We report the first experimental demonstration of quantum entanglement among ten spatially separated single photons. A near-optimal entangled photon-pair source was developed with simultaneously a ...source brightness of ∼12 MHz/W, a collection efficiency of ∼70%, and an indistinguishability of ∼91% between independent photons, which was used for a step-by-step engineering of multiphoton entanglement. Under a pump power of 0.57 W, the ten-photon count rate was increased by about 2 orders of magnitude compared to previous experiments, while maintaining a state fidelity sufficiently high for proving the genuine ten-particle entanglement. Our work created a state-of-the-art platform for multiphoton experiments, and enabled technologies for challenging optical quantum information tasks, such as the realization of Shor's error correction code and high-efficiency scattershot boson sampling.
Creating large-scale entanglement lies at the heart of many quantum information processing protocols and the investigation of fundamental physics. For multipartite quantum systems, it is crucial to ...identify not only the presence of entanglement but also its detailed structure. This is because in a generic experimental situation with sufficiently many subsystems involved, the production of so-called genuine multipartite entanglement remains a formidable challenge. Consequently, focusing exclusively on the identification of this strongest type of entanglement may result in an all or nothing situation where some inherently quantum aspects of the resource are overlooked. On the contrary, even if the system is not genuinely multipartite entangled, there may still be many-body entanglement present in the system. An identification of the entanglement structure may thus provide us with a hint about where imperfections in the setup may occur, as well as where we can identify groups of subsystems that can still exhibit strong quantum-information-processing capabilities. However, there is no known efficient methods to identify the underlying entanglement structure. Here, we propose two complementary families of witnesses for the identification of such structures. They are based, respectively, on the detection of entanglement intactness and entanglement depth, each applicable to an arbitrary number of subsystems and whose evaluation requires only the implementation of solely two local measurements. Our method is also robust against noises and other imperfections, as reflected by our experimental implementation of these tools to verify the entanglement structure of five different eight-photon entangled states. In particular, we demonstrate how their entanglement structure can be precisely and systematically inferred from the experimental measurement of these witnesses. In achieving this goal, we also illustrate how the same set of data can be classically postprocessed to learn the most about the measured system.
Abstract
Quantum key distribution (QKD) enables secure key exchanges between two remote users. The ultimate goal of secure communication is to establish a global quantum network. The existing field ...tests suggest that quantum networks are feasible. To achieve a practical quantum network, we need to overcome several challenges including realizing versatile topologies for large scales, simple network maintenance, extendable configuration and robustness to node failures. To this end, we present a field operation of a quantum metropolitan-area network with 46 nodes and show that all these challenges can be overcome with cutting-edge quantum technologies. In particular, we realize different topological structures and continuously run the network for 31 months, by employing standard equipment for network maintenance with an extendable configuration. We realize QKD pairing and key management with a sophisticated key control centre. In this implementation, the final keys have been used for secure communication such as real-time voice telephone, text messaging and file transmission with one-time pad encryption, which can support 11 pairs of users to make audio calls simultaneously. Combined with intercity quantum backbone and ground–satellite links, our metropolitan implementation paves the way toward a global quantum network.
Mo2C, the newly synthesized MXene with a large lateral size and superconductivity property, has attracted increasing interest in material science. Employing first-principles density functional ...calculations, its intrinsic structural, electrical, thermal, and mechanical properties are investigated in this work. It is found that this MXene is nonmagnetic with a small molar volume. The electrical conductivity is predicted in the order of 106 Ω–1m–1, and its value is significantly influenced by doping. For thermal conductivity, both of the electron and phonon contributions are studied. At room temperature, the Mo2C’s thermal conductivity is determined to be 48.4 Wm–1 K–1, which can be further enhanced by increasing temperature and introducing n-type dopants. The specific heat and thermal expansion coefficient are also assessed, and their values at room temperature are calculated as 290 Jkg–1 K–1 and 2.26 × 10–6 K–1, respectively. Moreover, the thermal contraction of the MXene is found at low temperatures. Under biaxial strains, the elastic modulus is predicted as 312 ± 10 GPa, and the ideal strength is determined to be 20.8 GPa at a critical strain of 0.086. In view of the small molar volume, superhigh electrical conductivity, favorable thermal conductivity, low thermal expansion coefficient, and high mechanical strength, the Mo2C MXene generally merits more widespread applications besides superconductors, such as applying to substrates for other layer materials, and candidate materials for batteries and supercapacitors.
Secret Sharing of a Quantum State Lu, He; Zhang, Zhen; Chen, Luo-Kan ...
Physical review letters,
2016-Jul-15, Letnik:
117, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Secret sharing of a quantum state, or quantum secret sharing, in which a dealer wants to share a certain amount of quantum information with a few players, has wide applications in quantum ...information. The critical criterion in a threshold secret sharing scheme is confidentiality: with less than the designated number of players, no information can be recovered. Furthermore, in a quantum scenario, one additional critical criterion exists: the capability of sharing entangled and unknown quantum information. Here, by employing a six-photon entangled state, we demonstrate a quantum threshold scheme, where the shared quantum secrecy can be efficiently reconstructed with a state fidelity as high as 93%. By observing that any one or two parties cannot recover the secrecy, we show that our scheme meets the confidentiality criterion. Meanwhile, we also demonstrate that entangled quantum information can be shared and recovered via our setting, which shows that our implemented scheme is fully quantum. Moreover, our experimental setup can be treated as a decoding circuit of the five-qubit quantum error-correcting code with two erasure errors.
MXenes have attracted intensive attention because of their widespread applications. As a well-studied member of the MXene family, Ti2CO2 has been demonstrated to be semiconducting with ultrahigh ...carrier mobility, acting as a candidate material for electronic devices. In this work, the influence of layer thickness on the electrical conductivity of Ti2CO2 is investigated combined with first-principles density functional calculations and the Boltzmann transport theory. Because of the layer interaction-induced band splitting, the band gap of Ti2CO2 generally decreases with increasing layers. Based on the generalized gradient approximation, the band gap in monolayer Ti2CO2 is determined to be 0.260 eV, which decreases to 0.0369 eV in the five-layer configuration. Further, the strain influence on the electronic structure of the multilayer Ti2CO2 is studied. With increasing compression strains perpendicular to the basal plane, the configuration is found to transform from a semiconductor to a semimetal, then to a semiconductor, and at last to a metal. This result implies that the electronic property of the multilayer Ti2CO2 can be efficiently manipulated by strain and that the multilayer configurations could be applied in strain sensors. Moreover, our work may open a door to realize bulk semiconductors through compression of accordion-like multilayer MXenes.
Antibodies with ontogenies from VH1-2 or VH1-46-germline genes dominate the broadly neutralizing response against the CD4-binding site (CD4bs) on HIV-1. Here, we define with longitudinal sampling ...from time-of-infection the development of a VH1-46-derived antibody lineage that matured to neutralize 90% of HIV-1 isolates. Structures of lineage antibodies CH235 (week 41 from time-of-infection, 18% breadth), CH235.9 (week 152, 77%), and CH235.12 (week 323, 90%) demonstrated the maturing epitope to focus on the conformationally invariant portion of the CD4bs. Similarities between CH235 lineage and five unrelated CD4bs lineages in epitope focusing, length-of-time to develop breadth, and extraordinary level of somatic hypermutation suggested commonalities in maturation among all CD4bs antibodies. Fortunately, the required CH235-lineage hypermutation appeared substantially guided by the intrinsic mutability of the VH1-46 gene, which closely resembled VH1-2. We integrated our CH235-lineage findings with a second broadly neutralizing lineage and HIV-1 co-evolution to suggest a vaccination strategy for inducing both lineages.
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•Developmental pathway of a CD4-mimicking antibody lineage from time of infection•Maturation involves focused recognition of CD4-binding site of vulnerability•Intrinsic VH1-46 gene mutability guides somatic mutation of CD4-binding site bnAbs•Study provided a strategy for inducing both CD4-mimicking and CDR H3-using bnAbs
The complete life history of an HIV-1 broadly neutralizing antibody lineage, from the time of infection through development of its full potency and breadth, reveals key features that are common between HIV-1 antibodies from unrelated donors and that can be exploited to induce similar antibodies with vaccines.
Using first-principles calculations, the electronic structures and electron transport properties of zigzag and armchair O-functionalized Ti2C MXene nanoribbons are examined in this work. We ...demonstrate that the energy gaps in patterned Ti2CO2 nanoribbons can be tuned by appropriate designs of crystallographic orientation and widths. The Ti2CO2 nanoribbons along the zigzag direction with width parameter larger than six show zero or very low band gaps, while band gaps are opened for Ti2CO2 nanoribbons with armchair-shaped edges. The electronic transport properties for the devices of Ti2CO2 nanoribbons with various widths are investigated using nonequilibrium Green’s functions, and the current–voltage characteristics of the devices are predicted. The current calculations reveal that some of these devices may have a nonlinear feature as well as negative differential resistance behaviors. The zigzag and armchair Ti2CO2 nanoribbon devices show different current–voltage curves. There are onset biases for armchair Ti2CO2 nanoribbons so that the current is generated due to the band gaps but not for most of the zigzag nanoribbons. The corresponding mechanisms for the variation of electronic band gaps and electronic transport properties are discussed. Based on their excellent carrier mobilities reported for the Ti2CO2 MXene and the negative differential resistance effect found in this work, the Ti2CO2 nanoribbon systems might find promising applications in nanoelectronic devices.
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