Quantum fluids, from superconducting electrons to superfluid helium, from BEC ultracold atoms on optical lattices, to cosmological-scale superfluid core in neutron stars, embody the most profound quantum behaviors of a many-particle world. The theories which explained such incredible phenomena count among the greatest achievements in theoretical many-body physics, and have had profound implications in many other areas, such as the standard model of particle physics. Gain-dissipative exciton-polaritons systems have recently emerged as promising solid-state platforms for complex quantum many-body simulations. However, a room-temperature polariton platform remains a holy grail due to material limitations. This dissertation presents a consistent endeavor to construct a robust room-temperature exciton-polariton platform using solution-based nanoconfined synthesis and study these fascinating quantum fluid phenomena.

The first part of the dissertation developed a solution-based single crystal growth method by the combination of top-down nanofabrication and bottom-up chemical synthesis in the fabricated two-dimensional confined nanocavity. We demonstrate crystal growth under such nanometer confinement shows four major unique advantages, namely, nanometer-precise thickness control, large grain size, excellent excitonic quality, and sub-nanometer surface homogeneity, all thanks to the special nanoconfined environment. These four major advantages overcome the material limitations and enable us to explore, in the second part of the dissertation, for the first time, the landmark experiments of quantum fluid phase transitions at room temperature: from a normal fluid to both a zero-viscosity superfluid and a Čerenkov supersonic fluid, the unambiguous signatures of Landau criterion in quantum fluids. In addition, the results are in excellent quantitative agreement with our theoretical modeling using nonequilibrium Gross-Pitaevskii equations and the steady-state Bogoliubov excitation spectra analysis. In the third part of the dissertation, we demonstrate, for the first time, XY Hamiltonian graph simulator with the nanoconfined-synthesized crystals at room temperature. We show that lattice with a large number of coherently coupled condensates up to 10×10 can be achieved, which is a significant step towards the ultimate goal of realizing a room-temperature polaritonic platform. In the last chapter, we extend the two-dimensional confined synthesis to surface confinement and study its effect on crystal morphologies.