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Symmetry-breaking-induced nonlinear optics at a microcavity surface

期刊: NATURE PHOTONICS, 2019; 13 (1)

Second-order nonlinear optical processes lie at the heart of many applications in both classical and quantum regimes(1-3). Inversion symmetry, however, rules out the second-order nonlinear electric-dipole response(1,4,5) in materials widely adopted in integrated photonics (for example, SiO2, Si and Si3N4). Here, we report nonlinear optics induced by symmetry breaking(6-10) at the surface of an ultrahigh-Q silica microcavity under a sub-milliwatt continuous-wave pump. By dynamically coordinating the double-resonance phase matching, a second harmonic is achieved with an unprecedented conversion efficiency of 0.049% W-1, 14 orders of magnitude higher than that of the non-enhancement case(11). In addition, the nonlinear effect from the intrinsic symmetry breaking at the surface(8,12) can be identified unambiguously, with guided control of the pump polarization and the recognition of the second-harmonic mode distribution. This work not only extends the emission frequency range of silica photonic devices, but also lays the groundwork for applications in ultra-sensitive surface analysis.

JIF:31.58

Entanglement of three quantum memories via interference of three single photons

期刊: NATURE PHOTONICS, 2019; 13 (3)

Quantum memory networks as an intermediate stage in the development of a quantum internet(1) will enable a number of significant applications(2-5). To connect and entangle remote quantum memories, it is best to use photons. In previous experiments(6-13), entanglement of two memory nodes has been achieved via photon interference. Going beyond the state of the art by entangling many quantum nodes at a distance is highly sought after. Here, we report the entanglement of three remote quantum memories via three-photon interference. We employ laser-cooled atomic ensembles and make use of a ring cavity to enhance the overall efficiency of our memory-photon entanglement. By interfering three single photons from three separate set-ups, we create entanglement of three memories and three photons. Then, by measuring the photons and applying feed-forward, we achieve heralded entanglement between the three memories. Our experiment may be employed as a building block to construct larger and complex quantum networks(14,15).

JIF:31.58

Strategies towards rational design of gold(III) complexes for high-performance organic light-emitting devices

期刊: NATURE PHOTONICS, 2019; 13 (3)

Gold(III) complexes are attractive candidates as phosphorescent dopants in organic light-emitting devices for high-luminance full-colour displays. However, no data on the stability of such devices have been reported to date. Through rational molecular design and synthesis, we have successfully generated a new class of cyclometalated gold(III) C<^>C<^>N complexes with tunable emission colours spanning from sky-blue to red. These complexes exhibit high photoluminescence quantum yields of up to 80% in solid-state thin films, excellent solubility and high thermal stability. Solution-processable and vacuum-deposited organic light-emitting devices based on these complexes operate with external quantum efficiencies of up to 11.9% and 21.6%, respectively, and operational half-lifetimes of up to 83,000 h at 100 cd m(-2).

JIF:31.58

Video-rate imaging of biological dynamics at centimetre scale and micrometre resolution

期刊: NATURE PHOTONICS, 2019; 13 (11)

Large-scale imaging of biological dynamics with high spatiotemporal resolution is indispensable to system biology studies. However, conventional microscopes have an inherent compromise between the achievable field of view and spatial resolution due to the space-bandwidth product theorem. In addition, a further challenge is the ability to handle the enormous amount of data generated by a large-scale imaging platform. Here, we break these bottlenecks by proposing the use of a flat-curved-flat imaging strategy, in which the sample plane is magnified onto a large spherical image surface and then seamlessly conjugated to multiple planar sensors. Our real-time, ultra-large-scale, high-resolution (RUSH) imaging platform operates with a 10 x 12 mm(2) field of view, a uniform resolution of similar to 1.20 mu m after deconvolution and a data throughput of 5.1gigapixels per second. We use the RUSH platform to perform video-rate, gigapixel imaging of biological dynamics at centimetre scale and micrometre resolution, including brain-wide structural imaging and functional imaging in awake, behaving mice.

JIF:31.58

Towards optimal single-photon sources from polarized microcavities

期刊: NATURE PHOTONICS, 2019; 13 (11)

An optimal single-photon source should deterministically deliver one, and only one, photon at a time, with no trade-off between the source's efficiency and the photon indistinguishability. However, all reported solid-state sources of indistinguishable single photons had to rely on polarization filtering, which reduced the efficiency by 50%, fundamentally limiting the scaling of photonic quantum technologies. Here, we overcome this long-standing challenge by coherently driving quantum dots deterministically coupled to polarization-selective Purcell microcavities. We present two examples: narrowband, elliptical micropillars and broadband, elliptical Bragg gratings. A polarization-orthogonal excitation-collection scheme is designed to minimize the polarization filtering loss under resonant excitation. We demonstrate a polarized single-photon efficiency of 0.60 +/- 0.02 (0.56 +/- 0.02), a single-photon purity of 0.975 +/- 0.005 (0.991 +/- 0.003) and an indistinguishability of 0.975 +/- 0.006 (0.951 +/- 0.005) for the micropillar (Bragg grating) device. Our work provides promising solutions for truly optimal single-photon sources combining near-unity indistinguishability and near-unity system efficiency simultaneously.

JIF:31.58

Efficient blue light-emitting diodes based on quantum-confined bromide perovskite nanostructures

期刊: NATURE PHOTONICS, 2019; 13 (11)

The emergence of inorganic-organic hybrid perovskites, a unique class of solution-processable crystalline semiconductors, provides new opportunities for large-area, low-cost and colour-saturated light-emitting diodes (LEDs) ideal for display and solid-state lighting applications(1). However, the performance of blue perovskite LEDs (PeLEDs)(2-11) is far inferior to that of their near-infrared, red and green counterparts(12-19), strongly limiting the practicality of the PeLED technology. Here, we demonstrate blue PeLEDs emitting at 483 nm with colour coordinates of (0.094, 0.184) and operating with a peak external quantum efficiency of up to 9.5% at a luminance of 54 cd m(-2). The devices have a T-50 lifetime of 250 s for an initial brightness of 100 cd m(-2). The efficient blue electroluminescence originates from a structure of quantum-confined perovskite nanoparticles embedded within quasi-two-dimensional phases with higher bandgaps, prepared by an antisolvent processing scheme. Our work paves the way towards high-performance PeLEDs in the blue region.

JIF:31.58

Graphene photonic crystal fibre with strong and tunable light-matter interaction

期刊: NATURE PHOTONICS, 2019; 13 (11)

The integration of photonic crystal fibre (PCF) with various functional materials has greatly expanded the application regimes of optical fibre(1-12). The emergence of graphene (Gr) has stimulated new opportunities when combined with PCF, allowing for electrical tunability, a broadband optical response and all-fibre integration ability(13-18). However, previous demonstrations have typically been limited to micrometre-sized samples, far behind the requirements of real applications at the metre-scale level. Here, we demonstrate a new hybrid material, Gr-PCF, with length up to half a metre, produced using a chemical vapour deposition method. The Gr-PCF shows a strong light-matter interaction with similar to 8 dB cm(-1) attenuation. In addition, the Gr-PCF-based electro-optic modulator demonstrates a broadband response (1,150-1,600 nm) and large modulation depth (similar to 20 dB cm(-1) at 1,550 nm) under a low gate voltage of similar to 2 V. Our results could enable industrial-level graphene applications based on this Gr-PCF and suggest an attractive platform for two-dimensional material-PCF.

JIF:31.58

Transverse photon spin of bulk electromagnetic waves in bianisotropic media

期刊: NATURE PHOTONICS, 2019; 13 (12)

Photons possess spin degree of freedom, which plays an important role in various applications such as optical communications, information processing and sensing. In isotropic media, photon spin is aligned with the propagation direction of light, obeying the principle of spin momentum locking. Interestingly, surface waves decaying away from an interface have a photon spin transverse to its propagation, opening exciting opportunities for the observation of spin-dependent excitation in confined systems. Here, we propose and realize transverse photon spin (T-spin) in a bulk medium, without relying on the presence of any interfaces. We show the mapping of the T-spin of surface modes to that of the bulk modes by introducing bianisotropy into the medium. We further discover that the interface between two bianisotropic media of opposite orientations supports edge-dependent propagating modes with tunable cutoff frequencies. Our results provide a new platform for manipulating the spin-orbit interaction of electromagnetic waves.

JIF:31.58

Quantum wave-particle superposition in a delayed-choice experiment

期刊: NATURE PHOTONICS, 2019; 13 (12)

Wave-particle duality epitomizes the counterintuitive character of quantum physics. A striking illustration is the quantum delayed-choice experiment, which is based on Wheeler's classic delayed-choice gedanken experiment, but with the addition of a quantum-controlled device enabling wave-to-particle transitions. Here, we realize a quantum delayed-choice experiment in which we control the wave and the particle states of photons and particularly the phase between them, thus directly establishing the created quantum nature of the wave-particle. We generate three-photon entangled states and inject one photon into a Mach-Zehnder interferometer embedded in a 186-m-long two-photon Hong-Ou-Mandel interferometer. The third photon is sent 141 m away from the interferometers and remotely prepares a two-photon quantum gate according to independent active choices under Einstein locality conditions. We realize transitions between wave and particle states in both classical and quantum scenarios, and therefore tests of the complementarity principle that go fundamentally beyond earlier implementations.

JIF:31.58

High-performance hybrid silicon and lithium niobate Mach-Zehnder modulators for 100 Gbit s(-1) and beyond

期刊: NATURE PHOTONICS, 2019; 13 (5)

Optical modulators are at the heart of optical communication links. Ideally, they should feature low loss, low drive voltage, large bandwidth, high linearity, compact footprint and low manufacturing cost. Unfortunately, these criteria have been achieved only on separate occasions. Based on a silicon and lithium niobate hybrid integration platform, we demonstrate Mach-Zehnder modulators that simultaneously fulfil these criteria. The presented device exhibits an insertion loss of 2.5 dB, voltage-length product of 2.2 V cm in single-drive push-pull operation, high linearity, electro-optic bandwidth of at least 70 GHz and modulation rates up to 112 Gbit s(-1). The high-performance modulator is realized by seamless integration of a high-contrast waveguide based on lithium niobate-a popular modulator material-with compact, low-loss silicon circuitry. The hybrid platform demonstrated here allows for the combination of 'best-in-breed' active and passive components, opening up new avenues for future high-speed, energy-efficient and cost-effective optical communication networks.

JIF:31.58

Efficient quantum memory for single-photon polarization qubits

期刊: NATURE PHOTONICS, 2019; 13 (5)

A quantum memory, for storing and retrieving flying photonic quantum states, is a key interface for realizing long-distance quantum communication and large-scale quantum computation. While many experimental schemes demonstrating high storage and retrieval efficiency have been performed with weak coherent light pulses, all quantum memories for true single photons achieved so far have efficiencies far below 50%, a threshold value for practical applications. Here, we report the demonstration of a quantum memory for single-photon polarization qubits with an efficiency of > 85% and a fidelity of > 99%, based on balanced two-channel electromagnetically induced transparency in laser-cooled rubidium atoms. For the single-channel quantum memory, the optimized efficiency for storing and retrieving single-photon temporal waveforms can be as high as 90.6%. This result pushes the photonic quantum memory closer to practical applications in quantum information processing.

JIF:31.58

Rational molecular passivation for high-performance perovskite light-emitting diodes

期刊: NATURE PHOTONICS, 2019; 13 (6)

A major efficiency limit for solution-processed perovskite optoelectronic devices, for example light-emitting diodes, is trap-mediated non-radiative losses. Defect passivation using organic molecules has been identified as an attractive approach to tackle this issue. However, implementation of this approach has been hindered by a lack of deep understanding of how the molecular structures influence the effectiveness of passivation. We show that the so far largely ignored hydrogen bonds play a critical role in affecting the passivation. By weakening the hydrogen bonding between the passivating functional moieties and the organic cation featuring in the perovskite, we significantly enhance the interaction with defect sites and minimize non-radiative recombination losses. Consequently, we achieve exceptionally high-performance near-infrared perovskite light-emitting diodes with a record external quantum efficiency of 21.6%. In addition, our passivated perovskite light-emitting diodes maintain a high external quantum efficiency of 20.1% and a wall-plug efficiency of 11.0% at a high current density of 200 mA cm(-2), making them more attractive than the most efficient organic and quantum-dot light-emitting diodes at high excitations.

JIF:31.58

Colour-tunable ultra-long organic phosphorescence of a single-component molecular crystal

期刊: NATURE PHOTONICS, 2019; 13 (6)

Materials exhibiting long-lived, persistent luminescence in the visible spectrum are useful for applications in the display, information encryption and bioimaging sectors(1-4). Herein, we report the development of several organic phosphors that provide colour-tunable, ultra-long organic phosphorescence (UOP). The emission colour can be tuned by varying the excitation wavelength, allowing dynamic colour tuning from the violet to the green part of the visible spectrum. Our experimental data reveal that these organic phosphors can have an ultra-long lifetime of 2.45 s and a maximum phosphorescence efficiency of 31.2%. Furthermore, we demonstrate the applications of colour-tunable UOP for use in a multicolour display and visual sensing of ultraviolet light in the range from 300 to 360 nm. The findings open the opportunity for the development of smart luminescent materials and sensors with dynamically controlled phosphorescence.

JIF:31.58

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