency to experimentally
observe deep-subwavelength superimaging patterns enabled by the virtual gain.
Our work represents a practical approach to overcoming the intrinsic losses of
plasmonic systems for imaging and sensing applications.
