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A quantum access network

Axel Dahlberg, Stephanie Wehner
Stabilizer states form an important class of states in quantum information, and are of central importance in quantum error correction. Here, we provide an algorithm for deciding whether one stabilizer (target) state can be obtained from another stabilizer (source) state by single-qubit Clifford operations (LC), single-qubit Pauli measurements (LPM) and classical communication (CC) between sites holding the individual qubits. What is more, we provide a recipe to obtain the sequence of LC+LPM+CC operations which prepare the desired target state from the source state, and show how these operations can be applied in parallel to reach the target state in constant time...
July 13, 2018: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Rikizo Ikuta, Toshiki Kobayashi, Tetsuo Kawakami, Shigehito Miki, Masahiro Yabuno, Taro Yamashita, Hirotaka Terai, Masato Koashi, Tetsuya Mukai, Takashi Yamamoto, Nobuyuki Imoto
Long-lifetime quantum storages accessible to the telecom photonic infrastructure are essential to long-distance quantum communication. Atomic quantum storages have achieved subsecond storage time corresponding to 1000 km transmission time for a telecom photon through a quantum repeater algorithm. However, the telecom photon cannot be directly interfaced to typical atomic storages. Solid-state quantum frequency conversions fill this wavelength gap. Here we report on the experimental demonstration of a polarization-insensitive solid-state quantum frequency conversion to a telecom photon from a short-wavelength photon entangled with an atomic ensemble...
May 21, 2018: Nature Communications
Yunfei Pu, Yukai Wu, Nan Jiang, Wei Chang, Chang Li, Sheng Zhang, Luming Duan
A quantum interface links the stationary qubits in a quantum memory with flying photonic qubits in optical transmission channels and constitutes a critical element for the future quantum internet. Entanglement of quantum interfaces is an important step for the realization of quantum networks. Through heralded detection of photon interference, we generate multipartite entanglement between 25 (or 9) individually addressable quantum interfaces in a multiplexed atomic quantum memory array and confirm genuine 22-partite (or 9-partite) entanglement...
April 2018: Science Advances
Yexin Feng, Zhichang Wang, Jing Guo, Ji Chen, En-Ge Wang, Ying Jiang, Xin-Zheng Li
Proton tunneling is an elementary process in the dynamics of hydrogen-bonded systems. Collective tunneling is known to exist for a long time. Atomistic investigations of this mechanism in realistic systems, however, are scarce. Using a combination of ab initio theoretical and high-resolution experimental methods, we investigate the role played by the protons on the chirality switching of a water tetramer on NaCl(001). Our scanning tunneling spectroscopies show that partial deuteration of the H2 O tetramer with only one D2 O leads to a significant suppression of the chirality switching rate at a cryogenic temperature (T), indicating that the chirality switches by tunneling in a concerted manner...
March 14, 2018: Journal of Chemical Physics
Kai Yang, Yujeong Bae, William Paul, Fabian D Natterer, Philip Willke, Jose L Lado, Alejandro Ferrón, Taeyoung Choi, Joaquín Fernández-Rossier, Andreas J Heinrich, Christopher P Lutz
Quantum spin networks having engineered geometries and interactions are eagerly pursued for quantum simulation and access to emergent quantum phenomena such as spin liquids. Spin-1/2 centers are particularly desirable, because they readily manifest coherent quantum fluctuations. Here we introduce a controllable spin-1/2 architecture consisting of titanium atoms on a magnesium oxide surface. We tailor the spin interactions by atomic-precision positioning using a scanning tunneling microscope (STM) and subsequently perform electron spin resonance on individual atoms to drive transitions into and out of quantum eigenstates of the coupled-spin system...
December 1, 2017: Physical Review Letters
Xun Gao, Lu-Ming Duan
Part of the challenge for quantum many-body problems comes from the difficulty of representing large-scale quantum states, which in general requires an exponentially large number of parameters. Neural networks provide a powerful tool to represent quantum many-body states. An important open question is what characterizes the representational power of deep and shallow neural networks, which is of fundamental interest due to the popularity of deep learning methods. Here, we give a proof that, assuming a widely believed computational complexity conjecture, a deep neural network can efficiently represent most physical states, including the ground states of many-body Hamiltonians and states generated by quantum dynamics, while a shallow network representation with a restricted Boltzmann machine cannot efficiently represent some of those states...
September 22, 2017: Nature Communications
Yao Xing, Chenyang Shi, Jianhui Zhao, Wu Qiu, Naibo Lin, Jingjuan Wang, Xiao Bing Yan, Wei Dong Yu, Xiang Yang Liu
Silk fibroin (SF) offers great opportunities in manufacturing biocompatible/partially biodegradable devices with environmental benignity and biomedical applications. To obtain active SF devices of next generation, this work is to demonstrate a new functionalization strategy of the mesoscopic functionalization for soft materials. Unlike the atomic functionalization of solid materials, the meso-functionalization is to incorporate meso-dopants, i.e., functional molecules or nanomaterials, quantum dots, into the mesoscopic networks of soft materials...
September 1, 2017: Small
Lukas Schlipf, Thomas Oeckinghaus, Kebiao Xu, Durga Bhaktavatsala Rao Dasari, Andrea Zappe, Felipe Fávaro de Oliveira, Bastian Kern, Mykhailo Azarkh, Malte Drescher, Markus Ternes, Klaus Kern, Jörg Wrachtrup, Amit Finkler
Scalable quantum technologies require an unprecedented combination of precision and complexity for designing stable structures of well-controllable quantum systems on the nanoscale. It is a challenging task to find a suitable elementary building block, of which a quantum network can be comprised in a scalable way. We present the working principle of such a basic unit, engineered using molecular chemistry, whose collective control and readout are executed using a nitrogen vacancy (NV) center in diamond. The basic unit we investigate is a synthetic polyproline with electron spins localized on attached molecular side groups separated by a few nanometers...
August 2017: Science Advances
Zongyuan Liu, Carl O Trindle, Quanli Gu, Wei Wu, Peifeng Su
The neutral and cationic forms of tryptamine-water dimer present a variety of noncovalent interactions. To characterize these interactions, a series of complementary methods, including the quantum theory of atoms in molecules, noncovalent interaction plots, natural bond orbital analysis, and energy decomposition analysis, were used. For the first time, the existence of the three intermolecular H-bonds in the conformer-locked tryptamine-water dimer A-H2O are identified, highlighting a single water's role as one proton donor and two proton acceptors as it binds to tryptamine...
September 27, 2017: Physical Chemistry Chemical Physics: PCCP
Johannes Loehr, Daniel de Las Heras, Michael Loenne, Jonas Bugase, Adam Jarosz, Maciej Urbaniak, Feliks Stobiecki, Andreea Tomita, Rico Huhnstock, Iris Koch, Arno Ehresmann, Dennis Holzinger, Thomas M Fischer
The topologically protected transport of colloidal particles on top of periodic magnetic patterns is studied experimentally, theoretically, and with computer simulations. To uncover the interplay between topology and symmetry we use patterns of all possible two dimensional magnetic point group symmetries with equal lengths lattice vectors. Transport of colloids is achieved by modulating the potential with external, homogeneous but time dependent magnetic fields. The modulation loops can be classified into topologically distinct classes...
July 26, 2017: Soft Matter
Romain Dupuis, Jorge S Dolado, Magali Benoit, Jose Surga, Andrés Ayuela
Studies of the structure of hydroxides under pressure using neutron diffraction reveal that the high concentration of hydrogen is distributed in a disordered network. The disorder in the hydrogen-bond network and possible phase transitions are reported to occur at pressures within the range accessible to experiments for layered calcium hydroxides, which are considered to be exemplary prototype materials. In this study, the static and dynamical properties of these layered hydroxides are investigated using a quantum approach describing nuclear motion, shown herein to be required particularly when studying diffusion processes involving light hydrogen atoms...
July 7, 2017: Scientific Reports
G Harder, V Ansari, T J Bartley, B Brecht, C Silberhorn
In the last few decades, there has been much progress on low loss waveguides, very efficient photon-number detectors and nonlinear processes. Engineered sum-frequency conversion is now at a stage where it allows operation on arbitrary temporal broadband modes, thus making the spectral degree of freedom accessible for information coding. Hereby the information is often encoded into the temporal modes of a single photon. Here, we analyse the prospect of using multi-photon states or squeezed states in different temporal modes based on integrated optics devices...
August 6, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Masahide Sasaki, Hiroyuki Endo, Mikio Fujiwara, Mitsuo Kitamura, Toshiyuki Ito, Ryosuke Shimizu, Morio Toyoshima
Quantum communication and quantum cryptography are expected to enhance the transmission rate and the security (confidentiality of data transmission), respectively. We study a new scheme which can potentially bridge an intermediate region covered by these two schemes, which is referred to as quantum photonic network. The basic framework is information theoretically secure communications in a free space optical (FSO) wiretap channel, in which an eavesdropper has physically limited access to the main channel between the legitimate sender and receiver...
August 6, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Y-F Pu, N Jiang, W Chang, H-X Yang, C Li, L-M Duan
To realize long-distance quantum communication and quantum network, it is required to have multiplexed quantum memory with many memory cells. Each memory cell needs to be individually addressable and independently accessible. Here we report an experiment that realizes a multiplexed DLCZ-type quantum memory with 225 individually accessible memory cells in a macroscopic atomic ensemble. As a key element for quantum repeaters, we demonstrate that entanglement with flying optical qubits can be stored into any neighboring memory cells and read out after a programmable time with high fidelity...
May 8, 2017: Nature Communications
Yevgeni Dudko, Estie Kruger, Marc Tennant
INTRODUCTION: Australia is one of the least densely populated countries in the world, with a population concentrated on or around coastal areas. Up to 33% of the Australian population are likely to have untreated dental decay, while people with inadequate dentition (fewer than 21 teeth) account for up to 34% of Australian adults. Historically, inadequate access to public dental care has resulted in long waiting lists, received much media coverage and been the subject of a new federal and state initiative...
January 2017: Rural and Remote Health
X-Y Chang, D-L Deng, X-X Yuan, P-Y Hou, Y-Y Huang, L-M Duan
To construct a quantum network with many end users, it is critical to have a cost-efficient way to distribute entanglement over different network ends. We demonstrate an entanglement access network, where the expensive resource, the entangled photon source at the telecom wavelength and the core communication channel, is shared by many end users. Using this cost-efficient entanglement access network, we report experimental demonstration of a secure multiparty computation protocol, the privacy-preserving secure sum problem, based on the network quantum cryptography...
2016: Scientific Reports
Jiri Brus, Libor Kobera, Martina Urbanova, Barbora Doušová, Miloslav Lhotka, David Koloušek, Jiří Kotek, Pavel Čuba, Jiri Czernek, Jiří Dědeček
Nanostructured materials typically offer enhanced physicochemical properties because of their large interfacial area. In this contribution, we present a comprehensive structural characterization of aluminosilicate hybrids with polymer-conjugated nanosized zeolites specifically grown at the organic-inorganic interface. The inorganic amorphous Al-O-Si framework is formed by alkali-activated low-temperature transformation of metakaoline, whereas simultaneous copolymerization of organic comonomers creates a secondary epoxide network covalently bound to the aluminosilicate matrix...
March 22, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Bernd Fröhlich, James F Dynes, Marco Lucamarini, Andrew W Sharpe, Simon W-B Tam, Zhiliang Yuan, Andrew J Shields
Optical access networks connect multiple endpoints to a common network node via shared fibre infrastructure. They will play a vital role to scale up the number of users in quantum key distribution (QKD) networks. However, the presence of power splitters in the commonly used passive network architecture makes successful transmission of weak quantum signals challenging. This is especially true if QKD and data signals are multiplexed in the passive network. The splitter introduces an imbalance between quantum signal and Raman noise, which can prevent the recovery of the quantum signal completely...
2015: Scientific Reports
Gerhard Sohr, Nina Ciaghi, Michael Schauperl, Klaus Wurst, Klaus R Liedl, Hubert Huppertz
To date, the access to the substance class of borates containing nitrogen, for example, nitridoborates, oxonitridoborates, or amine borates, was an extreme effort owing to the difficult starting materials and reaction conditions. Although a number of compounds containing boron and nitrogen are known, no adduct of ammonia to an inorganic borate has been observed so far. A new synthetic approach starting from the simple educts CdO, B2O3, and aqueous ammonia under conditions of 4.7 GPa and 800 °C led to the synthesis of Cd(NH3)2[B3O5(NH3)]2 as the first ammine borate...
May 18, 2015: Angewandte Chemie
Robert G McAllister, Lars Konermann
Many protein structural investigations involve the use of H/D exchange (HDX) techniques. It is commonly thought that amide backbone protection arises from intramolecular H-bonding and/or burial of NH sites. Recently, fundamental HDX-related tenets have been called into question. The current work focuses on ubiquitin for exploring the defining features that distinguish amides in "open" (exchange-competent) and "closed" (exchange-incompetent) environments. Instead of relying on static X-ray structures, we employ all-atom molecular dynamics (MD) simulations for obtaining a dynamic view of the protein ground state and its surrounding solvent...
April 28, 2015: Biochemistry
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