Integrated photonics platforms are a key driver for advancing scalable photonics technologies. To rigorously characterize and calibrate on-chip integrated photodetectors for ultra-sensitive applications such as quantum sensing and photonic computing, a low-power calibration source down to single-photon levels is required. To date, such sources still largely rely on off-chip bulk or fiber optic setups to accurately attenuate a laser beam referenced to a sub-mW-level primary standard. Here, we demonstrate an on-chip integrated attenuation solution where a mW-level beam is coupled to a silicon nitride photonics circuit, and is attenuated by a series of cascaded directional couplers (DCs). With an integrated silicon photodetector, we measured an attenuation at 685 nm wavelength of up to 16.61 dB with an expanded uncertainty of 0.24 dB for one DC stage. With appropriate scattering mitigation, we infer from our results that a total attenuation of 149.5 dB (expanded uncertainty of 0.5 dB) can be obtained with 9 stages of cascaded DCs, thus allowing single-photon power levels to be obtained directly on-chip from a moderate-power laser source.
Integration of single-photon emitters (SPEs) with resonant photonic structures is a promising approach for realizing compact and efficient single-photon sources for quantum communications, computing, and sensing. Efficient interaction between the SPE and the photonic cavity requires that the cavity's resonance matches the SPE's emission line. Here we demonstrate a new method for tuning silicon nitride (Si3N4) microring cavities via controlled deposition of the cladding layers. Guided by numerical simulations, we deposit silicon dioxide (SiO2) nanolayers onto Si3N4 ridge structures in steps of 50 nm. We show tuning of the cavity resonance exceeding a free spectral range (FSR) of 3.5 nm without degradation of the quality-factor (Q-factor) of the cavity. We then complement this method with localized laser heating for fine-tuning of the cavity. Finally, we verify that the cladding deposition does not alter the position and spectral properties of nanoparticles placed on the cavity, which suggests that our method can be useful for integrating SPEs with photonic structures.
Integrated photodetectors are essential components of scalable photonics platforms for quantum and classical applications. However, most efforts in the development of such devices to date have been focused on infrared telecommunications wavelengths. Here, we report the first monolithically integrated avalanche photodetector (APD) for visible light. Our devices are based on a doped silicon rib waveguide with a novel end-fire input coupling to a silicon nitride waveguide. We demonstrate a high gain-bandwidth product of 234 ± 25 GHz at 20 V reverse bias measured for 685 nm input light, with a low dark current of 0.12 µA. We also observe open eye diagrams at up to 56 Gbps. This performance is very competitive when benchmarked against other integrated APDs operating in the infrared range. With CMOS-compatible fabrication and integrability with silicon photonic platforms, our devices are attractive for sensing, imaging, communications, and quantum applications at visible wavelengths.
Replacing flammable organic electrolytes with aqueous electrolytes in lithium-ion batteries (LIB) can greatly enhance the safety of next-generation energy storage systems. With the extended electrochemical stability window of electrolytes, 'water-in-salt' (WIS) electrolytes containing LIB presented significant performance improvements. However, the solubility limits of lithium salts in water restrain the extent of kinetic protection offered by the high salt concentration. Here, we report design strategies of anode structure to improve the cycle life of LIB with WIS electrolytes. We introduced partially graphitic protective carbon layers on anode particles using a versatile coating method. This protective layer not only improved charge transfer kinetics but also minimized the exposure of anode surface for water electrolysis. The effectiveness of anode structure developed in this study was exemplified on TiO2 anodes, where cycle performance and coulombic efficiency improved by 11 times and 29% respectively over the base anode material.
Intracystic papillary carcinoma of the breast is a rare subtype of breast cancer accounting for approximately 0.5-1% of all breast carcinomas. To the best of our knowledge, the occurrence of this rare subtype of breast cancer in the male is even lower with less than 20 cases reported in the English literature over the past 30 years. We report a case of an elderly Asian male with intracystic papillary breast carcinoma who initially presented with a right sided breast lump for 4 months duration and his subsequent management. In addition, a review of similar cases in the English literature is included.
Integrated photonics platforms are crucial to the development and implementation of scalable quantum information and networking schemes, but many such devices still rely on external bulk photodetectors. We report the design and simulation of a waveguide-based single-photon avalanche diode (SPAD) for visible wavelengths. The SPAD consists of a p-n junction implemented in a doped silicon waveguide, which is end-fire coupled to an input silicon nitride waveguide. We developed a 2D Monte Carlo model to simulate the avalanche multiplication process of charge carriers following the absorption of an input photon, and calculated the photon detection efficiency (PDE) and timing jitter of the SPAD. We investigated the SPAD performance at a wavelength of 640 nm and temperature of 243K for different device dimensions and device doping configurations. For our simulated parameters, we obtained a maximum PDE of 0.45 at a reverse bias voltage of ~20 V, and full-width-half-max (FWHM) timing jitter values <8 ps.
Nanodidamonds containing colour centres open up many applications in quantum information processing, metrology, and quantum sensing. However, controlling the synthesis of nanodiamonds containing silicon vacancy (SiV) centres is still not well understood. Here we study nanodiamonds produced by a high-pressure high-temperature method without catalyst metals, focusing on two samples with clear SiV signatures. Different growth temperatures and relative content of silicon in the initial compound between the samples altered their nanodiamond size distributions and abundance of SiV centres. Our results show that nanodiamond growth can be controlled and optimised for different applications.
The numerical aperture (NA) of a lens determines its ability to focus light and its resolving capability. Having a large NA is a very desirable quality for applications requiring small light-matter interaction volumes or large angular collections. Traditionally, a large NA lens based on light refraction requires precision bulk optics that ends up being expensive and is thus also a specialty item. In contrast, metasurfaces allow the lens designer to circumvent those issues producing high-NA lenses in an ultraflat fashion. However, so far, these have been limited to numerical apertures on the same order of magnitude as traditional optical components, with experimentally reported NA values of <0.9. Here we demonstrate, both numerically and experimentally, a new approach that results in a diffraction-limited flat lens with a near-unity numerical aperture (NA > 0.99) and subwavelength thickness (â¼λ/3), operating with unpolarized light at 715 nm. To demonstrate its imaging capability, the designed lens is applied in a confocal configuration to map color centers in subdiffractive diamond nanocrystals. This work, based on diffractive elements that can efficiently bend light at angles as large as 82°, represents a step beyond traditional optical elements and existing flat optics, circumventing the efficiency drop associated with the standard, phase mapping approach.
We investigate the scattering of single photons by single atoms and, in particular, the dependence of the atomic dynamics and the scattering probability on the photon bandwidth. We tightly focus the incident photons onto a single trapped 87Rb atom and use the time-resolved transmission to characterize the interaction strength. Decreasing the bandwidth of the single photons from 6 to 2 times the atomic linewidth, we observe an increase in atomic peak excitation and photon scattering probability.
Scattering of light by matter has been studied extensively in the past. Yet, the most fundamental process, the scattering of a single photon by a single atom, is largely unexplored. One prominent prediction of quantum optics is the deterministic absorption of a travelling photon by a single atom, provided the photon waveform matches spatially and temporally the time-reversed version of a spontaneously emitted photon. Here we experimentally address this prediction and investigate the influence of the photon's temporal profile on the scattering dynamics using a single trapped atom and heralded single photons. In a time-resolved measurement of atomic excitation we find a 56(11)% increase of the peak excitation by photons with an exponentially rising profile compared with a decaying one. However, the overall scattering probability remains unchanged within the experimental uncertainties. Our results demonstrate that envelope tailoring of single photons enables precise control of the photon-atom interaction.
Paraneoplastic syndromes are rare first manifestations of breast cancer. In this report, we present two cases of a 58-year-old woman and a 69-year-old woman presenting with acute symptoms of paraneoplastic cerebellar degeneration (PCD) and dermatomyositis, respectively, as the first sign of breast malignancy. The patient diagnosed with PCD presented initially with ataxia, was serum anti-Yo antibody negative, and subsequently investigated to have poorly differentiated intraductal breast carcinoma. Cerebellar symptoms regressed following breast cancer surgery and chemotherapy, highlighting the better neurological prognosis associated with anti-Yo antibody negative PCD. The rarity of these presentations highlights the necessity to include an occult malignancy in the differential diagnosis when attending to such patients.
