Chiral Zener tunneling in non-Hermitian frequency lattices

Zheng, Lingzhi; Wang, Bing; Qin, Chengzhi; Zhao, Lange; Chen, Shuyue; Liu, Weiwei; Lu, Peixiang

doi:10.1364/ol.470880

Cited by 8 publications

(4 citation statements)

References 30 publications

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“…The result indicates the complex modulation leads to complex coupling between symmetric and anti-symmetric modes. The phase difference ϕ between real and imaginary modulation acts as an effective gauge potential [40]. Its interaction with complex coupling finally leads to anisotropic coupling.…”

Section: Theoretical Model For Anisotropic Couplingmentioning

confidence: 99%

Direction-dependent non-Hermitian skin effect in modulated photonic waveguide arrays

Zou

Jiang

et al. 2022

Front. Phys.

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Non-Hermitian skin effect (NHSE), where huge modes are accumulated at system boundaries, offers new possibility for steering the transport and localization of light by non-Hermiticity. Here, the direction-dependent NHSE is proposed in a photonic waveguide array via spatially complex modulation, where the skin modes tend to localize at different boundaries for opposite propagation directions. We utilize complex modulation to arouse anisotropic coupling between symmetric and anti-symmetric modes in multimode waveguides and further match the refractive index of adjacent waveguides. In this way, a non-Hermitian Su–Schrieffer–Heeger (SSH) lattice that supports NHSE is achieved. In particular, the anisotropic coupling is highly unidirectional. For forward direction, it allows mode conversion from antisymmetric modes to symmetric modes. However, the process is forbidden for backward direction. As a result, the skin modes tend to locate at lower boundary for forward propagation but the localization direction is reversed for backward injection. Our results provide a potential platform to investigate NHSE on photonic chips and may find applications in non-magnetic unidirectional devices.

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Section: Theoretical Model For Anisotropic Couplingmentioning

confidence: 99%

Direction-dependent non-Hermitian skin effect in modulated photonic waveguide arrays

Zou

Jiang

et al. 2022

Front. Phys.

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“…In a non-Hermitian lattice, the complex Berry phase, i.e., Zak phase, naturally arises under an external dc force or a time-varying magnetic flux [81], so that a Bloch eigenstate adiabatically evolves across the entire Brillouin zone, accumulating a complex geometric phase. While the related phenomena of Bloch oscillations and Zener tunneling have been investigated to some extent in non-Hermitian lattices [90][91][92][93][94][95][96][97][98][99][100], physical signatures of the complex Zak phase have received little attention thus far, mostly restricted to some specific lattice models [66,81].…”

Section: Introductionmentioning

confidence: 99%

Complex Berry phase and imperfect non-Hermitian phase transitions

Longhi

Feng

2023

Phys. Rev. B

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In many classical and quantum systems described by an effective non-Hermitian Hamiltonian, spectral phase transitions, from an entirely real-energy spectrum to a complex spectrum, can be observed as a non-Hermitian parameter in the system is increased above a critical value. A paradigmatic example is provided by systems possessing parity-time (PT ) symmetry, where the energy spectrum remains entirely real in the unbroken PT phase while a transition to complex energies is observed in the broken PT phase. Such spectral phase transitions are universally sharp. However, when the system is slowly and periodically cycled, the phase transition can become smooth, i.e., imperfect, owing to the complex Berry phase associated to the cyclic adiabatic evolution of the system. This remarkable phenomenon is illustrated by considering the spectral phase transition of the Wannier-Stark ladders in a PT -symmetric class of two-band non-Hermitian lattices subjected to an external dc field, revealing that a nonvanishing imaginary part of the Zak phase-the Berry phase picked up by a Bloch eigenstate evolving across the entire Brillouin zone-is responsible for imperfect spectral phase transitions.

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“…Zak phase, naturally arises under an external dc force or a time-varying magnetic flux [81], so that a Bloch eigenstate adiabatically evolves across the entire Brillouin zone accumulating a complex geometric phase. While the related phenomena of Bloch oscillations and Zener tunneling have been investigated at some extent in non-Hermitian lattices [90][91][92][93][94][95][96][97][98][99][100], physical signatures of the complex Zak phase have received so far little attention and mostly restricted to some specific lattice models [66,81].…”

Section: Introductionmentioning

confidence: 99%

Complex Berry phase and imperfect non-Hermitian phase transitions

Longhi¹,

Li²

2023

Preprint

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In many classical and quantum systems described by an effective non-Hermitian Hamiltonian, spectral phase transitions, from an entirely real energy spectrum to a complex spectrum, can be observed as a non-Hermitian parameter in the system is increased above a critical value. A paradigmatic example is provided by systems possessing parity-time (PT ) symmetry, where the energy spectrum remains entirely real in the unbroken PT phase while a transition to complex energies is observed in the unbroken PT phase. Such spectral phase transitions are universally sharp. However, when the system is slowly and periodically cycled, the phase transition can become smooth, i.e. imperfect, owing to the complex Berry phase associated to the cyclic adiabatic evolution of the system. This remarkable phenomenon is illustrated by considering the spectral phase transition of the Wannier-Stark ladders in a PT -symmetric class of two-band non-Hermitian lattices subjected to an external dc field, unraveling that a non-vanishing imaginary part of the Zak phase -the Berry phase picked up by a Bloch eigenstate evolving across the entire Brillouin zone-is responsible for imperfect spectral phase transitions.

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Chiral Zener tunneling in non-Hermitian frequency lattices

Cited by 8 publications

References 30 publications

Direction-dependent non-Hermitian skin effect in modulated photonic waveguide arrays

Direction-dependent non-Hermitian skin effect in modulated photonic waveguide arrays

Complex Berry phase and imperfect non-Hermitian phase transitions

Complex Berry phase and imperfect non-Hermitian phase transitions

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