Achieving strong light-matter interaction at the quantum level has always been a central task in quantum physics since the emergence of quantum information and quantum control. However, the scale mismatch between the quantum emitters (nanometers) and photons (micrometers) makes the task challenging. Metallic nanostructures resolve the mismatch by squeezing the light into nanoscale volume, but their severe dissipations make quantum controls unlikely. Now, a group led by Xiao Yun-Feng at Peking University (China) has theoretically demonstrated that the strong light-matter interaction at quantum level can be achieved using microcavity-engineered metallic nanostructures. This result has been published in a recent issue of Physical Review Letters.