Has emergent quantum electrodynamics been observed in a quantum spin ice?
In plain words
Quantum spin ice should host three kinds of emergent particles: photons, electric-like spinons and magnetic monopoles. Cerium pyrochlores such as Ce2Zr2O7 show signs of these, but alternative explanations are not fully excluded.
Precise statement
In Ce2Zr2O7, Ce2Sn2O7 and Ce2Hf2O7 (dipolar-octupolar doublets), establish the $\mathrm{U}(1)$ quantum spin liquid through its distinct signatures: a gapless linearly dispersing transverse photon ($C \sim T^{3}$ well below the photon bandwidth), a spinon continuum, and their predicted spectral weights. An answer is a fit of thermodynamic and neutron data by quantum spin ice theory with independently fixed exchange parameters that excludes classical or disorder-driven alternatives.
What would settle it
Polarized neutron scattering below $0.05\,\mathrm{K}$ resolving the low-energy photon mode and heat capacity showing the $T^3$ term, both matched to quantum Monte Carlo of the fitted XYZ model.
Status in the literature
Unverified note
Gao et al. (Nature Physics 2025) reported neutron and thermodynamic evidence for emergent photons and spinons in Ce2Zr2O7, interpreted as a pi-flux quantum spin ice.