Parity-time-symmetric quantum critical phenomena

TLDR

PT‑symmetric nonconservative systems can undergo spontaneous symmetry breaking accompanied by spectral singularity, yet prior work in optics and weakly interacting open quantum systems has not incorporated many‑body correlations. The authors extend PT symmetry to strongly correlated many‑body systems to uncover a new universality class that combines spectral singularity with quantum criticality, a phenomenon absent in known critical behaviors. The study reveals a novel universality class arising from the interplay of spectral singularity and quantum criticality in PT‑symmetric many‑body systems, exhibiting unconventional low‑dimensional quantum criticality with anomalously enhanced superfluid correlations driven by non‑monotonic RG flows, contrasting the BKT paradigm and offering experimentally testable predictions in ultracold atoms beyond the Hermitian framework.

Abstract

Synthetic nonconservative systems with parity-time (PT) symmetric gain-loss structures can exhibit unusual spontaneous symmetry breaking that accompanies spectral singularity. Recent studies on PT symmetry in optics and weakly interacting open quantum systems have revealed intriguing physical properties, yet many-body correlations still play no role. Here by extending the idea of PT symmetry to strongly correlated many-body systems, we report that a combination of spectral singularity and quantum criticality yields an exotic universality class which has no counterpart in known critical phenomena. Moreover, we find unconventional low-dimensional quantum criticality, where superfluid correlation is anomalously enhanced owing to non-monotonic renormalization group flows in a PT-symmetry-broken quantum critical phase, in stark contrast to the Berezinskii-Kosterlitz-Thouless paradigm. Our findings can be experimentally tested in ultracold atoms and predict critical phenomena beyond the Hermitian paradigm of quantum many-body physics.