Quantum communications promise to revolutionize the way information is exchanged and protected. Unlike their classical counterpart, they are based on dim optical pulses that cannot be amplified by ...conventional optical repeaters. Consequently, they are heavily impaired by propagation channel losses, confining their transmission rate and range below a theoretical limit known as repeaterless secret key capacity. Overcoming this limit with today’s technology was believed to be impossible until the recent proposal of a scheme that uses phase-coherent optical signals and an auxiliary measuring station to distribute quantum information. Here, we experimentally demonstrate such a scheme for the first time and over significant channel losses, in excess of 90 dB. In the high loss regime, the resulting secure key rate exceeds the repeaterless secret key capacity, a result never achieved before. This represents a major step in promoting quantum communications as a dependable resource in today’s world.A proof-of-principle experiment on twin-field quantum key distribution is demonstrated. The key rate overcomes the repeaterless secret key capacity bound limit at channel losses of 85 dB, corresponding to 530 km of ultralow-loss optical fibre.
The development of quantum networks will be paramount towards practical and secure telecommunications. These networks will need to sign and distribute information between many parties with ...information-theoretic security, requiring both quantum digital signatures (QDS) and quantum key distribution (QKD). Here, we introduce and experimentally realise a quantum network architecture, where the nodes are fully connected using a minimum amount of physical links. The central node of the network can act either as a totally untrusted relay, connecting the end users via the recently introduced measurement-device-independent (MDI)-QKD, or as a trusted recipient directly communicating with the end users via QKD. Using this network, we perform a proof-of-principle demonstration of QDS mediated by MDI-QKD. For that, we devised an efficient protocol to distil multiple signatures from the same block of data, thus reducing the statistical fluctuations in the sample and greatly enhancing the final QDS rate in the finite-size scenario.
The time-reversal technique has been successfully used in structural health monitoring (SHM) for quantitative imaging of damage. However, the technique is very time-consuming when it is implemented ...in the time domain. In this paper, we study the technique in the frequency-wavenumber (f-k) domain for fast real-time imaging of multiple damage sites in plates using scattered flexural plate waves. Based on Mindlin plate theory, the time reversibility of dispersive flexural waves in an isotropic plate is theoretically investigated in the f-k domain. A fast damage imaging technique is developed by using the cross-correlation between the back-propagated scattered wavefield and the incident wavefield in the frequency domain. Numerical simulations demonstrate that the proposed technique cannot only localize multiple damage sites but also potentially identify their sizes. Moreover, the time-reversal technique in the f-k domain is about two orders of magnitude faster than the method in the time domain. Finally, experimental testing of an on-line SHM system with a sparse piezoelectric sensor array is conducted for fast multiple damage identification using the proposed technique.
The art of imparting information onto a light wave by optical signal modulation is fundamental to all forms of optical communication. Among many schemes, direct modulation of laser diodes stands out ...as a simple, robust, and cost-effective method. However, the simultaneous changes in intensity, frequency, and phase have prevented its application in the field of secure quantum communication. Here, we propose and experimentally demonstrate a directly phase-modulated light source which overcomes the main disadvantages associated with direct modulation and is suitable for diverse applications such as coherent communications and quantum cryptography. The source separates the tasks of phase preparation and pulse generation between a pair of semiconductor lasers leading to very pure phase states. Moreover, the cavity-enhanced electro-optic effect enables the first example of subvolt half-wave phase modulation at high signal rates. The source is compact, stable, and versatile, and we show its potential to become the standard transmitter for future quantum communication networks based on attenuated laser pulses.
HUBS: Hot Universe Baryon Surveyor Cui, W.; Chen, L.-B.; Gao, B. ...
Journal of low temperature physics,
04/2020, Letnik:
199, Številka:
1-2
Journal Article
Recenzirano
Hot Universe Baryon Surveyor (HUBS) is proposed in China as a major X-ray mission for the next decade. It is designed to be highly focused scientifically, with two primary objectives: (1) detecting ...X-ray emission from hot baryons in intergalactic medium and circumgalactic medium (CGM), and characterizing their physical and chemical properties; (2) studying, based on the observations, the accretion and feedback processes that are thought to be highly relevant to the heating and chemical enrichment of the baryons in the CGM. Because of very low densities, the signal is expected to be very weak and thus technically difficult to detect. On the other hand, the spectrum of the emission is expected to be line rich, so it would be effective for detecting the hot baryons in bright emission lines. For that, an instrument with high spectral resolution, large effective area and large field of view (FoV) would be required. HUBS will couple a TES-based X-ray imaging spectrometer to a large FoV X-ray telescope to satisfy these requirements. A preliminary design of HUBS is presented.
As coal mining operations progress to depths exceeding 1000 m, the long-term large-scale deformation of deep roadways has been a subject of serious concern in regions with high in situ stress fields. ...The instability of these roadways affects the safety and efficiency of deep coal mines. To solve this support problem, a new type of strengthening support structure, the concrete-filled steel tubular support (CSTS), was developed. This support is composed of a seamless steel tube bent to conform to the cross-section of the roadway and filled with concrete. According to both mechanical and structural performance testing, the ultimate bearing capacity of the tested CSTS is between 1664 kN and 2235 kN, values 3–5 times that of a U-type steel support. In addition, the circular cross-section of the steel tube has a higher structural stability than the U-shaped cross-section and is not prone to torsional deformation. Because of the clear advantages of both the high bearing capacity and structural stability, a support system combining both CSTS and a bolt-cable system can effectively control the long-term large-scale deformation of a deep roadway. Following a field application within a 1200-m-deep roadway in the Huafeng coal mine in China, the large-scale deformation of the roadway, which previously exceeded 1000 mm, was reduced to less than 30 mm. Furthermore, this roadway no longer required frequent repair after the application of the CSTS. To date, the CSTS has been successfully applied and providing effective support in over 20 deep mines in China.
Producing quantum states at random has become increasingly important in modern quantum science, with applications being both theoretical and practical. In particular, ensembles of such randomly ...distributed, but pure, quantum states underlie our understanding of complexity in quantum circuits
and black holes
, and have been used for benchmarking quantum devices
in tests of quantum advantage
. However, creating random ensembles has necessitated a high degree of spatio-temporal control
placing such studies out of reach for a wide class of quantum systems. Here we solve this problem by predicting and experimentally observing the emergence of random state ensembles naturally under time-independent Hamiltonian dynamics, which we use to implement an efficient, widely applicable benchmarking protocol. The observed random ensembles emerge from projective measurements and are intimately linked to universal correlations built up between subsystems of a larger quantum system, offering new insights into quantum thermalization
. Predicated on this discovery, we develop a fidelity estimation scheme, which we demonstrate for a Rydberg quantum simulator with up to 25 atoms using fewer than 10
experimental samples. This method has broad applicability, as we demonstrate for Hamiltonian parameter estimation, target-state generation benchmarking, and comparison of analogue and digital quantum devices. Our work has implications for understanding randomness in quantum dynamics
and enables applications of this concept in a much wider context
.
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