  Quantum spin liquids (QSLs) are exotic phases with intrinsic massive
entanglements. Instead of microscopic spins, fractionalized particles and gauge
fluctuations are emergent, revealing QSLs' exotic natures. Quantum spins with
strong spin-orbit coupling on a pyrchlore lattice, for example Pr2Zr2O7, are
suggested to host a U(1) QSL with emergent photons, gapless excitations without
breaking any symmetries, as well as emergent monopoles. One of the key issues
in QSLs is an interplay between emergent degrees of freedom of QSLs and
conventional degrees of freedom, and we investigate the interplay by
constructing a general theory of spin-lattice coupling in U(1) QSLs. We find
that the coupling induces characteristic interplay between phonons and photons.
For example, photons become qualitatively more stable than phonons at low
temperature. We also propose mechanisms to detect emergent photons in
experiments such as sound attenuation and thermal transport relying on
spin-lattice coupling in U(1) QSLs.
