Abstract
We seek to design experimentally feasible broadband, temporally multiplexed optical quantum memory with near-term applications to telecom bands. Specifically, we devise dispersion ...compensation (DC) for an impedance-matched narrow-band quantum memory by exploiting Raman processes over two three-level atomic subensembles, one for memory and the other for DC. DC provides impedance matching over more than a full cavity linewidth. Combined with 1 s spin-coherence lifetime the memory could be capable of power efficiency exceeding 90% leading to 10
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modes for temporal multiplexing. Our design could lead to significant multiplexing enhancement for quantum repeaters to be used for telecom quantum networks.
Quantum communication is a secure way to transfer quantum information and to communicate with legitimate parties over distant places in a network. Although communication over a long distance has ...already been attained, technical problem arises due to unavoidable loss of information through the transmission channel. Quantum repeaters can extend the distance scale using entanglement swapping and purification scheme. Here we demonstrate the working of a quantum repeater by the above two processes. We use IBM’s real quantum processor ‘ibmqx4’ to create two pair of entangled qubits and design an equivalent quantum circuit which consequently swaps the entanglement between the two pairs. We then develop a novel purification protocol which enhances the degree of entanglement in a noisy channel that includes combined errors of bit-flip, phase-flip and phase-change error. We perform quantum state tomography to verify the entanglement swapping between the two pairs of qubits and working of the purification protocol.
The theory and experiment of quantum information have been studied extensively in recent years, and the feasibility of quantum communication has been proved. Although the fundamental technology is ...not yet mature, research on quantum internet should be conducted. To implement quantum internet, an architecture that describes how quantum nodes are linked to form networks and how protocol functions are vertically composed need to be developed urgently. In this paper, we present a novel design of a cluster-based structure to describe how quantum nodes are interconnected, and how the structure can improve the performance of qubit transmission and reduce the network complexity. The idea of the quantum local area network (QLAN) is proposed as an essential component of the quantum internet. Besides, each quantum repeater links to neighboring repeaters to form a core network, and multiple QLANs are connected through the core network. The core network can be grouped into different hierarchical quantum repeater networks according to needed service requirements. For the sake of interoperability and fast prototyping, we adopt the idea of OSI layering model of the current Internet in the design of quantum internet. Finally, we elaborate on the composition of quantum nodes and the realization of end-to-end communication.
Steady technological advances and recent milestones such as intercontinental quantum communication and the first implementation of medium-scale quantum networks are paving the way for the ...establishment of the quantum internet, a network of nodes interconnected by quantum channels. Here we build upon recent models for quantum networks based on optical fibers by considering the effect of a non-uniform distribution of nodes, more specifically based on the demographic data of the federal states in Brazil. We not only compute the statistical properties of this more realistic network, comparing its features with previous models but also employ it to compute the repetition rates for entanglement swapping, an essential protocol for quantum communication based on quantum repeaters.
•Developed a quantum network model using optical fibers, incorporating the impact of a non-uniform node distribution.•Analyzed the statistical properties of such quantum network, leveraging demographic and geographical data from Brazil.•Applied the developed model to compute repetition rates for entanglement swapping.
Recently, interrupted sampling repeater jamming (ISRJ) based on digital radio frequency memory (DRFM), which could easily form high-power false targets, has severely impacted radar detection ...capabilities. Conventional anti-ISRJ techniques ignore the operating characteristics of the jammer. Once the anti-ISRJ algorithm and the features of the jammer are mismatched, undesirable jamming residues or signal loss appear. In order to avoid these unwanted performance losses, an algorithm jointing the jam perception and the adaptive waveform is developed in this paper. First, a bi-directional Constant False Alarm Rate (CFAR) detector is introduced to locate and estimate the jamming component in radar echo. An ISRJ feature vector is then built to reconstruct and cancel jamming components for accurate detection under ISRJ. Second, an adaptive anti-ISRJ waveform is developed based on the vector, leading the DRFM to retransmit signals orthogonal to the real detection signal. Besides, the particle swarm optimization (PSO) algorithm efficiently works out the optimal waveform parameters to improve the suppression performance. As radar switches to the adaptive anti-ISRJ waveform, long-term suppression of ISRJ is achieved without locating, estimating, and suppressing the ISRJ components in each echo. Simulated experiments demonstrate that the suggested algorithm can accurately detect radar targets under ISRJ.
Despite the successful launch of Advanced Television Systems Committee (ATSC) 3.0 broadcasting worldwide, broadcasters are facing obstacles in constructing void‐less large‐scale single‐frequency ...networks (SFNs). The bottleneck is the absence of decent on‐channel repeater (OCR) solutions necessary for SFNs. In the real world, OCRs suffer from the maleficent feedback interference (FI) problem, which overwhelms the desired input signal. Moreover, the undesired multipaths between studio‐linked transmitters and the OCR deteriorate the forward signals' quality as well. These problems crucially restrict the feasibility of conventional OCR systems, arousing the strong need for cost‐worthy advanced OCR solutions. This paper presents an ATSC 3.0‐specific solution of advanced OCR that solves the FI problem and refines the input signal. To this end, the FI canceler and channel equalizer functionalities are carefully implemented into the OCR system. The presented OCR system is designed to be fully compliant with the ATSC 3.0 specifications and performs a fast and efficient signal processing by exploiting the specific frame structure. The real product of ATSC 3.0 OCR is fabricated as well, and its feasibility is verified via field and laboratory experiments. The implemented solution is installed at a commercial on‐air site and shown to provide substantial coverage gain in practice.
Reflectarray surfaces (RASs) can be useful as passive repeaters or intelligent reflecting surfaces (IRSs) in communication networks by providing nonspecular reflection of an incident wave. To provide ...adequate signal at a given location, the radar cross section (RCS), and therefore physical size, of the RAS needs to be maximized. This inevitably reduces the beamwidth and bandwidth of the RCS pattern, severely limiting their practical implementation. This article considers a shaped reflector profiled as a truncated ellipse that can give a widened "equi-ripple" beam that addresses these problems. It is shown that by careful selection of the phase profile, the beamwidth can be expanded by a factor of 3.5 (or even 7.5 if lower roll-off in the RCS pattern is allowed) with a corresponding increase in the useable bandwidth. The tradeoff is a reduction in the peak RCS. By increasing the physical size of the reflector, this loss of RCS can be compensated for, still resulting in at least 1.8 times the beamwidth of a flat reflector. The shaped reflector can be realized as an RAS using a closed-form expression. A typical design at 28 GHz is considered. In principle a 22 <inline-formula> <tex-math notation="LaTeX">\times22 </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">0.4\lambda </tex-math></inline-formula> spaced array offers illumination from 40° to 50° over 26-32 GHz, considerably better than the unshaped beam.
This paper proposes a long-distance multi-load wireless power transfer (WPT) system with a constant voltage (CV) output for each load. A repeater unit consisting of two bipolar repeater coils is ...designed to power the load. Multiple repeater units are placed in a line and the power can be transferred from one unit to the next. Each repeater unit corresponds to one load and multiple loads can be powered simultaneously. The two repeater coils in the same repeater unit are placed perpendicularly to eliminate the magnetic coupling between them. In each repeater unit, a compensation capacitor is placed in series with the transmitting coil while two extra compensation capacitors form a series-parallel (SP) structure for the receiving coil. When neglecting the coil's parasitic resistance, the CV characteristics can be obtained, which enables the independent and flexible power control of each load. Moreover, the influence of the parasitic resistances on the system performance is analysed. Such a system is especially suitable for powering the gate drivers in a high-voltage converter where multiple insulated gate bipolar transistors (IGBTs) are connected in series. An experimental setup with six loads is constructed to validate the proposed system. The maximum system efficiency can reach 88.1%.
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Entanglement purification is to distill high-quality entangled states from low-quality entangled states. It is a key step in quantum repeaters, determines the efficiency and ...communication rates of quantum communication protocols, and is hence of central importance in long-distance communications and quantum networks. In this work, we report the first experimental demonstration of deterministic entanglement purification using polarization and spatial mode hyperentanglement. After purification, the fidelity of polarization entanglement arises from 0.268±0.002 to 0.989±0.001. Assisted with robust spatial mode entanglement, the total purification efficiency can be estimated as 109 times that of the entanglement purification protocols using two copies of entangled states when one uses the spontaneous parametric down-conversion sources. Our work may have the potential to be implemented as a part of full repeater protocols.
The interrupted sampling repeater jamming (ISRJ) produces multiple false targets after pulse compression, making it difficult for radar to detect real targets. In this paper, an anti-ISRJ algorithm ...is developed based on the joint design of the waveform and mismatched filter with expanded mainlobe. First, to prevent false alarms when the range sidelobes and jamming peaks of the filter output are too high, the sum of the peak sidelobe level of the waveform compressed with mismatched filter and the peak level of the ISRJ signal compressed with mismatched filter is taken as an optimization criterion for minimization. Meanwhile, a penalty function is used to control the mainlobe shape of the correlation function between the mainlobe. To maximize the transmitted power efficiency of the radar and control the signal-to-noise ratio loss caused by the mismatched filter, a constant modular constraint for the waveform and an energy constraint for the filter are adopted. Then, an iterative algorithm based on the majorization- minimization framework is proposed to solve the joint design problem. In each iteration, an analytical expression is derived to realize the simultaneous updating of the waveform and filter. The convergence of the proposed algorithm is proven, and its computational complexity is analyzed. Finally, simulations are provided to demonstrate the effectiveness of the proposed algorithm. Compared with existing algorithms, the waveform and filter designed in this paper exhibit better pulse compression performance and anti-jamming ability.
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