Anti-PT Symmetry Induced Real axis Bifurcation and Petermann Limited Emission Control

We theoretically analyze emission dynamics in systems exhibiting anti-parity time (anti-PT) symmetry, revealing a distinct mechanism of radiation enhancement driven by real axis mode bifurcation in the broken phase. Unlike conventional PT-symmetric systems, where eigenmodes split along the imaginary axis and emission enhancement occurs at the exceptional point (EP), anti-PT symmetry induces real frequency splitting that enhances emission away from the EP. This difference fundamentally alters the role of non-Hermitian coupling in light–matter interaction. Although both PT and anti-PT systems exhibit divergence of the Petermann factor at the EP, our analysis shows that in anti-PT systems, the local density of states (LDOS) peaks in the real frequency shifting region, enabling strong emission with reduced noise amplification. To illustrate this concept, we implement a coupled split-ring resonator (SRR) system where the coupling strength controls the real axis resonance shift, resulting in observable enhancement of radiation. These results highlight that anti-PT symmetry enables tunable, low-noise coherent emission beyond the limits imposed by conventional PT symmetric and Hermitian systems.