Quantum state texture of dynamical criticality

Abstract: We investigate the role of quantum state texture in dynamical quantum phase transitions by establishing a direct connection between critical nonequilibrium dynamics and the recently introduced notion of rugosity, a measure of the quantum state texture. Considering a generic quench protocol, we analyze both standard formulations of the dynamical quantum phase transition. For type-I transitions, defined through the long-time behavior of an order parameter, we show that the time averaged rugosity, evaluated in the eigenbasis of the pre-quench Hamiltonian, acts itself as an order parameter, sharply distinguishing the dynamical phases. In the Lipkin-Meshkov-Glick model, this behavior is traced back to the underlying semiclassical structure, where the crossing of the excited-state quantum phase transition separatrix controls the redistribution of the state over the pre-quench energy basis. For type-II transitions, characterized by nonanalyticities in the Loschmidt rate function, we demonstrate that rugosity acquires a universal interpretation. For a suitable choice of basis, the rate function is exactly given by the density of rugosity, establishing a model-independent equivalence. Moreover, we show that even in physically motivated bases, such as the pre-quench energy eigenbasis, rugosity provides clear signatures of dynamical criticality. Our results place rugosity within a broader class of quantities diagnosing dynamical quantum phase transitions, including complexity and entropy production, while highlighting its distinct role as a measure of a basis-dependent quantum resource. This work provides an information-theoretic perspective on dynamical critical phenomena and opens new directions for exploring quantum texture in nonequilibrium many-body systems.