There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.

Topological Photonics

Bound states in the continuum (BICs) are waves that remain localized even though they coexist with a continuous spectrum of radiating waves that can carry energy away. Their very existence defies conventional wisdom. Although BICs were first proposed in quantum mechanics, they are a general wave phenomenon and have since been identified in electromagnetic waves, acoustic waves in air, water waves and elastic waves in solids. These states have been studied in a wide range of material systems, such as piezoelectric materials, dielectric photonic crystals, optical waveguides and fibres, quantum dots, graphene and topological insulators. In this Review, we describe recent developments in this field with an emphasis on the physical mechanisms that lead to BICs across seemingly very different materials and types of waves. We also discuss experimental realizations, existing applications and directions for future work. The fascinating wave phenomenon of ‘bound states in the continuum’ spans different material and wave systems, including electron, electromagnetic and mechanical waves. In this Review, we focus on the common physical mechanisms underlying these bound states, whilst also discussing recent experimental realizations, current applications and future opportunities for research.

Bound states in the continuum

Trapped atoms on photonic structures inspire many novel quantum devices for quantum information processing and quantum sensing. Here, we have demonstrated a hybrid photonic-atom chip platform based on a GaN-on-sapphire chip and the transport of an ensemble of atoms from free space towards the chip with an optical conveyor belt. The maximum transport efficiency of atoms is about 50% with a transport distance of 500 $\mathrm{\mu m}$. Our results open up a new route toward the efficiently loading of cold atoms into the evanescent-field trap formed by the photonic integrated circuits, which promises strong and controllable interactions between single atoms and single photons.

Transporting cold atoms towards a GaN-on-sapphire chip via an optical conveyor belt

An integrated photonic device for converting on-chip waveguide modes to free-space optical angular momentum beams is proposed, which is composed of a polarization splitter rotator and a waveguide surface holographic grating. The output orbital angular momentum (OAM) state can be manipulated by the input polarization state. Therefore, the superposition of OAM states can be realized by controlling the on-chip input. According to the numerical results, the conversion efficiency of the transverse-magnetic (transverse-electric) mode to the optical angular momentum mode with [Formula: see text] is above 14% (18%), with the highest fidelity up to 0.84 and a working bandwidth of approximately 40 nm for a fidelity above 0.8. The proposed device provides a feasible information channel between the integrated optics and the free space and holds the potential for applications including the on-chip detection of the optical angular momentum beam.

On-chip converter of waveguide polarization mode to free-space optical angular momentum mode

We experimentally report a novel asymmetrical spherical microcavity with thermal-induced deformation, in which whispering gallery modes possess not only ultra-high quality factors (Q) but also remarkably directional escape emission from the microsphere boundary.

Inherently directional lasing from a thermal-induced-deformation high-Q microcavity

With the coupled-mode theory, we analyzed the energy transmission between the microsphere cavity and waveguide system, and revealed the mode coupling strength in a bare microsphere coupled with a fiber taper theoretically and experimentally. In a practical taper-microsphere coupling system, the traveling wave clockwise (CW) and counterclockwise (CCW) whispering gallery modes (WGMs) should existed simultaneity. Those two modes are coupled in the microsphere cavity with a coupling strength (beta). In experiment, the reflection spectra of the taper-microsphere system were investigated, By modifying various coupling condition for microspheres, different groups of data were obtained from the spectra, and used as fitting data for coupling strength estimation. The theory will be valuable in evaluating the upper limit of quality factor (Q) of a microcavity basing on the WGMs. Referring to the result and consequence of beta, it enables multiple ways to improve the Q-factor of a real cavity like annealing. Because the experiment device is compact and sensitive, such method is also promising for detecting the propagating loss in fiber instead of traditional way.

Mode coupling strength in a microsphere cavity coupled with fiber taper

Optical bistability (OB) of Rydberg atoms provides a new, to the best of our knowledge, platform for studying nonequilibrium physics and a potential resource for precision metrology. To date, the observation of Rydberg OB has been limited in free space. Here, we explore cavity-enhanced Rydberg OB with a thermal cesium vapor cell. The signal of Rydberg OB in a cavity is enhanced by more than one order of magnitude compared with that in free space. The slope of the phase transition signal at the critical point is enhanced more than 10 times that without the cavity, implying an enhancement of two orders of magnitude in the sensitivity for Rydberg-based sensing and metrology.

Chang-Ling Zou

Papers

Transporting cold atoms towards a GaN-on-sapphire chip via an optical conveyor belt

On-chip converter of waveguide polarization mode to free-space optical angular momentum mode

Inherently directional lasing from a thermal-induced-deformation high-Q microcavity

Mode coupling strength in a microsphere cavity coupled with fiber taper

Cavity-enhanced optical bistability of Rydberg atoms.