Researchers have discovered a new type of quantum spin liquid, dubbed a gapless fracton quantum spin liquid, in a theoretical two-dimensional spin-1 model. This finding is significant because quantum spin liquids are exotic states of matter that do not order their spins in a conventional way, but instead exhibit long-range quantum entanglement. The particularity of this new state is its "gapless" nature, meaning there is no minimum energy to excite the system, and the emergence of "photons" as low-energy excitations, which distinguishes it from other known spin liquids.

The concept of fractons, which are excitations with restricted mobility, has been an area of intense research in condensed matter physics. Until now, studied fracton spin liquids typically had an energy gap (gapped), meaning they required a minimum energy to generate excitations. The identification of a gapless fracton state in two dimensions, and the association of its excitations with particles that behave like photons, opens new avenues for understanding the interplay between topology and quantum dynamics in many-body systems. This theoretical model could serve as a basis for the design of new quantum materials with exotic properties.

This advance is based on a spin-1 model, more complex than the commonly studied spin-1/2 models, allowing for a greater richness of quantum phenomena. The emergence of photons in this context does not refer to actual light particles, but to collective excitations of the system that exhibit photon-like properties, such as being massless and propagating at a constant speed. Understanding these exotic states is crucial for the development of future quantum technologies, including fault-tolerant quantum computing and high-precision quantum sensing, as the stability of quantum information often depends on the topological nature of the ground state.