The (very late) advent of Quantum Acoustics with application to strange metals*

Quantum optics spans the gamut from photons to coherent states, including their classical limit, the electromagnetic field. Quantum acoustics should be parallel to quantum optics, with the phonon playing to role of photon (particles that can be counted), and the coherent states leading to classical fields (electromagnetic or sound waves) in both cases. However, it has not developed that way until recently (D. Kim et. al., references). This could have happened right after Hanbury-Brown Twiss in the late 1960's, when quantum optics was born, but did not. The coherent state limit demands a (perhaps unpopular) time dependent formulation, and has been disparaged as a kind of curiosity, with Ashcroft and Mermin warning in a short note that there is "no new physics" in the wave picture of lattice vibrations (chpt. 24). This statement is almost equivalent to saying that there is no new physics in the time dependent Schroedinger equation since we already have to the time independent Schroedinger equation. The point is that the approximations spun off the two pictures are very different and have completely different powers of computation and insight. That leads to new physics. Many of the strange metal mysteries, including Planckian resistivity, the Mott-Ioffe Regel bypass, and displaced Drude peaks, emerge from the quantum acoustics formulation. We now have a nonperturbative, coherent electron-phonon tool, including an interacting "electron wave-on-lattice wave" code, which is yielding a treasure trove of insight.