Abstract：Superconductors, spin liquids, and topological semimetals are typical quantum materials currently under intensive study. In this talk, I will present our investigation of these quantum materials in recent few years by putting them under extreme conditions, such as ultralow temperature, high magnetic field, high pressure, and ultrathin flake. By measuring the ultralow-temperature thermal conductivity and specific heat, we may judge the superconducting gap structure of a novel superconductor and whether a frustrated quantum magnet has a spin liquid ground state. By measuring the quantum oscillation of the magnetoresistance under high field, we may reveal the Fermi surfaces of a topological semimetal and judge whether it is topologically nontrivial or not. By applying high pressure, we expect to induce superconductivity in a topological semimetal and get a topological superconductor candidate. Finally, by gating the ultrathin flake of a quasi-two-dimensional material, we can finely tune its ground state over a broad carrier doping range and study the quantum phase transitions.