Counterintuitive Yet Efficient Regimes for Measurement-Based Quantum Computation on Symmetry-Protected Spin Chains

Quantum states picked from nontrivial symmetry-protected topological (SPT) phases have computational power in measurement-based quantum computation. This power is uniform across SPT phases, and is unlocked by measurements that break the symmetry. Except at special points in the phase, all computational schemes known to date place these symmetry-breaking measurements far apart, to avoid the correlations introduced by spurious, nonuniversal entanglement. In this work, we investigate the opposite regime of computation where the symmetry-breaking measurements are packed densely. We show that not only does the computation still function, but in fact, under reasonable physical assumptions, this is the most resource efficient mode.