  Photon number-squeezed states are of significant value in fundamental quantum
research and have a wide range of applications in quantum metrology. Most of
their preparation mechanisms require precise control of quantum dynamics and
are less tolerant to dissipation. We propose a mechanism that is not subject to
these restraints. In contrast to common approaches, we exploit the
self-balancing between two types of dissipation induced by positive- and
negative-temperature reservoirs to generate steady states with sub-Poissonian
statistical distributions of photon numbers. We also show how to implement this
mechanism with cavity optomechanical systems. The quality of the prepared
photon number-squeezed state is estimated by our theoretical model combined
with realistic parameters for various typical optomechanical systems.
