Beyond Calabrese-Cardy Scaling: Exceptional-Point Sensitivity from the de Sitter RT Surface

Researchers have discovered a deviation from the typical Calabrese-Cardy scaling in one-dimensional critical systems, specifically in non-Hermitian critical chains near exceptional points. The biorthogonal entropy of a finite system exhibits an additional sensitivity to a small energy gap, even when this gap is smaller than the inverse system size. This newfound sensitivity introduces an interval-independent contribution to the entropy, beyond the usual Calabrese-Cardy term. The discovery sheds light on the behavior of entanglement entropy in non-Hermitian systems, which is crucial for understanding quantum phenomena in such environments. The findings indicate that the biorthogonal entropy can retain information about the energy gap, even when it is relatively small¹. This matters to practitioners because it highlights the need to reconsider the role of exceptional points in quantum systems, particularly when designing and analyzing quantum devices and simulations.