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Matching media are located between wearable antennas and the human body to enhance implant communications. The selection of the matching medium is a complicated problem, and there is yet no well-established approach. The simulations are computationally expensive, and the theoretical work is limited. Hence, this work proposes a novel approach by using artificial neural networks for determining the effect of various matching media. For this aim, a wearable repeater antenna, human tissue blocks with varying relative permittivities, and matching medium layer with varying relative permittivities and thicknesses are utilized. Employing more than 200 simulated designs, optimum matching medium designs are proposed, and the matching medium concept has been shown to increase the average transmitted power by 17.6%. Moreover, it is shown that the trained neural network model can predict the test cases with 4.5% mean error and the computational cost has been decreased by 91% compared to the empirical method.

In cellular communication systems, the distance from base station to subscriber equipment is limited. In cases where this distance cannot be reduced, it is suggested to introduce a repeater using a location detection method, such as GPS, to increase the range. The distance between the nearest base station and the repeater maybe calculated by determining the coordinates of the repeater and the base station. By increasing the power of both the repeater and the base station transmitters, and changing the time advance, the repeater may be connected to the base station. The connection between the subscriber terminal and the base station is facilitated through the repeater

With the rapid development of integrated nanophotonics technology, the circuit architecture for optical neural networks that construct neural networks based on integrated nanophotonics has been widely investigated. Since the optical neural network can complete the inference processing just by propagating the optical signal in the network, the inference processing by the optical neural network is expected more than one order of magnitude faster than the electronics-only implementation of an artificial neural network (ANN). In this paper, we first propose an optical vector-matrix multiplication (VMM) circuit using wavelength division multiplexing, which enables inference processing with ultra-wideband. Although the optical VMM circuit is extremely fast, the initial version is designed for fully connected network structures, which consume large amounts of power in laser light sources. As a solution to this power explosion, this paper especially proposes sparsely connected network structures for the optical VMM operation, which reduces the power consumed in the laser sources by three orders of magnitude without any speed and bandwidth degradation compared with the fully connected counterpart. Although the main part of ultra-fast ANN is VMM, batch normalization and activation function are integral parts for accurate inference processing in ANN. Batch normalization applied at inference processing is a technique for improving the inference accuracy of ANN. Without batch normalization and activation function, the inference accuracy of ANN may significantly degrade. In this paper, we next propose electronic circuit implementation of batch normalization and activation function, which significantly improves the accuracy of inference processing without sacrificing the speed performance of inference processing. Those two functions can be implemented based on an energy-efficient O-E-O repeater circuit. We specifically propose the electronic implementation of Exponential Linear Unit (ELU in short) as an activation function. It is known that ELU largely contributes to improving the inference accuracy of ANN as well as learning speed. Finally, in this paper, we demonstrate the ultra-fast and accurate operation of the optical-electronic ANN circuit using TensorFlow and optoelectronic circuit simulator.

In this paper, the use of a repeater element between the transmitter and the receiver of a capacitive wireless power transfer system for achieving larger transfer distances is analyzed. A network formalism is adopted and the performance described by using the three power gains usually adopted in the context of two-port active networks. The analytical expressions of the gains as function of the network elements are derived. Assuming that the parameters of the link are given and fixed, including the coupling factors between transmitter, repeater and receiver, the conditions for maximizing the different gains by acting on the network terminating impedances (i.e., load and internal source conductance) are determined. The analytical formulas are verified through circuital simulations.

The article shows the results of modeling the electrical circuits of integrated sensor as part of the CMOS inverter. Capacitor, inductor and MOS transistor were used as the integrated sensor. The change of sensor values is detected by a circuit containing three stages: input buffer, amplifier and repeater. The integral sensor is connected to the gate of one of the MOS transistors of input buffer. Shows how the change in the value of the integrated sensor affects the shape of the output signal of the measuring circuit

The increase in the throughput of digital television and radio broadcasting (DVB) channels can be achieved due to application of signals with a compact spectrum and a relatively small peak-to-average power ratio (PAPR). The reason is the usage of traveling wave tubes (TWT) for amplifying and transmitting signals from a satellite repeater in DVB-S2X systems. At the same time, given that the bandwidth allocated for transmission should be used as efficiently as possible, a high reduction rate of out-of-band emissions level is required. The most effective solution in this direction is the transition to spectrum-economic signals, such as optimal Faster-Than-Nyquist (FTN) signals, which can provide a certain reduction rate of the out-of-band emissions level and minimum acceptable PAPR. This article proposes a method for obtaining optimal FTN pulses, which have symmetry in time domain, with specified PAPR and reduction rate of out-of-band emissions for the quadrature phase shift keying (QPSK) and offset quadrature phase shift keying (OQPSK). The possibility of synthesizing signals with OQPSK modulation is presented theoretically for the first time. Optimal FTN signals can provide PAPR reduction by at most 3 dB and outperform known root raised cosine (RRC) pulses. The simulation model adopts an architecture for quadrature generation of optimal FTN signals with OQPSK modulation with blocks for adjustable pre-amplification, clipping, and power amplification. The proposed signals can be used to increase the spectral and energy efficiencies of satellite broadcasting systems, such as DVB-S2/S2X, as well as low-rate return channels of interactive broadcasting systems with a frequency resource shortage.

We introduce multi-branch repeater laser stations (MLSs) for the dissemination of an ultra-stable signal from one point to multiple users and the simultaneous evaluation of the stability and accuracy of multiple links. We perform the study of the noise floor of this new instrument. We present then an optical fiber network of 4800 km built with three MLSs and 13 repeater laser stations (RLSs). We show the multi-user optical frequency dissemination on four links totalizing 2198 km with uncertainties below 1.1 × 10−19. The robustness of the network over two years is presented and stability and accuracy at 107 seconds integration time are finally showed.

Reduction in base-station deployment costs while increasing coverage has motivated Integrated Access and Backhaul (IAB) nodes in mm-wave 5G NR (Fig. 14.3.1). Similarly, high path loss due to shadowing and limited outdoor-to-indoor penetration at mm-wave has led to an interest in repeater/relays to extend 5G NR coverage [1]. Currently, halfduplexlinks based on TDD (preferred for lAB), FDD, spatial, and polarization-duplexare explored, targeting mm-wave TWRX isolation at the cost of channel capacity. While mmwave in-band full-duplex (IBFD) with shared antenna (ANT) interface can enable spectrum reuse in IAB and repeaters/relays, >100dB total self-interference cancellation (SIC) is required with up to 50dB of SIC in the mm-wave front-end [2]. Such SIC has been shown for IBFD at RF [3– 5], however mm-wave IBFD SIC with a shared antenna interface has been limited to 20dBat28GHz and 40dB(22dB at +10dBm TX SI power) at 60GHz [6, 7]. Achieving mm-wave IBFD SIC with a shared ANT interface is particularly challenging given (i) the high frequency of operation, (ii) wide 400MHz/800MHz bandwidths targeted in 5G NR, and (iii) variations in beamformer ANT impedance that changes the SI channel. This paper presents a fully integrated mm-wave circulator RX that addresses these challenges using (i) a hybrid-coupler and non-reciprocal N-path filter-based shared ANT interface that provides wideband SIC while creating an SI replica, enabling (ii) subsequent active cancellation with variable gain/phase shift to accommodate SI channel variations. The circulator RX implementation in 45nm SOI CMOS achieves 52. 8dB cancellation across 400MHz at 26. 4GHz(>100 $\times$ improvement over state of the art at high power levels) with 3.1dB TX-to-ANT insertion loss (IL) and +11.5dBm TX power-handling. System-level feasibility for mm-wave wideband IBFD is shown with the integrated RX supporting 600MS/s128-OAM wireless reception (4.2Gb/s) with 3.3% RX EVM in the presence of an in-band 128-OAM 300MS/s (limited by instrument) TX SI signal, and SIC is demonstrated across SI channel changes using a global optimization approach.

Long haul optical links provides the backbone for most of today's communication and the Internet in general. The throughput of an optical link witnessed a major breakthrough with the advent of optical amplifiers in the early 1990s. These optical amplifiers with their large bandwidth facilitated the introduction of Wavelength Division Multiplexing (WDM) and a bandwidth explosion followed. Though they provide good gain and large bandwidth, all while keeping the information in optical domain; optical amplifiers do add noise of its own to the data, which when cascaded over long distances starts to limit the link length. Optical-Electrical-Optical (OEO) regenerators are used to clean and regenerate the signal but are expensive and adds potential delays in the link. In this paper we investigates their theoretical performance differences and highlights the advantages of all regenerators link over all repeaters ones. We undertake this analytical study to investigate the absolute theoretical gains of implementing an all regenerator link which is to serve as a baseline, or a precursor, for further investigations on the advantages of all optical regenerative link. Here we derive the performance limits of an all regenerator systems and compare it with its amplifier/repeater counterparts. Noise evolution in all repeater links and BER accumulation for both are illustrated. We illustrate general optical link BER curves and compare all repeater/regenerator link performances against input power for single and multiple hops. We also translate the BER advantage of all regenerator link to longer link reaches or lower power requirements. The later is repeated for different target BER too.

Owing to the inevitable loss in communication channels, the distance of entanglement distribution is limited to approximately 100 kilometres on the ground. Quantum repeaters can circumvent this problem by using quantum memory and entanglement swapping. As the elementary link of a quantum repeater, the heralded distribution of two-party entanglement between two remote nodes has only been realized with built-in-type quantum memories. These schemes suffer from the trade-off between multiplexing capacity and deterministic properties and hence hinder the development of efficient quantum repeaters. Quantum repeaters based on absorptive quantum memories can overcome such limitations because they separate the quantum memories and the quantum light sources. Here we present an experimental demonstration of heralded entanglement between absorptive quantum memories. We build two nodes separated by 3.5 metres, each containing a polarization-entangled photon-pair source and a solid-state quantum memory with bandwidth up to 1 gigahertz. A joint Bell-state measurement in the middle station heralds the successful distribution of maximally entangled states between the two quantum memories with a fidelity of 80.4 $\pm$ 2.2 per cent ($\pm$1 standard deviation). The quantum nodes and channels demonstrated here can serve as an elementary link of a quantum repeater. Moreover, the wideband absorptive quantum memories used in the nodes are compatible with deterministic entanglement sources and can simultaneously support multiplexing, which paves the way for the construction of practical solid-state quantum repeaters and high-speed quantum networks., 36 pages, 11 figures

High-quality long-distance entanglement is essential for both quantum communication and scalable quantum networks. Entanglement purification is to distill high-quality entanglement from low-quality entanglement in a noisy environment and it plays a key role in quantum repeaters. The previous significant entanglement purification experiments require two pairs of low-quality entangled states and were demonstrated in table-top. Here we propose and report a high-efficiency and long-distance entanglement purification using only one pair of hyperentangled states. We also demonstrate its practical application in entanglement-based quantum key distribution (QKD). One pair of polarization spatial-mode hyperentanglement was distributed over 11 km multicore fiber (noisy channel). After purification, the fidelity of polarization entanglement arises from 0.771 to 0.887 and the effective key rate in entanglement-based QKD increases from 0 to 0.332. The values of Clauser-Horne-Shimony-Holt (CHSH) inequality of polarization entanglement arises from 1.829 to 2.128. Moreover, by using one pair of hyperentanglement and deterministic controlled-NOT gate, the total purification efficiency can be estimated as 6.6x10^3 times than the experiment using two pairs of entangled states with spontaneous parametric down-conversion (SPDC) sources. Our results offer the potential to be implemented as part of a full quantum repeater and large scale quantum network., The typos in the title and abstract are modified

High Altitude Platform Station (HAPS) has the potential to provide global wireless connectivity and data services such as high-speed wireless backhaul, industrial Internet of things (IoT), and public safety for large areas not served by terrestrial networks. A unified HAPS design is desired to support various use cases and a wide range of requirements. In this paper, we present two architecture designs of the HAPS system: i) repeater based HAPS, and ii) base station based HAPS, which are both viable technical solutions. The energy efficiency is analyzed and compared between the two architectures using consumption factor theory. The system performance of these two architectures is evaluated through Monte Carlo simulations and is characterized in metrics of spectral efficiency using LTE band 1 for both single-cell and multi-cell cases. Both designs can provide good downlink spectral efficiency and coverage, while the uplink coverage is significantly limited by UE transmit power and antenna gain. Using directional antennas at the UEs can improve the system performance for both downlink and uplink.

Traditional light weight wireless communication modules like ZigBee, Bluetooth, LoRa have fixed frequency band and fixed protocol stack and hence lack flexibility of changing frequency, modulation techniques, waveforms etc. and may also prone to interference, jamming. Due to obstacles in between the transmitter and receiver, the communication coverage range is not large. But in emergency situations like war field or any disaster, there is need for robust communication in which the soldiers or public have to receive crucial information from base station. Software defined Radios like Universal Radio Software Peripheral (USRP), WARP boards needs to interface with computer for signal processing. Hence it is not suitable for drone based communication. So we proposed a solution to overcome bulkier system and limited communication range problem. In this work, a light-weight communication platform was developed which acts as a repeater for broadcasting voice commands that were transmitted from base station. The repeater is mounted on the drone and it is hovered at a certain altitude to make line of sight communication possible with both transmitter and receiver. This system was designed by interfacing Radio Frequency (RF) board present in USRP 2900 with Raspberry Pi 4, a credit card sized computer. The RF board overcomes the difficulty of standard wireless communication modules mentioned above, could easily mounted on drone, capable of communicating in different modulation schemes at multiple frequency bands and also one could implement cognitive radio features like spectrum sensing and taking automatic decisions based on data which is obtained from various sensors that are connected to Raspberry Pi.

Promising access to high-speed quantum networks relies on the creation of high-dimensional entangled memories that provide quantum communication with higher capacity of noisy quantum channels, thereby reducing the transmission time of information. Yet, the distribution of multidimensional entanglement between remote memory nodes is still faintly investigated. We propose an experimentally feasible protocol of deterministic generation of high-dimensional entanglement between distant multi-level atoms confined in high-finesse optical cavities and driven by laser pulses. Three-dimensional entanglement is generated deterministically between remote atoms by triggering a two-photon wavepacket, which mediates a superposition of states chosen by the laser pulse parameters. The efficient transfer of atomic states between remote nodes allows the construction of a three-dimensional quantum repeater, where the successful creation of entanglement can be verified by a simple method for reliable measurement of atomic ground Zeeman states., Comment: Accepted for publication at PRA. 10 pages, 5 figures

This paper presents a fault detection system for photovoltaic standalone applications based on Gaussian Process Regression (GPR). The installation is a communication repeater from the Confederación Hidrográfica del Ebro (CHE), public institution which manages the hydrographic system of Aragón, Spain. Therefore, fault-tolerance is a mandatory requirement, complex to fulfill since it depends on the meteorology, the state of the batteries and the power demand. To solve it, we propose an online voltage prediction solution where GPR is applied in a real and large dataset of two years to predict the behavior of the installation up to 48 hour. The dataset captures electrical and thermal measures of the lead-acid batteries which sustain the installation. In particular, the crucial aspect to avoid failures is to determine the voltage at the end of the night, so different GPR methods are studied. Firstly, the photovoltaic standalone installation is described, along with the dataset. Then, there is an overview of GPR, emphasizing in the key aspects to deal with real and large datasets. Besides, three online recursive multistep GPR model alternatives are tailored, justifying the selection of the hyperparameters: Regular GPR, Sparse GPR and Multiple Experts (ME) GPR. An exhaustive assessment is performed, validating the results with those obtained by Long Short-Term Memory (LSTM) and Nonlinear Autoregressive Exogenous Model (NARX) networks. A maximum error of 127 mV and 308 mV at the end of the night with Sparse and ME, respectively, corroborates GPR as a promising tool.

Indonesia as a country located on the equator often experiences disasters such as earthquakes, tsunamis, flash floods, etc. The resulting impact often cuts off the available communication infrastructure. The LAPAN-A2 satellite which has an equatorial orbit carries the payload voice repeater for amateur communications. This satellite circles the territory of Indonesia 14 times a day, therefore this payload is very useful as an alternative means of communication after a natural disaster. This paper describes the use of voice repeaters as an alternative means of communication by taking a regional study of the city of Palu.

Most of the mobile operators who are planning a transition from 4G to 5G will need to consider building a mobile network that is more standard-based and fully automated with a control on the complete network (software control). This will require the operators to plan their data center in a distributed manner, with a few data centers/sites marked as central data centers, where most of the network functions (NFs) and application functions will be deployed and several data centers marked as multi-access edge control (MEC) data centers. MEC data centers, where a few NFs like virtualized central units (vCUs), user plane functions (UPFs), local domain name systems (DNSs), and some local application functions will be deployed and many more smaller data centers where the virtualized distributed units (vDUs), and repeater interface units (RIUs) can reside are called far edge data centers.

The realization of a functional quantum repeater is one of the major research goals in long-distance quantum communication. Among the different approaches that are being followed, the one relying on quantum memories interfaced with deterministic quantum emitters is considered as one of the most promising solutions. In this work, we focus on the hardware to implement memory-based quantum-repeater schemes that rely on semiconductor quantum dots (QDs) for the generation of polarization entangled photons. Going through the most relevant figures of merit related to efficiency of the photon source, we select significant developments in fabrication, processing and tuning techniques aimed at combining high degree of entanglement with on-demand pair generation, with a special focus on the progress achieved in the representative case of the GaAs system. We proceed to offer a perspective on integration with quantum memories, both highlighting preliminary works on natural–artificial atomic interfaces and commenting a wide choice of currently available and potentially viable memory solutions in terms of wavelength, bandwidth and noise-requirements. To complete the overview, we also present recent implementations of entanglement-based quantum communication protocols with QDs and highlight the next challenges ahead for the implementation of practical quantum networks.

The soft gamma-ray repeater candidate SGR 0755$-$2933 was discovered in 2016 by Swift/BAT, which detected a short ($\sim$30 ms) powerful burst typical of magnetars. To understand the nature of the source, we present here an analysis of follow-up observations of the tentative soft X-ray counterpart of the source obtained with Swift/XRT, NuSTAR and Chandra. From our analysis we conclude that, based on the observed counterpart position and properties, it is actually not a soft gamma ray repeater but rather a new high mass X-ray binary. We suggest to refer to it as 2SXPS J075542.5$-$293353. We conclude, therefore, that the available data do not allow us to confirm existence and identify the true soft X-ray counterpart to the burst event. Presence of a soft counterpart is, however, essential to unambiguously associate the burst with a magnetar flare, and thus we conclude that magnetar origin of the burst and precise burst location remain uncertain and require further investigation., Comment: 6 pages, 6 figures, accepted in A&A

In a quantum network that successfully creates links, shared Bell states between neighboring repeater nodes, with probability $p$ in each time slot, and performs Bell State Measurements at nodes with success probability $q, Comment: 13 pages, q0 figures, Accepted in IEEE QCE 2021

The rate at which quantum communication tasks can be performed using direct transmission is fundamentally hindered by the channel loss. Quantum repeaters allow, in principle, to overcome these limitations, but their introduction necessarily adds an additional layer of complexity to the distribution of entanglement. This additional complexity - along with the stochastic nature of processes such as entanglement generation, Bell swaps, and entanglement distillation - makes finding good quantum repeater schemes non-trivial. We develop an algorithm that can efficiently perform a heuristic optimisation over a subset of quantum repeater schemes for general repeater platforms. We find a strong improvement in the generation rate in comparison to an optimisation over a simpler class of repeater schemes based on BDCZ repeater schemes. We use the algorithm to study three different experimental quantum repeater implementations on their ability to distribute entanglement, which we dub \emph{information processing} implementations, \emph{multiplexed} implementations, and combinations of the two. We perform this heuristic optimisation of repeater schemes for each of these implementations for a wide range of parameters and different experimental settings. This allows us to make estimates on what are the most critical parameters to improve for entanglement generation, how many repeaters to use, and which implementations perform best in their ability to generate entanglement., 39 pages, 29 figures

The scaling in the CMOS technology has derived a new route to the miniaturization of semiconductor devices. As technology is changing day by day, more and more transistors are integrated into a single chip. As the transistor increases in number, the operating speed should also increase. Power consumption of the circuit increases with the increase in the count of transistors on the die. The paper addresses the effect of MTCMOS in reducing power consumption. MTCMOS technique is a power or gating structure used to reduce leakage current in the standby state and also reduced static power consumption. Experimental results show that 60–19% leakage power reduction compared to the CMOS technique. The investigation is further continued in reducing crosstalk noise. In this paper, the crosstalk noise which occurs in between two wire interconnects due to coupling capacitance is reduced by using MTCMOS repeaters. The simulation is carried in the Cadence tool at 180 nm technology. MTCMOS repeater uses low power 41.323 pW compared to CMOS repeater of 17.872 nW.

The origins of fast radio bursts (FRBs), astronomical transients with millisecond timescales, remain unknown. One of the difficulties stems from the possibility that observed FRBs could be heterogeneous in origin; as some of them have been observed to repeat, and others have not. Due to limited observing periods and telescope sensitivities, some bursts may be misclassified as non-repeaters. Therefore, it is important to clearly distinguish FRBs into repeaters and non-repeaters, to better understand their origins. In this work, we classify repeaters and non-repeaters using unsupervised machine learning, without relying on expensive monitoring observations. We present a repeating FRB recognition method based on the Uniform Manifold Approximation and Projection (UMAP). The main goals of this work are to: (i) show that the unsupervised UMAP can classify repeating FRB population without any prior knowledge about their repetition, (ii) evaluate the assumption that non-repeating FRBs are contaminated by repeating FRBs, and (iii) recognise the FRB repeater candidates without monitoring observations and release a corresponding catalogue. We apply our method to the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) database. We found that the unsupervised UMAP classification provides a repeating FRB completeness of 95 per cent and identifies 188 FRB repeater source candidates from 474 non-repeater sources. This work paves the way to a new classification of repeaters and non-repeaters based on a single epoch observation of FRBs., Comment: 10 pages, 9 figures, accepted for publication in MNRAS. For summary video, please see https://youtu.be/fWfvfFPDhcQ

Quantum repeaters are indispensable tools for long-distance quantum communication. However, frequency matching between entangled photon sources and remote quantum memories (QMs) is difficult, which is an obstacle to the implementation of quantum repeaters. In this paper, we demonstrate a method to achieve the coupling of a Pr:YSO as a fixed-time QM with a single telecommunication-wavelength photon through frequency stabilization using an optical frequency comb over all applied laser wavelengths. The demonstrated method can lead to the implementation of a quantum repeater scheme enabling an improvement of the entanglement generation rate, paving the way for long-distance quantum communication., Comment: 16 pages, 6 figures

This paper determines the location of Radio Relay UAVs by considering three situations. We find the latitude and longitude distance can be used for all points are "discrete points". If all points are "basic pieces", this paper uses a geometric drawing board to illustrate the "gridded processing" process, and determine the location of the high generation repeater by calculating points, mark points and grid. For both "discrete" points and "basic pieces" points, they are operated as (1) and (2) respectively base on classifing them. All primary repeaters and discrete points not connected to any relay station are obtained. Finally, iterates repeatedly until the geographical distribution of all relay stations.

The Australian wildfires in 2019–2020 have brought suffering to the Australian people. It is essential to use models to help the Victorian government monitor and predict the occurrence and development of fires to the greatest extent possible under the principles of safety and economy to facilitate rapid response. Through the idea of K -means algorithm and greedy algorithm, we, respectively, analyzed cities and rural areas at different altitudes and combined the altitude with the obtained clusters; the analysis from the established model shows that, for cities, cluster areas with smaller clusters with an altitude of less than 1600 meters and areas with smaller clusters with an altitude of greater than or equal to 1800 meters are covered by an EOC; for areas with larger clusters less than or equal to 600 meters above the sea level and areas with larger clusters greater than or equal to 1000 meters above the sea level, we use two EOCs for coverage; for rural areas, all areas with smaller clusters are covered by one EOC, while for areas with larger clusters where the altitude is less than or equal to 1000 meters and the altitude is greater than or equal to 1600 meters, we use two EOCs for coverage; also, obtained through greedy algorithm analysis, one EOC corresponds to 14 SSA UAVs and 8 repeater UAVs, and two EOCs correspond to 12 repeater UAVs and 26 SSA UAVs. We have a reason to believe that, through our mathematical model and the leaps in drone technology, it will have a long-term and profound impact on Australia’s wildfire control.

Interrupted-sampling repeater jamming (ISRJ) is a new type of DRFM-based jamming designed for linear frequency modulation (LFM) signals. By intercepting the radar signal slice and retransmitting it many times, ISRJ can obtain radar coherent processing gain so that multiple false target groups can be formed after pulse compression (PC). According to the distribution characteristic of the echo signal and the coherence of ISRJ to radar signal, a new method for ISRJ suppression is proposed in this study. In this method, the position of the real target is determined using a gated recurrent unit neural network (GRU-Net), and the real target can be, therefore, reconstructed by adaptive filtering in the sparse representation of the echo signal based on the target locating result. The reconstruction result contains only the real target, and the false target groups formed by ISRJ are suppressed completely. The target locating accuracy of the proposed GRU-Net can reach 92.75%. Simulations have proved the effectiveness of the proposed method.

We used a new spectral-fitting technique to identify a subpopulation of 6 narrow-band giant pulses from the Crab pulsar out of a total of 1578. These giant pulses were detected in 77 minutes of observations with the 46-m dish at the Algonquin Radio Observatory at 400-800 MHz. The narrow-band giant pulses consist of both main- and inter-pulses, thereby being more likely to be caused by an intrinsic emission mechanism as opposed to a propagation effect. Fast Radio Bursts (FRBs) have demonstrated similar narrow-band features while only little has been observed in the giant pulses of pulsars. We report the narrow-band giant pulses with $\Delta \nu / \nu$ on the order of 0.1, which is close to the value of 0.05 reported for the repeater FRB 20190711A. Hence, the connection between FRBs and giant pulses of pulsars is further established., Comment: 7 pages, 3 figures

We examine and verify the mid-infrared transitions of 77Se+ deep donors in Silicon. We aim to use implanted Se ions as nuclear-spin/photon interfaces for on-chip quantum repeater structures.

The basic principle of quantum mechanics guarantee the unconditional security of quantum key distribution (QKD) at the cost of inability of amplification of quantum state. As a result, despite remarkable progress in worldwide metropolitan QKD networks over the past decades, long haul fiber QKD network without trustful relay has not been achieved yet. Here, through sending-or-not-sending (SNS) protocol, we complete a twin field QKD (TF-QKD) and distribute secure keys without any trusted repeater over a 511 km long haul fiber trunk linking two distant metropolitans. Our secure key rate is around 3 orders of magnitudes greater than what is expected if the previous QKD field test system over the same length were applied. The efficient quantum-state transmission and stable single-photon interference over such a long distance deployed fiber paves the way to large-scale fiber quantum networks., Comment: 32 pages, 8 figures

Quantum communication enables the implementation of tasks that are unachievable with classical resources. However, losses on the communication channel preclude the direct long-distance transmission of quantum information in many relevant scenarios. In principle, quantum repeaters allow one to overcome losses. However, realistic hardware parameters make long-distance quantum communication a challenge in practice. For instance, in many protocols an entangled pair is generated that needs to wait in quantum memory until the generation of an additional pair. During this waiting time the first pair decoheres, impacting the quality of the final entanglement produced. At the cost of a lower rate, this effect can be mitigated by imposing a cutoff condition. For instance, a maximum storage time for entanglement after which it is discarded. In this article, we optimize the cutoffs for quantum repeater chains. First, we develop an algorithm for computing the probability distribution of the waiting time and fidelity of entanglement produced by repeater chain protocols which include a cutoff. Then, we use the algorithm to optimize cutoffs in order to maximize the secret-key rate between the end nodes of the repeater chain. In this article, we find that the use of the optimal cutoff extends the parameter regime for which secret key can be generated and, moreover, significantly increases the secret-key rate for a large range of parameters.