Study On Unidirectional Reflectionlessness And Non-reciprocal Quantum Entanglement In A Non-hermitian Quantum System

Quantum mechanics is a kind of physics theory that studies microscopic matter,while observable quantities play an important indicator in describing the properties of matter.The observable physical quantity has always been expressed by Hermi-tian operator in the quantum mechanics.In 1998,Bender et al.proposed that if the non-Hermitian operators can have fully real eigenvalues under the condition of parity-time(PT)symmetry,it would be observable physical quantities.One of the most notable features of PT system is the existence of exceptional point(EP)that has been researched in a wide range of quantum systems and classical optical systems.In classical optical systems,a series of fascinating phenomena occur,such as optical isolation,non-reciprocal light propagation,coherent perfect absorption,unidirectional reflectionlessness.Recently,since surface plasmon or photon was considered as ideal carriers of quantum information,an important topic for the transport properties of single sur-face plasmon or photon in one dimensional(1D)waveguide was investigated by many researchers in Hermitian and non-Hermitian systems.Up to now,most of the pre-vious studies focus on the transport properties of single photon or surface plasmon interacting with quantum emitters in one direction.However,non-reciprocal trans-port properties of single plasmon or photon interacting with quantum dots(QDs)coupled to 1D waveguide in non-Hermitian system has rarely been considered yet.In this letter,we put forward an approach to realize the unidirectional reflectionless-ness and non-reciprocal quantum entanglement at EP in a non-Hermitian system.The main contents of this work are as follows.(1)We investigate the unidirectional reflectionless propagation of surface plasmon in non-Hermitian quantum system.The non-Hermitian quantum sys-tem consists of a surface plasmon coupling to two quantum dots(QDs)in a metal nanowire.By appropriately tuning the phase difference between two quantum dots,we demonstrate the unidirectional reflectionless propagation of surface plasmon at exceptional point.(2)Unidirectional reflectionlessness is demonstrated in a non-Hermitian quan-tum system that consists of a fibre-taper waveguide side coupled to a whispering-gallery-mode microresonator(WGMM)interacting with two separated QDs.In our scheme,the unidirectional reflectionlessness is obtained at EP by adjusting the phase shifts between two QDs.Moreover,non-reciprocal quantum entanglement between two QDs is analyzed and the concurrence at EP reaches～1.More importantly,our non-Hermitian system at EP has two same real eigenvalues of 0.