Strong Hilbert space fragmentation via emergent quantum drums in two dimensions

We introduce a disorder-free model of $S=1/2$ spins on the square lattice in constrained Hilbert space where two up-spins are not allowed simultaneously any neighboring sites lattice. The interactions given by ring-exchange terms elementary plaquettes that conserve both total magnetization as well dipole moment. show this provides tractable example strong fragmentation dimensions with typical initial states evading thermalization respect to full space. Given product state, system can be decomposed into disjoint spatial regions made edge and/or vertex sharing we dub ``quantum drums''. These quantum drums come many shapes and sizes specifying belong drum fixes its spectrum. spectra some small is calculated analytically. study bigger quasi-one-dimensional numerically, dubbed ``wire'' ``junction wires'' respectively. find these possess chaotic spectrum but also support distinct families many-body scars cause periodic revivals from different states. wire shown equivalent one-dimensional PXP chain open boundaries, paradigmatic for scarring; while junction wires represents model.