Scattering properties of anti-parity-time symmetric non-Hermitian system

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Abstract

We investigate the scattering properties of an anti-parity-symmetric non-Hermitian system. The anti-parity-symmetric scattering center possesses imaginary nearest-neighbor hoppings and real onsite potentials, it has been experimentally realized through dissipative coupling and frequency detuning between atomic spin waves. We find that such anti-parity-symmetric system displays three salient features: Firstly, the reflection and transmission are both reciprocal. Secondly, the reflection and transmission probabilities satisfy R+T=1 or R-T=1, which depends on the parity of the scattering center size. Thirdly, the scattering matrix satisfies (S_z)(S_z)*=I for scattering center with even-site; for scattering center with odd-site, the dynamics exhibits Hermitian scattering behavior, possessing unitary scattering matrix SS{\dag}=I.

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Exceptional points enhance sensing in an optical microcavity

Lan Yang, Guangming Zhao, Şahin Kaya Özdemir … (2017)

Sensors play an important part in many aspects of daily life such as infrared sensors in home security systems, particle sensors for environmental monitoring and motion sensors in mobile phones. High-quality optical microcavities are prime candidates for sensing applications because of their ability to enhance light–matter interactions in a very confined volume. Examples of such devices include mechanical transducers, magnetometers, single-particle absorption spectrometers, and microcavity sensors for sizing single particles and detecting nanometre-scale objects such as single nanoparticles and atomic ions. Traditionally, a very small perturbation near an optical microcavity introduces either a change in the linewidth or a frequency shift or splitting of a resonance that is proportional to the strength of the perturbation. Here we demonstrate an alternative sensing scheme, by which the sensitivity of microcavities can be enhanced when operated at non-Hermitian spectral degeneracies known as exceptional points. In our experiments, we use two nanoscale scatterers to tune a whispering-gallery-mode micro-toroid cavity, in which light propagates along a concave surface by continuous total internal reflection, in a precise and controlled manner to exceptional points. A target nanoscale object that subsequently enters the evanescent field of the cavity perturbs the system from its exceptional point, leading to frequency splitting. Owing to the complex-square-root topology near an exceptional point, this frequency splitting scales as the square root of the perturbation strength and is therefore larger (for sufficiently small perturbations) than the splitting observed in traditional non-exceptional-point sensing schemes. Our demonstration of exceptional-point-enhanced sensitivity paves the way for sensors with unprecedented sensitivity.

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An invisible acoustic sensor based on parity-time symmetry.

Romain Fleury, Dimitrios L Sounas, Andrea Alù (2015)

Sensing an incoming signal is typically associated with absorbing a portion of its energy, inherently perturbing the measurement and creating reflections and shadows. Here, in contrast, we demonstrate a non-invasive, shadow-free, invisible sensor for airborne sound waves at audible frequencies, which fully absorbs the impinging signal, without at the same time perturbing its own measurement or creating a shadow. This unique sensing device is based on the unusual scattering properties of a parity-time (PT) symmetric metamaterial device formed by a pair of electro-acoustic resonators loaded with suitably tailored non-Foster electrical circuits, constituting the acoustic equivalent of a coherent perfect absorber coupled to a coherent laser. Beyond the specific application to non-invasive sensing, our work broadly demonstrates the unique relevance of PT-symmetric metamaterials for acoustics, loss compensation and extraordinary wave manipulation.

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Erratum: Enhanced sensitivity at higher-order exceptional points

Hossein Hodaei, Absar U. Hassan, Steffen Wittek … (2017)

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Publication date Created: 27 September 2018

Article

DOI: 10.1103/PhysRevA.98.022117

ArXiV ID: 1809.10366

SO-VID: 21083e30-72f4-4143-89db-4f793b7b46a7

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http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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Journal reference Phys. Rev. A 98, 022117 (2018)

Comments 6 pages, 3 figures

Categories physics.optics

ScienceOpen disciplines: Optical materials & Optics

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ScienceOpen disciplines: Optical materials & Optics

Scattering properties of anti-parity-time symmetric non-Hermitian system

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Abstract

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Most cited references 4

Exceptional points enhance sensing in an optical microcavity

An invisible acoustic sensor based on parity-time symmetry.

Erratum: Enhanced sensitivity at higher-order exceptional points

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