Physicalism is the view that no “element of reality” (Einstein) is missing from the mathematical equations of physics – more strictly, tomorrow’s physics beyond the Standard Model plus GR.
Idealism is the view that reality is experiential.
Most physicalists aren’t idealists, and most idealists aren’t physicalists, but a small minority of researchers are both idealists and physicalists.
The intrinsic nature of quantum states is disputed. But if quantum mechanics is complete, and if the equations of physics describe fields of sentience rather than insentience, then physicalistic idealism is true. If so, there is no Hard Problem of consciousness as normally framed. Fields of insentience are destined to go the way of luminiferous aether. Formally, physical reality is described by the universal wavefunction. By contrast, consciousness is often said to be ill-defined. Yet if physicalistic idealism is true, then we already possess the mathematical apparatus of a theory of consciousness. All that’s hard is to “read off” the textures of experience from the solutions to the equations. The conjecture that relativistic QFT describes fields of sentience rather than insentience still leaves the mystery of why anything exists for the equations to describe: one big mystery rather than two. Yet even here, the superposition principle of QM hints at an answer.