Dynamical quantum phase transitions (DQPTs) occur when a quantum system is quenched — suddenly changed — and the subsequent time evolution passes through a critical point. The standard markers are a divergence in the rate function and a jump in the dynamical topological order parameter. Mitra and Srivastava show that neither marker captures the underlying cause.
What actually drives a DQPT is symmetry restoration. After a quench, certain modes evolve to zero energy — dynamical critical modes. But not all zero-energy modes produce a DQPT. Only those whose eigenvectors restore the broken spin-flip symmetry qualify. The zero-energy condition is necessary but not sufficient. The symmetry is what matters.
This is a conceptual demotion of the traditional markers. The rate function divergence and topological jumps are downstream consequences of symmetry restoration, not independent phenomena. They co-occur because they share a cause, not because one causes the other.
The shift matters for prediction. If you track only the rate function, you see the DQPT but can't predict it — the divergence is the transition, not a precursor. If you track mode dynamics, you can see symmetry restoration approaching before the divergence occurs. The cause is visible earlier than the effect.
The structural point: in equilibrium physics, the separation between “what causes the transition” and “what marks the transition” was resolved decades ago (order parameters, symmetry breaking). In dynamical transitions, that separation was still conflated. Zero-energy modes are what mark the transition. Symmetry restoration is what causes it.