Security loopholes exploiting the flaws of practical apparatus, especially non-ideal photon detectors, are pressing issues in practical quantum communication. We propose a simple quantum secure ...direct communication protocol based on single-photon Bell-state measurement and remove side-channel attacks on photon detectors. This quantum communication protocol in principle works in a deterministic way, and it does not require the two-photon interference of photons from independent sources. The single-photon Bell-state measurement with a unity efficiency can be constructed with only linear optics, which significantly simplifies its experimental implementation. Furthermore, we prove that our quantum secure direct communication protocol is immune to general detector-side-channel attacks.
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Quantum secure direct communication (QSDC) attracts much attention for it can transmit secret messages directly without sharing a key. In this article, we propose a one-step QSDC ...protocol, which only requires to distribute polarization-spatial-mode hyperentanglement for one round. In this QSDC protocol, the eavesdropper cannot obtain any message, so that this protocol is unconditionally secure in principle. This protocol is a two-way quantum communication and has high capacity for it can transmit two bits of secret messages with one pair of hyperentanglement. With entanglement fidelities of both polarization and spatial-mode degrees of freedom being 0.98, the maximal communication distance of this one-step QSDC can reach about 216 km. QSDC can also be used to generate the key. In this regard, the key generation rate is estimated about 2.5 times of that in the entanglement-based QKD with the communication distance of 150 km. With the help of future quantum repeaters, this QSDC protocol can provide unconditionally secure communication over arbitrarily long distance.
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“Device-independent” not only represents a relaxation of the security assumptions about the internal working of the quantum devices, but also can enhance the security of the quantum ...communication. In the paper, we put forward the first device-independent quantum secure direct communication (DI-QSDC) protocol and analyze its security and communication efficiency against collective attacks. Under practical noisy quantum channel condition, the photon transmission loss and photon state decoherence would reduce DI-QSDC’s communication quality and threaten its absolute security. For solving the photon transmission loss and decoherence problems, we adopt noiseless linear amplification (NLA) protocol and entanglement purification protocol (EPP) to modify the DI-QSDC protocol. With the help of the NLA and EPP, we can guarantee DI-QSDC’s absolute security and effectively improve its communication quality.
By preparing a sensor system around isolated exceptional points, one can obtain a great enhancement of the sensitivity benefiting from the non‐Hermiticity. However, this comes at the cost of ...reduction of the flexibility of the system, which is critical for practical applications. By generalizing the exceptional points to exceptional surfaces, it has been theoretically proposed recently that enhanced sensitivity and flexibility can be combined. Here, an exceptional surface is experimentally demonstrated in a non‐Hermitian photonic sensing system, which is composed of a whispering‐gallery‐mode microresonator and two nanofiber waveguides, resulting in a unidirectional coupling between two degenerate counter‐propagating modes with an external optical isolator. The system is simple, robust, and can be easily operated around an exceptional surface. On the one hand, sensitivity enhancement is observed by monitoring the resonant frequency splitting caused by small perturbations. This demonstration of exceptional‐surface‐enhanced sensitivity paves the way for practical non‐Hermitian sensing applications. On the other hand, the suppression of frequency splitting around the exceptional surface is also shown for the first time.
Exceptional surfaces are experimentally realized in the higher‐dimensional synthetic space. The unidirectional coupling between two degenerate modes can be achieved benefitting from an ingenious design within a single whispering‐gallery‐mode microresonator. The sensor operating at an exceptional surface can combine enhanced sensitivity with flexible experimental conditions.
In recent years, researchers have proposed many graph-based multi-view clustering (GMC) algorithms to solve the multi-view clustering (MVC) problem. However, there are still some limitations in the ...existing GMC algorithm. In these algorithms, a graph is usually constructed to represent the relationship between the samples in a view; however, it cannot represent the relationship very well since it is often preconstructed. In addition, these algorithms ignore the robustness problem of each graph and high-level information between different graphs. Then, in the paper, we propose a novel MVC method, i.e., robust and optimal neighborhood graph learning for MVC (RONGL/MVC). Specifically, we first build an initial graph for each view. However, these initial graphs cannot represent the relationship between the samples in each view well, so we look for the optimal graph with k connected components in the neighborhood of each initial graph, where k is the number of clusters. Then, to improve the robustness of RONGL/MVC, we reconstruct the optimal graph with the self-representation matrix. Furthermore, we stack all the self-representation matrices into a tensor and impose the tensor low-rank constraint, which can maximize consistent features and explore the high-order relationship between optimal graphs. In addition, we provide an optimization strategy by utilizing the Augmented Lagrange Multiplier (ALM) method. Experimental results on several datasets indicate that RONGL/MVC outperforms state-of-the-art methods.
High-sensitivity gyroscope is widely used for rotation detection in several practical applications. Recently, exceptional points (EPs) have garnered considerable attention for enhancing the ...sensitivity of sensors based on optical cavities. Here, we propose an EP-enhanced optical gyroscope based on mechanical parity-time (PT) symmetry in a microcavity system. We demonstrate that by pumping the two optical modes with different colors, i.e., blue and red detuning, an effective mechanical PT-symmetric system can be obtained, and the system can be prepared at EP with appropriate parameters. The sensitivity of gyroscope at EP was enhanced by more than one order of magnitude in the weak perturbation regime as compared to that at diabolic point. This indicates that the sensitivity of gyroscope can be effectively enhanced by monitoring the mechanical modes rather than the optical modes. Overall, our work provides a promising approach to design high-sensitivity gyroscopes in optical microcavities and is potentially useful in a variety of research fields including fundamental physics and precision measurement.
Recently, with the assumption that samples can be reconstructed by themselves, subspace clustering (SC) methods have achieved great success. Generally, SC methods contain some parameters to be tuned, ...and different affinity matrices can obtain with different parameter values. In this paper, for the first time, we study a method for fusing these different affinity matrices to promote clustering performance and provide the corresponding solution from a multi-view clustering (MVC) perspective. That is, we argue that the different affinity matrices are consistent and complementary, which is similar to the fundamental assumption of MVC methods. Based on this observation, in this paper, we use least squares regression (LSR), which is a typical SC method, as an example since it can be efficiently optimized and has shown good clustering performance and we propose a novel robust least squares regression method from an MVC perspective (RLSR/MVCP). Specifically, we first utilize LSR with different parameter values to obtain different affinity matrices. Then, to fully explore the information contained in these different affinity matrices and to remove noise, we further fuse these affinity matrices into a tensor, which is constrained by the tensor low-rank constraint, i.e., the tensor nuclear norm (TNN). The two steps are combined into a framework that is solved by the augmented Lagrange multiplier (ALM) method. The experimental results on several datasets indicate that RLSR/MVCP has very encouraging clustering performance and is superior to state-of-the-art SC methods.
Subaerial continental crust plays a fundamental role in modulating the composition of the ocean, atmosphere, and biosphere, but the timing and rate of continental emergence above sea level remain ...unclear. Here, we use the zircon oxygen isotopic compositions of early Paleoproterozoic metasediment‐derived granitoids from the southwestern Yangtze Block to constrain the rapidity of continental emergence. Statistical analyses of compiled igneous and detrital zircon oxygen isotopic database show a rapid increase in zircon δ18O at ∼2.36 Ga. We suggest that this isotopic shift is best explained by a significant increase of continental freeboard between ∼2.43 and ∼2.36 Ga due to the increasing strength of the continental lithosphere since the late Archean, concomitantly yielding a high‐δ18O sedimentary reservoir. Subsequent melting of these high‐δ18O sediments in a variety of tectonic regimes results in high zircon δ18O.
Plain Language Summary
The timing and pattern of continental emergence are highly debated due to the lack of associated geological records back into Earth deep time, particularly for the early Paleoproterozoic era, when the earth likely experienced a “tectono‐magmatic lull” period. In this study, the early Paleoproterozoic high δ18O (>7.5‰) metasediment‐derived granitoids are identified in the SW Yangtze Block. Statistical analyses were carried out on the globally compiled igneous and detrital zircon δ18O database, detecting that a rapid increase in zircon δ18O at ∼2.36 Ga. We propose a geodynamic driver for the formation of a high‐δ18O sedimentary reservoir during the early Paleoproterozoic due to significant continental emergence at that time could geodynamically account for this isotopic shift.
Key Points
Early Paleoproterozoic high δ18O metasediment‐derived granites were identified in the SW Yangtze
The rapid increase in zircon δ18O at ∼2.36 Ga was related to a high‐δ18O sedimentary reservoir
Continental crust was significantly emerged above sea level since the early Paleoproterozoic
Rapid development of supercomputers and the prospect of quantum computers are posing increasingly serious threats to the security of communication. Using the principles of quantum mechanics, quantum ...communication offers provable security of communication and is a promising solution to counter such threats. Quantum secure direct communication (QSDC) is one important branch of quantum communication. In contrast to other branches of quantum communication, it transmits secret information directly. Recently, remarkable progress has been made in proof-of-principle experimental demonstrations of QSDC. However, it remains a technical feat to bring QSDC into a practical application. Here, we report the implementation of a practical quantum secure communication system. The security is analyzed in the Wyner wiretap channel theory. The system uses a coding scheme of concatenation of low-density parity-check (LDPC) codes and works in a regime with a realistic environment of high noise and high loss. The present system operates with a repetition rate of 1 MHz at a distance of 1.5 kilometers. The secure communication rate is 50 bps, sufficient to effectively send text messages and reasonably sized files of images and sounds.
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