Background: One of the most important complications of diabetes mellitus (DM) is vision loss due to diabetic retinopathy (DR). Optical coherence tomography (OCT) provides visualization of early ...structural abnormalities of the retina and choroid. Aim: To compare retinal thickness (RT) and choroidal thickness (CT) between patients with DM without DR and healthy controls. Patients and Methods: Diabetic patients without DR were divided into two groups according to serum glycosylated hemoglobin (HbA1c) levels. Group 1: HbA1c ≤7.5 (n = 25) and group 2: HbA1c >7.5 (n = 23). The 3rd group was the healthy control group (n = 25). CT and RT measured by OCT were compared between the three groups. Results: CT in the subfoveal, temporal, and nasal quadrants was significantly higher in the healthy control group than in groups 1 and 2. Subfoveal and temporal quadrant CT in group 2 were significantly thinner than those in group 1. The average RT (ART) was thinner in group 1 than in the other groups, but there was no difference between the control group and group 2. Conclusions: This study showed that CT and ART decreased in diabetic patients without DR.
A fiber taper-based method for label-free Raman sensing is presented, which exploits the interaction between adsorbed specimen and the exposed evanescence tail of guided pump light. Chemical ...specificity and detection of microsphere specimens with diameters as small as 1 μm m are shown. To improve the sensitivity, we further propose resonator-enhanced Raman spectroscopy by taking advantage of the power build-up of a resonant mode in a cavity. Proof of concept is demonstrated by incorporating a fiber taper within a fiber ring resonator and locking a tunable laser to a circulating resonant mode. This demonstration shows a modest 40% enhancement of the Raman signal.
With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material ...limitations of silica (e.g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10(7). We compare experimentally measured Q factors with theoretical estimates, and find good agreement.
I will introduce the concepts of parity-time (PT) symmetry and exceptional points (EPs) and discuss how they can be used as a resource for sensing. I will review some of the theoretical and ...experimental breakthroughs in this direction.
Hamiltonian exceptional points (HEPs) are spectral degeneracies of non-Hermitian Hamiltonians describing classical and semiclassical open systems with gain and/or loss. However, this definition ...overlooks the occurrence of quantum jumps in the evolution of open quantum systems. These quantum effects are properly accounted for by considering Liouvillians and their exceptional points (LEPs) Minganti et al., Phys. Rev. A {\bf 100}, 062131 (2019). Here, we explicitly describe how standard quantum process tomography, which reveals the dynamics of a quantum system, can be readily applied to reveal and characterize LEPs of non-Hermitian systems. We conducted experiments on an IBM quantum processor to implement a prototype model simulating the decay of a single qubit through three competing channels. Subsequently, we performed tomographic reconstruction of the corresponding experimental Liouvillians and their LEPs using both single- and two-qubit operations. This example underscores the efficacy of process tomography in tuning and observing LEPs, despite the absence of HEPs in the model.
Non-Hermitian systems have attracted much interest in recent decades, driven partly by the existence of exotic spectral singularities, known as exceptional points (EPs), where the dimensionality of ...the system evolution operator is reduced. Among various intriguing applications, the discovery of EPs has suggested the potential for implementing a symmetric mode switch, when encircling them in a system parameter space. However, subsequent theoretical and experimental works have revealed that {\it dynamical} encirclement of EPs invariably results in asymmetric mode conversion; namely, the mode switching depends only on the winding direction but not on the initial state. This chirality arises from the failure of adiabaticity due to the complex spectrum of non-Hermitian systems. Although the chirality revealed has undoubtedly made a significant impact in the field, a realization of the originally sought symmetric adiabatic passage in non-Hermitian systems with EPs has since been elusive. In this work, we bridge this gap and theoretically demonstrate that adiabaticity, and therefore a symmetric state transfer, is achievable when dynamically winding around an EP. This becomes feasible by specifically choosing a trajectory in the system parameter space along which the corresponding evolution operator attains a real spectrum. Our findings, thus, offer a promise for advancing various wave manipulation protocols in both quantum and classical domains.
Finite simplex lattice models are used in different branches of science, e.g., in condensed matter physics, when studying frustrated magnetic systems and non-Hermitian localization phenomena; or in ...chemistry, when describing experiments with mixtures. An \(n\)-simplex represents the simplest possible polytope in \(n\) dimensions, e.g., a line segment, a triangle, and a tetrahedron in one, two, and three dimensions, respectively. In this work, we show that various fully solvable, in general non-Hermitian, \(n\)-simplex lattice models {with open boundaries} can be constructed from the high-order field-moments space of quadratic bosonic systems. Namely, we demonstrate that such \(n\)-simplex lattices can be formed by a dimensional reduction of highly-degenerate iterated polytope chains in \((k>n)\)-dimensions, which naturally emerge in the field-moments space. Our findings indicate that the field-moments space of bosonic systems provides a versatile platform for simulating real-space \(n\)-simplex lattices exhibiting non-Hermitian phenomena, and yield valuable insights into the structure of many-body systems exhibiting similar complexity. Amongst a variety of practical applications, these simplex structures can offer a physical setting for implementing the discrete fractional Fourier transform, an indispensable tool for both quantum and classical signal processing.
Nontrivial spectral properties of non-Hermitian systems can lead to intriguing effects with no counterparts in Hermitian systems. For instance, in a two-mode photonic system, by dynamically winding ...around an exceptional point (EP) a controlled asymmetric-symmetric mode switching can be realized. That is, the system can either end up in one of its eigenstates, regardless of the initial eigenmode, or it can switch between the two states on demand, by simply controlling the winding direction. However, for multimode systems with higher-order EPs or multiple low-order EPs, the situation can be more involved, and the ability to control asymmetric-symmetric mode switching can be impeded, due to the breakdown of adiabaticity. Here we demonstrate that this difficulty can be overcome by winding around exceptional curves by additionally crossing diabolic points. We consider a four-mode \(\cal PT\)-symmetric bosonic system as a platform for experimental realization of such a multimode switch. Our work provides alternative routes for light manipulations in non-Hermitian photonic setups.
The topological structure associated with the branchpoint singularity around an exceptional point (EP) can provide tools for controlling the propagation of light. Using graphene-based devices, we ...demonstrate the emergence of EPs in the electrically controlled interaction of light with a collection of organic molecules in the terahertz regime at room temperature. We show that the intensity and phase of terahertz pulses can be controlled by a gate voltage which drives the device across the EP. Our electrically tuneable system allows reconstructing the Riemann surface associated with the complex energy landscape and provides a topological control of light by tuning the loss-imbalance and frequency detuning of interacting modes. Our approach provides a platform for developing topological optoelectronics and studying the manifestations of EP physics in light-matter interactions.
Nonreciprocal interactions break action-reaction symmetry in systems of interacting bodies. This process inevitably introduces non-Hermitian dynamics which with its hallmark signature called ...exceptional points (EPs) has been a subject of intense research across different disciplines ranging from photonics to metamaterials. Whether non-Hermiticity and EPs are a fundamental property of nature and if so, how nature utilizes them to gain competitive advantage have remained largely unanswered. Although biological systems feature many examples of non-reciprocal interactions with the potential to drive non-Hermitian dynamics, these are often theoretically overlooked and not experimentally investigated. Here, we demonstrate in an active matter composed of social animal Caenorhabditis elegans and bacteria, non-Hermitian dynamics, and the emergence of EPs owing to the nonreciprocal nature of oxygen sensing, nonequilibrium interfacial current, and bacterial consumption. We observed that when driven through the EP, the system collectively breaks parity-time (PT) symmetry leading to traveling waves and arrested phase separation. We further find that these features enable the collective ability to localize interfaces between broken and exact PT-phases. Remarkably, this ability provides a strong evolutionary advantage to animals living in soil. Altogether our results provide mechanistic insights into the detailed symmetries controlling the collective response of biological systems; answer a long-standing problem; and give an example of the EP-enabled dynamics in a biological system.
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