  Laser technology has developed and accelerated photo-induced nonequilibrium
physics from both scientific and engineering viewpoints. The Floquet
engineering, i.e., controlling material properties and functionalities by
time-periodic drives, is a forefront of quantum physics of light-matter
interaction, but limited to ideal dissipationless systems. For the Floquet
engineering extended to a variety of materials, it is vital to understand the
quantum states emerging in a balance of the periodic drive and energy
dissipation. Here we derive the general description for nonequilibrium steady
states (NESS) in periodically driven dissipative systems by focusing on the
systems under high-frequency drive and time-independent Lindblad-type
dissipation with the detailed balance condition. Our formula correctly
describes the time-average, fluctuation, and symmetry property of the NESS, and
can be computed efficiently in numerical calculations. Our approach will play
fundamental roles in Floquet engineering in a broad class of dissipative
quantum systems such as atoms and molecules, mesoscopic systems, and condensed
matter.
