Exploiting the interplay between gain, loss and the coupling strength between different optical components creates a variety of new opportunities in photonics to generate, control and transmit light. ...Inspired by the discovery of real eigenfrequencies for non-Hermitian Hamiltonians obeying parity–time (PT) symmetry, many counterintuitive aspects are being explored, particularly close to the associated degeneracies also known as ‘exceptional points’. This Review explains the underlying physical principles and discusses the progress in the experimental investigation of PT-symmetric photonic systems. We highlight the role of PT symmetry and non-Hermitian dynamics for synthesizing and controlling the flow of light in optical structures and provide a roadmap for future studies and potential applications.This Review discusses recent developments in the area of non-Hermitian physics, and more specifically the special case of non-Hermitian optical systems with parity–time symmetry.
Engineering light-matter interactions using non-Hermiticity, particularly through spectral degeneracies known as exceptional points (EPs), is an emerging field with potential applications in areas ...such as cavity quantum electrodynamics, spectral filtering, sensing, and thermal imaging. However, tuning and stabilizing a system to a discrete EP in parameter space is a challenging task. Here, we circumvent this challenge by operating a waveguide-coupled resonator on a surface of EPs, known as an exceptional surface (ES). We achieve this by terminating only one end of the waveguide with a tuneable symmetric reflector to induce a nonreciprocal coupling between the frequency-degenerate clockwise and counterclockwise resonator modes. By operating the system at critical coupling on the ES, we demonstrate chiral and degenerate perfect absorption with squared-Lorentzian lineshape. We expect our approach to be useful for studying quantum processes at EPs and to serve as a bridge between non-Hermitian physics and other fields that rely on radiation engineering.
Loss-induced suppression and revival of lasing Peng, B.; Özdemir, Ş. K.; Rotter, S. ...
Science (American Association for the Advancement of Science),
10/2014, Letnik:
346, Številka:
6207
Journal Article
Recenzirano
Odprti dostop
Controlling and reversing the effects of loss are major challenges in optical systems. For lasers, losses need to be overcome by a sufficient amount of gain to reach the lasing threshold. In this ...work, we show how to turn losses into gain by steering the parameters of a system to the vicinity of an exceptional point (EP), which occurs when the eigenvalues and the corresponding eigenstates of a system coalesce. In our system of coupled microresonators, EPs are manifested as the loss-induced suppression and revival of lasing. Below a critical value, adding loss annihilates an existing Raman laser. Beyond this critical threshold, lasing recovers despite the increasing loss, in stark contrast to what would be expected from conventional laser theory. Our results exemplify the counterintuitive features of EPs and present an innovative method for reversing the effect of loss.
When two resonant modes in a system with gain or loss coalesce in both their resonance position and their width, a so-called exceptional point occurs, which acts as a source of non-trivial physics in ...a diverse range of systems. Lasers provide a natural setting to study such non-Hermitian degeneracies, as they feature resonant modes and a gain material as their basic constituents. Here we show that exceptional points can be conveniently induced in a photonic molecule laser by a suitable variation of the applied pump. Using a pair of coupled microdisk quantum cascade lasers, we demonstrate that in the vicinity of these exceptional points the coupled laser shows a characteristic reversal of its pump dependence, including a strongly decreasing intensity of the emitted laser light for increasing pump power.
The suicide rate in the U.S. has been increasing in recent years. Previous studies have consistently identified financial stress as a contributing factor in suicides. Nevertheless, there has been ...little research on the effect of economic policies that can alleviate financial stress on suicide rates. The purpose of this study is to determine whether increases in state minimum wages have been associated with changes in state suicide rates.
A retrospective panel data study was conducted. In 2018, linear regression models with state fixed effects were used to estimate the relationship between changes in state minimum wages and suicide rates for all 50U.S. states between 2006 and 2016. Models controlled for time-varying state characteristics that could be associated with changes in minimum wages and suicide rates.
There were approximately 432,000 deaths by suicide in the study period. A one-dollar increase in the real minimum wage was associated on average with a 1.9% decrease in the annual state suicide rate in adjusted analyses. This negative association was most consistent in years since 2011. An annual decrease of 1.9% in the suicide rate during the study period would have resulted in roughly 8,000 fewer deaths by suicide. Analyses by race and sex did not reveal substantial variation in the association between minimum wages and suicides.
Increases in real minimum wages have been associated with slower growth in state suicide rates in recent years. Increasing the minimum wage could represent a strategy for addressing increases in suicide rates.
Hybridized systems offer a promising route for developing quantum devices, but inhomogeneous broadening limits the practical use of large spin ensembles. Suppression of the decoherence induced by ...such broadening has now been demonstrated for a superconducting cavity coupled to an ensemble of nitrogen-vacancy centres in diamond.
In all of the diverse areas of science where waves play an important role, one of the most fundamental solutions of the corresponding wave equation is a stationary wave with constant intensity. The ...most familiar example is that of a plane wave propagating in free space. In the presence of any Hermitian potential, a wave's constant intensity is, however, immediately destroyed due to scattering. Here we show that this fundamental restriction is conveniently lifted when working with non-Hermitian potentials. In particular, we present a whole class of waves that have constant intensity in the presence of linear as well as of nonlinear inhomogeneous media with gain and loss. These solutions allow us to study the fundamental phenomenon of modulation instability in an inhomogeneous environment. Our results pose a new challenge for the experiments on non-Hermitian scattering that have recently been put forward.
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