Interacting artificial many-body systems play a fundamental role in the development of quantum simulators. Using engineered photonic systems, it has recently become possible to realize strongly interacting photon gases, which are particularly well suited for probing non-equilibrium many-body physics. The driven-dissipative nature of these systems is a major reason for the interest in them. Radiative losses are crucial to obtain real-time experimental access to the dynamical evolution of the quantum fluid, while new quantum phases of matter are expected to appear in such non-equilibrium many-body scenarios. These developments require novel theoretical tools to describe and understand them.

The research field of photonic quantum simulators is highly interdisciplinary in nature, attracting researchers from diverse fields such as quantum optics, condensed matter physics, statistical mechanics and quantum information science. Experiments cover a wide range of systems, ranging from circuit-QED systems in the microwave domain to optical and exciton-polariton systems. The goal of this program is to help in shaping this community and setting the agenda for future research. 

Key questions to be addressed include: 

• What are the scalable approaches for mediating strong photon-photon interactions?
  
• What are the promising methods to prepare driven-dissipative many-body state?
  
• What are the relevant observables in such systems?
  
• What are the collective properties of such driven-dissipative systems and how can exotic states of matters be created?
  
• How can one identify many-body features that are unique to driven-dissipative systems?