The Anti-Lock Collapse Law introduces a universal dynamical mechanism in which collapse is triggered not by decoherence or loss of phase coherence, but by excessive persistence of modal dominance accumulated through history-load. When the participation ratio of a system drops below a critical threshold, a deterministic collapse operator redistributes amplitude and restores multi-modal dynamics. This framework unifies gravitational collapse, quantum–to–macroscopic transitions, and radio–to–optical spectral ordering through a single algebraic law. The model yields testable predictions across astrophysical and laboratory systems, including the systematic sequence radio → optical during runaway collapse and optical → radio during stabilizing collapse. Numerical simulations and observational datasets provide independent support for a universal collapse law grounded in modal complexity.
Spectral collapse in the two-photon quantum Rabi model (tpQRM) has long been regarded as insufficient to establish quantum criticality because, under generic conditions, the lowest excitation gap remains finite. We show that, at a special qubit frequency, spectral collapse in the anisotropic tpQRM constitutes a continuous quantum phase transition governed by a single soft mode. The same-parity gap, set by the vanishing effective oscillator frequency, closes with exponent
zν=1/2, whereas the lower different-parity gap arises from symmetry-induced splitting. Parity symmetry excludes the different-parity excitation from the quantum Fisher information response and restricts Kibble-Zurek dynamics to excitations within the ground-state parity sector. Together, these results identify the same-parity excitation as the soft mode and its gap as the characteristic energy scale. The corresponding critical exponents,
ν=1/4 and
z=2, place the anisotropic tpQRM in the same universality class as the standard QRM. Our results establish spectral collapse as a potential route to experimentally accessible quantum criticality in a few-body system and show that universality is determined by the soft-mode structure rather than by the closing of the lowest excitation gap.
ABSTRACT We investigate the spectral properties and quantum criticality of the two‐photon Rabi–Stark model. Using the exact solution of this model, we rigorously derive a condition for complete spectral collapse, where all bound states vanish. In this case, the energy gap closes at a critical coupling, signaling a continuous quantum phase transition. The corresponding gap exponent differs from those in both the one‐photon Rabi–Stark model and the quantum Rabi model, suggesting a distinct universality class. While in the general case, an infinite number of discrete bound states exist when spectral collapse occurs and the energy gap remains open. By mapping to an inverse square potential well, these bound levels approach the threshold energy exponentially. Our results offer new insights into novel spectral phenomena in nonlinear quantum Rabi models, with potential implications for experimental realizations in circuit quantum electrodynamics and trapped ion systems.