Topology in parity-time-symmetric quantum walks  

作　　者：XUE Peng 薛鹏(Beijing Computational Science Research Center)

机构地区：[1]Beijing Computational Science Research Center,Beijing 100084,China

出　　处：《Science Foundation in China》2019年第3期70-80,共11页中国科学基金（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.11674056 and U1930402);the Natural Science Foundation of Jiangsu Province(Grant No.BK20160024);the startup funding of Beijing Computational Science Research Center

摘　　要：The study of non-Hermitian systems with parity-time(PT)symmetry is a rapidly developing frontier in recent years?Experimentally,PT-symmetric systems have been realized in classical optics by balancing gain and loss,which holds great promise for novel optical devices and networks?Here we report experimental realization of passive PT-symmetric quantum dynamics for single photons by temporally alternating photon losses in the quantum walk(QW)interferometers.The ability to impose PT symmetry allows us to realize and investigate Floquet topological phases driven by PT-symmetric QWs.We observe topological edge states between regions with different topological invariants?Topological invariants can be defined by winding numbers,Zak phases,general geometry phases and can be calculated?Can they be detected directly?We give an answer by reporting the experimental detection of bulk topological invariants in non-unitary QWs?The topological invariant of the non-unitary quantum walk is manifested in the quantized average displacement of the walker,which is probed by monitoring the photon loss.Furthermore,we report the experimental study of dynamic quantum phase transitions(DQPTs)and photonic skyrmions using discrete-time QWs?We simulate quench dynamics between distinct Floquet topological phases using quantum-walk dynamics,and experimentally characterize DQPTs and emergent skyrmion structures.Our results pave the way for realizing quantum mechanical PT-synthetic devices and augurs exciting possibilities for exploring topological properties of non-Hermitian systems using discretetime QWs.The study of non-Hermitian systems with parity-time(PT) symmetry is a rapidly developing frontier in recent years. Experimentally, PT-symmetric systems have been realized in classical optics by balancing gain and loss, which holds great promise for novel optical devices and networks. Here we report experimental realization of passive PT-symmetric quantum dynamics for single photons by temporally alternating photon losses in the quantum walk(QW) interferometers. The ability to impose PT symmetry allows us to realize and investigate Floquet topological phases driven by PT-symmetric QWs. We observe topological edge states between regions with different topological invariants. Topological invariants can be defined by winding numbers, Zak phases, general geometry phases and can be calculated. Can they be detected directly? We give an answer by reporting the experimental detection of bulk topological invariants in non-unitary QWs. The topological invariant of the non-unitary quantum walk is manifested in the quantized average displacement of the walker, which is probed by monitoring the photon loss. Furthermore, we report the experimental study of dynamic quantum phase transitions(DQPTs) and photonic skyrmions using discrete-time QWs. We simulate quench dynamics between distinct Floquet topological phases using quantum-walk dynamics, and experimentally characterize DQPTs and emergent skyrmion structures. Our results pave the way for realizing quantum mechanical PT-synthetic devices and augurs exciting possibilities for exploring topological properties of non-Hermitian systems using discrete-time QWs.

关 键 词：QUANTUM WALKS Parity-time symmetry Dynamic QUANTUM phase TRANSITIONS Photonic SKYRMIONS 

分 类 号：O41[理学—理论物理]