Observation of exceptional points in magnonic parity-time symmetry devices

Non-Hermitian Hamiltonians may still have real eigenvalues, provided that a combined parity-time (ƤƮ) symmetry exists. The prospect of ƤƮ symmetry has been explored in several physical systems such as photonics, acoustics, and electronics. The eigenvalues in these systems undergo a transition from real to complex at exceptional points (EPs), where the ƤƮ symmetry is broken. Here, we demonstrate the existence of EP in magnonic devices composed of two coupled magnets with different magnon losses. The eigenfrequencies and damping rates change from crossing to anti-crossing at the EP when the coupling strength increases. The magnonic dispersion includes a strong “acoustic-like” mode and a weak “optic-like” mode. Moreover, upon microwave radiation, the ƤƮ magnonic devices act as magnon resonant cavity with unique response compared to conventional magnonic systems.

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Swanson hamiltonian: non-PT-symmetry phase

Journal of Physics A Mathematical and Theoretical ◽

10.1088/1751-8121/ac3a35 ◽

2021 ◽

Author(s):

Viviano Fernández ◽

Romina Ramirez ◽

Marta Reboiro

Keyword(s):

Infinite Order ◽

Model Space ◽

Pt Symmetry ◽

Negative Mass ◽

Physical Systems ◽

Exceptional Points ◽

Symmetry Phase ◽

Generalized Eigenfunctions

Abstract In this work, we study the non-hermitian Swanson hamiltonian, particularly the non-PT symmetry phase. We use the formalism of Gel’fand triplet to construct the generalized eigenfunctions and the corresponding spectrum. Depending on the region of the parameter model space, we show that the Swanson hamiltonian represents diﬀerent physical systems, i.e. parabolic barrier, negative mass oscillators. We also discussed the presence of Exceptional Points of inﬁnite order.

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Observation of non-Bloch parity-time symmetry and exceptional points

10.21203/rs.3.rs-75378/v1 ◽

2020 ◽

Author(s):

Peng Xue ◽

Lei Xiao ◽

Tianshu Deng ◽

Kunkun Wang ◽

Zhong Wang ◽

...

Keyword(s):

Brillouin Zone ◽

Skin Effect ◽

Quantum Walks ◽

Pt Symmetry ◽

Great Promise ◽

Single Photons ◽

Band Theory ◽

Exceptional Points ◽

Time Symmetry ◽

Transition Points

Abstract Parity-time (PT)-symmetric Hamiltonians have widespread significance in non-Hermitian physics. A PT-symmetric Hamiltonian can exhibit distinct phases with either real or complex eigen spectrum, while the transition points in between, the so-called exceptional points, give rise to a host of critical behaviors that holds great promise for applications. For spatially periodic non-Hermitian systems, PT symmetries are commonly characterized and observed in line with the Bloch band theory, with exceptional points dwelling in the Brillouin zone. Here, in non-unitary quantum walks of single photons, we uncover a novel family of exceptional points beyond this common wisdom. These "non-Bloch exceptional points" originate from the accumulation of bulk eigenstates near boundaries, known as the non-Hermitian skin effect, and inhabit a generalized Brillouin zone. Our finding opens the avenue toward a generalized PT-symmetry framework, and reveals the intriguing interplay among PT symmetry, non-Hermitian skin effect, and non-Hermitian topology.

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Quantum Zeno effects across a parity-time symmetry breaking transition in atomic momentum space

npj Quantum Information ◽

10.1038/s41534-021-00417-y ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Tao Chen ◽

Wei Gou ◽

Dizhou Xie ◽

Teng Xiao ◽

Wei Yi ◽

...

Keyword(s):

Symmetry Breaking ◽

State Of The Art ◽

Cold Atom ◽

Pt Symmetry ◽

Level System ◽

Flexible Control ◽

Time Symmetry ◽

Symmetry Phase ◽

Lattice Quantum ◽

Atomic Momentum

AbstractWe experimentally study quantum Zeno effects in a parity-time (PT) symmetric cold atom gas periodically coupled to a reservoir. Based on the state-of-the-art control of inter-site couplings of atoms in a momentum lattice, we implement a synthetic two-level system with passive PT symmetry over two lattice sites, where an effective dissipation is introduced through repeated couplings to the rest of the lattice. Quantum Zeno (anti-Zeno) effects manifest in our experiment as the overall dissipation of the two-level system becoming suppressed (enhanced) with increasing coupling intensity or frequency. We demonstrate that quantum Zeno regimes exist in the broken PT symmetry phase, and are bounded by exceptional points separating the PT symmetric and PT broken phases, as well as by a discrete set of critical coupling frequencies. Our experiment establishes the connection between PT-symmetry-breaking transitions and quantum Zeno effects, and is extendable to higher dimensions or to interacting regimes, thanks to the flexible control with atoms in a momentum lattice.

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Manifestation of the spontaneous parity-time symmetry breaking phase transition in hot-electron photodetection based on a tri-layered metamaterial

Nanophotonics ◽

10.1515/nanoph-2018-0207 ◽

2019 ◽

Vol 8 (3) ◽

pp. 495-504 ◽

Cited By ~ 1

Author(s):

Qiang Bai

Keyword(s):

Phase Transition ◽

Theoretical Model ◽

Symmetry Breaking ◽

Pt Symmetry ◽

Coupled Mode Theory ◽

Hot Electron ◽

Electron Device ◽

Coupled Mode ◽

Time Symmetry ◽

Existence Conditions

AbstractWe theoretically and numerically demonstrate that the spontaneous parity-time (PT) symmetry breaking phase transition can be realized respectively by using two independent tuning ways in a tri-layered metamaterial that consists of periodic array of metal-semiconductor Schottky junctions. The existence conditions of PT symmetry and its phase transition are obtained by using a theoretical model based on the coupled mode theory. A hot-electron photodetection based on the same tri-layered metamaterial is proposed, which can directly show the spontaneous PT symmetry breaking phase transition in photocurrent and possesses dynamical tunability and switchability. This work extends the concept of PT symmetry into the hot-electron photodetection, enriches the functionality of the metamaterial and the hot-electron device, and has varieties of potential and important applications in optoelectronics, photodetection, photovoltaics, and photocatalytics.

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