The study reframes loss in open photonic systems as an intrinsic, controllable property, showing loss can be engineered to enable directional light transport through nonreciprocal dynamic degeneracy splitting in gyromagnetic photonic crystals.

Experiments with phased dipole source arrays reveal long-lived bulk modes propagate in one direction while counter-propagating modes decay rapidly, as confirmed by Fourier-space analysis and near-field measurements.

The authors outline a broader framework called complex-band dynamical engineering, where both the real and imaginary parts of the band structure are designed together to select propagation channels by lifetime.

This bulk-based approach contrasts with prior surface- or Weyl-state methods, offering a potentially simpler route to nonreciprocal transport and imaging via dissipation engineering.

Directional imaging at 7.8 GHz achieved a focal spot of about 0.81 wavelengths, forward imaging efficiency of 0.495, backward efficiency of 0.026, and isolation up to 4.8 dB, using bulk states rather than surface states.

The experimental platform is a microwave-range gyromagnetic photonic crystal with sequential symmetry breaking: static magnetic field to break time-reversal symmetry, displacement of a ceramic pillar to induce anisotropic, hyperbolic-like dispersion, and intentional absorbers to tailor loss distribution.

Potential extensions include other lattice geometries, multiband systems, and synthetic dimensions, with applications in mode-selective transport, nonreciprocal frequency conversion, and frequency-domain routing.

Two waves sharing the same real frequency can have different lifetimes due to momentum-dependent overlap with lossy regions, enabling propagation in one direction while suppressing the opposite.

Loss is transformed from a scalar nuisance into a structured, direction-sensitive filter, enabling directional transport and imaging without altering the real-frequency band structure.