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Register a new userOne-sided destructive quantum interference from an exceptional point-enabled metasurface
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We propose the concept of one-sided quantum interference based on non-Hermitian metasurfaces.By designing bianisotropic metasurfaces with a non-Hermitian exceptional point, we show that quantum interference can exist only on only one side but not another. This is the quantum inheritance of unidirectional zero reflection in classical optics.The one-side interference can be further manipulated with tailor-made metasurface. With two photons simultaneously entering the metasurface from different sides, the probability for only outputting one photon on the side with reflection can be modified to zero as a one-sided destructive quantum interference while the output on another side is free of interference. We design the required bianisotropic metasurface and numerically demonstrate the proposed effect. The non-Hermitian bianisotropic metasurfaces provide more degrees of freedom in tuning two-photon quantum interference, in parallel to the celebrated Hong-Ou-Mandel effect.
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Optical metasurfaces open new avenues for precise wavefront control of light for integrated quantum technology. Here, we demonstrate a hybrid integrated quantum photonic system that is capable to entangle and disentangle two-photon spin states at a dielectric metasurface. By interfering single-photon pairs at a nanostructured dielectric metasurface, a path-entangled two-photon NOON state with circular polarization is generated that exhibits a quantum HOM interference visibility of 86 $pm$ 4%. Furthermore, we demonstrate nonclassicality and phase sensitivity in a metasurface-based interferometer with a fringe visibility of 86.8 $pm$ 1.1 % in the coincidence counts. This high visibility proves the metasurface-induced path entanglement inside the interferometer. Our findings provide a promising way to hybrid-integrated quantum technology with high-dimensional functionalities in various applications like imaging, sensing, and computing.
Dynamically varying system parameters along a path enclosing an exceptional point is known to lead to chiral mode conversion. But is it necessary to include this non-Hermitian degeneracy inside the contour for this process to take place? We show that a slow enough variation of parameters, even away from the systems exceptional point, can also lead to a robust asymmetric state exchange. To study this process, we consider a prototypical two-level non-Hermitian Hamiltonian with a constant coupling between elements. Closed form solutions are obtained when the amplification/attenuation coefficients in this arrangement are varied in conjunction with the resonance detuning along a circular contour. Using asymptotic expansions, this input-independent mode conversion is theoretically proven to take place irrespective of whether the exceptional point is enclosed or not upon encirclement. Our results significantly broaden the range of parameter space required for the experimental realization of such chiral mode conversion processes.
We consider a two-dimensional nonlinear waveguide with distributed gain and losses. The optical potential describing the system consists of an unperturbed complex potential depending only on one transverse coordinate, i.e., corresponding to a planar waveguide, and a small non-separable perturbation depending on both transverse coordinates. It is assumed that the spectrum of the unperturbed planar waveguide features an exceptional point (EP), while the perturbation drives the system into the unbroken phase. Slightly below the EP, the waveguide sustains two-component envelope solitons. We derive one-dimensional equations for the slowly varying envelopes of the components and show their stable propagation. When both traverse directions are taken into account within the framework of the original model, the obtained two-component bright solitons become metastable and persist over remarkably long propagation distances.
Previous research has attempted to minimize the influence of loss in reflection- and transmission-type acoustic metasurfaces. This letter shows that, by treating the acoustic metasurface as a non-Hermitian system and by harnessing loss, unconventional wave behaviors that do not exist in lossless metasurfaces can be uncovered. Specifically, we theoretically and experimentally demonstrate a non-Hermitian acoustic metasurface mirror featuring extremely asymmetrical reflection at the exception point. As an example, the metasurface mirror is designed to have high-efficiency retro-reflection when the wave incidents from one side and complete absorption when the wave incidents from the other side. This work marries conventional gradient index metasurfaces with the exception point from non-Hermitian systems, and paves the way for identifying new mechanisms and functionalities for wave manipulation.
An experimental setup of three coupled $mathcal{PT}$-symmetric wave guides showing the characteristics of a third-order exceptional point (EP3) has been investigated in an idealized model of three delta-functions wave guides in W.~D. Heiss and G.~Wunner, J. Phys. A 49, 495303 (2016). Here we extend these investigations to realistic, extended wave guide systems. We place major focus on the strong parameter sensitivity rendering the discovery of an EP3 a challenging task. We also investigate the vicinity of the EP3 for further branch points of either cubic or square root type behavior.
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