| Summary: | Since the quantum concept of parity-time (PT) symmetry has been introduced into the conventional inductor–capacitor resonance, strategies based on exceptional points (EP) based strategies redefine our understanding of sensitivity limitation. This considerable enhancement of sensitivity originated in exploration of the non-Hermitian physics in photonics, acoustics and electronics, which exhibits a substantial application to the miniaturization of implanted electronic sensors in medicine field. By continuously accessing the EP, the spectral response of reader ∆ ω follows a dependency of Δ ω ∼ κ ^2/3 to a weakly coupling rate (| κ | ≈ 0), which may approach the theoretical limit of sensitivity in a second-order EP system. In this paper, we experimentally demonstrate a high-order (higher than second-order) PT symmetric system for weak coupling detection, in which a third-order EP can be employed to fulfill the sensitivity of Δ ω ∼ κ ^1/2 . Particularly, we introduce the incoming wave as an effective gain to balance the loss and obtain a pair of purely real eigenfrequencies. There are absence of imaginary parts despite corresponding real parts shifts dramatically by using a neutral resonator, without a broadening of the reflection spectrum so that maintaining a high resolution on the sensitivity. This work may reveal the physical mechanics of a small perturbation at a high-order EP and promote applications in implanted medicine devices.
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