Parity-time symmetric coupled asymmetric dimers

TL;DR

This paper explores a PT-symmetric coupled asymmetric dimer system where magnetic flux influences phase transitions, exceptional points, and enhances sensing capabilities through high-order degeneracies.

Contribution

It introduces a novel PT-symmetric system with magnetic flux control, revealing reentrant phase transitions, exceptional point topology, and enhanced sensing near four-state coalescence.

Findings

Magnetic flux controls PT phase transition.

High-order exceptional points are realizable.

Enhanced sensing sensitivity at four-state coalescence.

Abstract

We investigate a parity-time (PT) symmetric system that consists of two symmetrically coupled asymmetric dimers. The enclosed magnetic flux controls the PT phase transition. The system can reenter the exact PT-symmetric phase from a broken PT-symmetric phase with large non-Hermiticity. Two-state coalescence may have one or two defective eigenstates. The topology of exceptional points is reflected by the magnetic flux independent phase rigidity scaling exponents. The topology changes when exceptional points coincide. The geometric phases accumulate when encircling the exceptional points and vary as the magnetic flux. The magnetic flux is favorable for the realization of high-order exceptional points. A triple point of different quantum phases has an order of four. The perturbation around the four-state coalescence leads to a fourth-root mode frequency splitting; the sensing sensitivity is significantly enhanced.