Probing Complex-energy Topology via Non-Hermitian Absorption Spectroscopy in a Trapped Ion Simulator

Non-Hermitian systems generically have complex energies, which may host topological structures, such as links or knots. While there has been great progress in experimentally engineering non-Hermitian models in quantum simulators, it remains a significant challenge to experimentally probe complex energies in these systems, thereby making it difficult to directly diagnose complex-energy topology. Here, we experimentally realize a two-band non-Hermitian model with a single trapped ion whose complex eigenenergies exhibit the unlink, unknot or Hopf link topological structures. Based on non-Hermitian absorption spectroscopy, we couple one system level to an auxiliary level through a laser beam and then experimentally measure the population of the ion on the auxiliary level after a long period of time. Complex eigenenergies are then extracted, illustrating the unlink, unknot or Hopf link topological structure. Our work demonstrates that complex energies can be experimentally measured in quantum simulators via non-Hermitian absorption spectroscopy, thereby opening the door for exploring various complex-energy properties in non-Hermitian quantum systems, such as trapped ions, cold atoms, superconducting circuits or solid-state spin systems.Comment: 12 pages, 8 figure

Optical heterodyne micro-vibration detection based on all-fiber acousto-optic superlattice modulation

We propose a configuration of optical heterodyne micro-vibration detection based on an all-fiber acousto-optic superlattic modulation structure that acts as both frequency shifter and reflector, simultaneously. The vibration information within the frequency range between 1 Hz to 150 kHz of a piezoelectric mirror (PZM) has been experimentally measured by using this all-fiber optical heterodyne detection configuration. The minimal measurable vibration amplitude and the resolution are around 0.013 nm and 10 pm in the region of tens to hundreds of kilohertz, respectively. The configuration not only has advantages of compact size, easy alignment and non-contact measurement, but also gains high accuracy, which provides a promising alternative and could be applied in the compact and portable instruments based on optical heterodyne detection

SoccerNet 2023 Challenges Results

peer reviewedThe SoccerNet 2023 challenges were the third annual video understanding challenges organized by the SoccerNet team. For this third edition, the challenges were composed of seven vision-based tasks split into three main themes. The first theme, broadcast video understanding, is composed of three high-level tasks related to describing events occurring in the video broadcasts: (1) action spotting, focusing on retrieving all timestamps related to global actions in soccer, (2) ball action spotting, focusing on retrieving all timestamps related to the soccer ball change of state, and (3) dense video captioning, focusing on describing the broadcast with natural language and anchored timestamps. The second theme, field understanding, relates to the single task of (4) camera calibration, focusing on retrieving the intrinsic and extrinsic camera parameters from images. The third and last theme, player understanding, is composed of three low-level tasks related to extracting information about the players: (5) re-identification, focusing on retrieving the same players across multiple views, (6) multiple object tracking, focusing on tracking players and the ball through unedited video streams, and (7) jersey number recognition, focusing on recognizing the jersey number of players from tracklets. Compared to the previous editions of the SoccerNet challenges, tasks (2-3-7) are novel, including new annotations and data, task (4) was enhanced with more data and annotations, and task (6) now focuses on end-to-end approaches. More information on the tasks, challenges, and leaderboards are available on https://www.soccer-net.org. Baselines and development kits can be found on https://github.com/SoccerNet

Construction and testing of the China's labor marketization index

In this paper we used two primary indicators and four secondary indicators to construct China's labor marketization index. We calculated the index at the prefecture-level cities from 2010 to 2016 and tested its correlation with macroeconomic indicators. The results show that there has been much progress in labor marketization in China over the period, and the key to this progress is the quantity factor rather than the price factor. Progress in labor marketization varies considerably across regions and at different levels of cities. The external validity test confirms that this index has a strong scientific basis

Ultrafast all-fiber based cylindrical-vector beam laser

Cylindrical-vector beams (CVBs) with axial symmetry in polarization and field intensity are gathering increasing attention from fundamental research to practical applications. However, a majority of the CVBs are generated by modulating light beams in free space, and the temporal durations are far away from the ultrafast regime. Here, an ultrafast all-fiber based CVB laser is demonstrated via intermodal coupling in two mode fibers. In the temporal domain, chirp-free pulses are formed with combined actions of the ultrafast saturable absorption, self-phase modulation, and anomalous dispersion. In the spatial domain, the lateral offset splicing technique and a two mode fiber Bragg grating are adopted to excite and extract CVBs, respectively. The ultrafast CVB has an annular profile with a duration of 6.87 ps and a fundamental repetition rate of 13.16 MHz, and the output polarization status is switchable between radially and azimuthally polarized states. This all-fiber-based ultrafast CVB laser is a simple, low-cost source for diversified applications of nanoparticle manipulation, high-resolution imaging, material processing, spatiotemporal nonlinear optics, etc.Peer reviewe

Highly efficient plasmonic nanofocusing on a metallized fiber tip with internal illumination of the radial vector mode using an acousto-optic coupling approach

Tip-based plasmonic nanofocusing, which delivers light into a nanoscale region and achieves localized electromagnetic (EM) field enhancement beyond the diffraction limit, is highly desired for light-matter interaction-based super-resolution imaging. Here, we present the plasmonic nanofocusing at the apex of a silver (Ag)-coated fiber tip with the internal illumination of a radial vector mode (RVM) generated directly in an optical fiber based on an acoustically-induced fiber grating (AIFG). As illustrated by theoretical calculation, a picture of the nanofocusing plasmonic tip given by analyzing the mode conversion process that the surface plasmon polariton (SPP) mode excited via the radial polarization optical mode can propagate to the apex of the plasmonic tip for nanofocusing because it is not cut off as the tip radius decreases; while the SPP mode which transited from the linear polarization optical mode cannot propagate to the tip apex for nanofocusing because it is cut off as the tip radius decreases. The electric field intensity enhancement factor |Eapex2|/|Einput2|$|{\rm{E}}_{{\rm{apex}}}^{\rm{2}}|/|{\rm{E}}_{{\rm{input}}}^{\rm{2}}|$ of a plasmonic tip with a tip radius of 20 nm was calculated to be ~2 × 103. Furthermore, the electric field enhancement characteristic at the tip apex was also experimentally verified by using surface-enhanced Raman spectroscopy (SERS). The Raman scattering intensity was observed to be ~15 times as strong as that with internal illumination using the linear polarization mode (LPM), revealing their significantly different nanofocusing characteristics. A Raman sensitivity of 10−14m was achieved for the target analyte of malachite green (MG), denoting significant electric field enhancement and effective plasmonic nanofocusing. The energy conversion efficiency of the radial polarization optical mode to the corresponding SPP mode at the tip apex was measured to be ~17%. This light delivery technique can be potentially further exploited in near-field microscopy with improved resolution and conversion efficiency

Physical vapor deposition of large-scale PbSe films and its applications in pulsed fiber lasers

Lead selenide (PbSe) is a new emerging semiconductor with layer-dependent bandgap that has attracted much interest due to its high infrared response and good environmental stability. We have prepared large-scale PbSe films with the area of 7 cm2 and thickness of 25 nm based on physical vapor deposition approach at 160°C. The PbSe films exhibit saturable absorption property at 1.55 μm and a polarization-sensitive saturable absorber is obtained by growing PbSe on D-shaped fiber. Single-pulse with the duration of 490 fs is generated at the pump of 12 mW and the mode-locking operation is maintained at the pump of 1500 mW, indicating the high damage threshold of the D-shaped fiber based saturable absorber. Two polarization-insensitive saturable absorbers are achieved by depositing PbSe on fiber facet and polyvinyl alcohol film, respectively. For fiber facet (polyvinyl alcohol film) based saturable absorber, the repetition rate of Q-switched pulses increases from 8.6 (16.3) kHz to 45.4 (59.2) kHz while the duration decreases from 7.92 (12) μs to 2.06 (3.12) μs by tuning the pump from 15 mW to 90 (60) mW. Such large-scale PbSe films possess features of low cost and high modulation ability, and can find important applications in infrared optical modulators and detectors