Proposal for optical parity state re-encoder

We propose a re-encoder to generate a refreshed parity encoded state from an existing parity encoded state. This is the simplest case of the scheme by Gilchrist et al. [Phys. Rev. A 2007 75, 052328]. We give a detailed experimental arrangement for the re-encoder and show that it is possible to experimentally demonstrate with existing technology parity encoded quantum gates and teleportation.     

Quantum encoder and decoder for practical quantum key distribution using a planar lightwave circuit

To launch quantum key distribution (QKD) into the commercial market, it is important to develop a system that is simpler and more reliable using current technology. This report proposes quantum encoders and decoders using a passive planar lightwave circuit (PLC) that is useful for implementing optical-fiber-based QKD systems. Our encoders and decoders are based on an asymmetric Mach–Zehnder interferometer and allow us to prepare and analyze various photonic time-bin qubits reliably. The system can be stable and polarization-insensitive merely by stabilizing and controlling the device temperature. Our PLC-based devices enables us to simplify the QKD system and increase its reliability.     

Measurement-device-independent quantum key distribution with odd coherent state

Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all the detection attacks, thus when it is combined with the decoy-state method, the final key rate can be obtained by estimating the gain and quantum bit error rate for various input photon numbers. In this paper, we propose to perform MDI-QKD with odd coherent state (OCS) and compare the results with weak coherent source scenario. Our simulation indicates that both the secure key rate and transmission distance can be improved evidently with OCS owing to the lower probability of multi-photon events of the OCS. Furthermore, we apply the finite key analysis to the decoy-state MDI-QKD with OCS and obtain a practical key rate.     

The QKD network: model and routing scheme

Quantum key distribution (QKD) technology can establish unconditional secure keys between two communicating parties. Although this technology has some inherent constraints, such as the distance and point-to-point mode limits, building a QKD network with multiple point-to-point QKD devices can overcome these constraints. Considering the development level of current technology, the trust relaying QKD network is the first choice to build a practical QKD network. However, the previous research didn’t address a routing method on the trust relaying QKD network in detail. This paper focuses on the routing issues, builds a model of the trust relaying QKD network for easily analysing and understanding this network, and proposes a dynamical routing scheme for this network. From the viewpoint of designing a dynamical routing scheme in classical network, the proposed scheme consists of three components: a Hello protocol helping share the network topology information, a routing algorithm to select a set of suitable paths and establish the routing table and a link state update mechanism helping keep the routing table newly. Experiments and evaluation demonstrates the validity and effectiveness of the proposed routing scheme.     

Asynchronous quantum key distribution on a relay network

We show how quantum key distribution on a multi-user, multi-path, network can be used to establish a key between any two end-users in an asynchronous fashion using the technique of bit-transport. By a suitable adaptation of our previous secret-sharing scheme we show that an attacker has to compromise all of the intermediate relays on the network in order to obtain the key. Thus, two end-users can establish a secret key provided they trust at least one of the network relays.     

Free-space communication through turbulence: a comparison of plane-wave and orbital-angular-momentum encodings

Abstract

Free-space communication allows one to use spatial mode encoding, which is susceptible to the effects of diffraction and turbulence. Here, we discuss the optimum communication modes of a system while taking such effects into account. We construct a free-space communication system that encodes information onto the plane-wave (PW) modes of light. We study the performance of this system in the presence of atmospheric turbulence, and compare it with previous results for a system employing orbital-angular-momentum (OAM) encoding. We are able to show that the PW basis is the preferred basis set for communication through atmospheric turbulence for a system with a large Fresnel number product. This study has important implications for high-dimensional quantum key distribution systems.     

Nonclassical photon statistics in a single nickel–nitrogen diamond color center photoluminescence at room temperature

The photoluminescence of a single nickel–nitrogen NE8 color center in a diamond nanocrystal is investigated at room temperature under pulsed excitation by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of the temporal intensity correlation function. Antibunching at short times and bunching behavior for longer times is observed, associated with sub- and super-Poissonian statistics, respectively. The behavior is interpreted by a ‘on–off’ state model, and transition rates between these two states are inferred from intensity correlation measurements realized at different excitation powers. NE8 color center photoluminescence quantum yield is evaluated to be 65%, a value higher than achieved for a nitrogen-vacancy color center, which is, up to now, the most practical single emitter to build a reliable single-photon source at room temperature.     

Proposal for a new magnet lattice for an electron storage ring for a high brightness synchrotron radiation source

A new magnet lattice, named “variable emittance”, for an electron storage ring dedicated to synchrotron radiation is proposed. The lattice has a high flexibility to meet the requirements for a high performance undulator as well as for conventional synchrotron radiation from a bending magnet. Tune shifts due to magnet imperfections were simulated and it is found that the periodic solution of the optics is stable enough except for a very high tune region. The effects of undulators and wigglers on the stored beam were studied and a correction for the tune shift is found necessary for high field wigglers.     

Phase-encoded measurement device independent quantum key distribution without a shared reference frame

In this paper, a phase-encoded measurement device independent quantum key distribution (MDI-QKD) protocol without a shared reference frame is presented, which can generate secure keys between two parties while the quantum channel or interferometer introduces an unknown and slowly time-varying phase. The corresponding secret key rate and single photons bit error rate is analysed, respectively, with single photons source (SPS) and weak coherent source (WCS), taking finite-key analysis into account. The numerical simulations show that the modified phase-encoded MDI-QKD protocol has apparent superiority both in maximal secure transmission distance and key generation rate while possessing the improved robustness and practical security in the high-speed case. Moreover, the rejection of the frame-calibrating part will intrinsically reduce the consumption of resources as well as the potential security flaws of practical MDI-QKD systems.     

Proposal of a new concept on creep fracture remnant life for a precracked specimen

Abstract

The creep life time of a smooth specimen can be predicted using existing laws for creep deformation and steady state creep rate. When crack growth behaviour is involved, it is necessary to construct a law of creep crack growth rate to predict creep fracture life. Creep fracture life can be measured by integrating the law of creep crack growth rate. One example is the creep crack growth rate, represented by the parameter Q*. In this study, we investigated the applicability of this prediction method to creep fracture remnant life for a cracked specimen. The Ω criterion is proposed to predict creep fracture remnant life for a smooth specimen for creep ductile materials. In this study, the correlation between Q*_L derived from the paremeters Q* and Ω is investigated. The correlation between Q_L* and Ω provided a unified theoretical prediction law of creep fracture remnant life for high-temperature creep-ductile materials in the range from smooth to precracked specimens.     

A new method for the solution of three dimensional magnetostatic fields, using a scalar potential

A new method "Equivalent Magnetized Region Solution" based on scalar potential for solving 3D magnetostatic fields is presented. The current distribution is transformed into a region of magnetic dipoles and only one scalar potential is used to calculate the field. A program "CMF3D" has been developed by finite element method, equipped with program "MESH" for subdividing field region into elements. Three examples by the solution are presented and compared with results from analytical method or experiment.     

新型聚酯材料状态方程的研究

聚酯材料在航空航天领域有着较广泛的应用,其高压力学性能的研究逐渐受到人们的关注。针对一种新型聚酯材料通过轻气炮(LGG)实验开展其冲击压缩力学性能研究。采用非对称碰撞直接测量法测量并计算激波速度(D)与波后质点速度(u)的D-u型Hugoniot曲线,并由此推导出P-η型Hugoniot曲线。建立了该材料的Murnagham状态方程,求得了相应的材料参数。并对新型聚酯材料的Murnagham状态方程和P-η型Hugoniot状态方程进行了比较和分析。     

Compact stranded superconducting conductors with both low ac loss and high stability. I. Proposal of a new design

A new method for designing compact stranded superconducting conductors is proposed as a solution to the dilemma that low loss and high stability cannot be simultaneously attained in the commonly used conductors. In our design, the twist directions of the conductor and those of the sub-cables in it are the same. In addition, the twist pitch of the sub-cables is relatively longer than that of the conductor. The sub-cables crossover each other in the conductor. Under the changing transverse magnetic fields oriented perpendicular to the broad face of the conductor, the induced voltages between the above-mentioned crossover sub-cables become small, so inter-sub-cable coupling losses are decreased. As a result, not only the total coupling loss in the conductor is decreased, but also high stability is maintained due to the low contact resistance between the sub-cables. Our method theoretically indicates such high performance as attaining both low ac loss and high stability. An example of our design is shown for a large-scale compact stranded superconducting conductor.     

Direct sequence voice scrambling scheme‐a new technique for secure communications

Abstract

Communication security is getting more and more important. Although the encryption of digitized speech is very attractive, direct scrambling of the analog speech waveforms continues to be an important approach due to a strong desire for the use of existing telephone networks with standard telephone bandwidth at acceptable speech quality and cost. In this paper, a new approach for analog speech scrambling, a Direct Sequence Voice Scrambling (DSVS) scheme, is proposed, in which the spread spectrum concept is borrowed but combined with a newly developed bandwidth reduction technique. The system design, performance analysis, practical considerations and simulation results are presented in detail in this paper. The analysis indicates that the DSVS scheme can provide the following advantages: small residual intelligibility, high degree of security, small bandwidth expansion, no time delay and only slight degradation of speech quality.     

A new scheme for imposing a minimum length scale in topology optimization

A new scheme for imposing a minimum length scale in topology optimization is presented. It guarantees the existence of an optimal design for a large class of topology optimization problems of practical interest. It is formulated as one constraint that is computationally cheap and for which sensitivities are also cheap to compute. The constraint value is ideally zero, but it can be relaxed to a positive value. The effect of the method is illustrated in topology optimization for minimum compliance and design of compliant mechanisms. Notably, the method produces compliant mechanisms with distributed flexibility, something that has previously been difficult to obtain using topology optimization for the design of compliant mechanisms. The term ‘MOLE method’ is suggested for the method. Copyright © 2003 John Wiley & Sons, Ltd.     

Experimental validation of a new semi‐implicit CE–SE scheme for the calculation of unsteady one‐dimensional flow in tapered ducts

This paper presents an improvement in the conservation element–solution element (CE–SE) scheme for calculating one‐dimensional flow through tapered ducts. This new CE–SE scheme has been validated against experiments in tapered ducts with non‐steady flow using pressure impulses. This validation analyses scheme's ability to reproduce instantaneous pressure in time and frequency domains, mass conservation when the section of the duct changes (which was the main drawback of the original CE–SE scheme) and finally computational time. In order to quantify the improvement of the scheme, the calculations have been compared with experimental data and with the results provided by other schemes, such as the original CE–SE or total variation diminishing schemes. This comparison shows important improvements in mass conservation in relation to the original CE–SE and not significant penalties in computational time. Copyright © 2007 John Wiley & Sons, Ltd.     

A finite difference scheme for solving a three‐dimensional heat transport equation in a thin film with microscale thickness

Heat transport at the microscale is of vital importance in microtechnology applications. The heat transport equation is different from the traditional heat diffusion equation since a second‐order derivative of temperature with respect to time and a third‐order mixed derivative of temperature with respect to space and time are introduced. In this study, we develop a finite difference scheme with two levels in time for the three‐dimensional heat transport equation. It is shown by the discrete energy method that the scheme is unconditionally stable. The three‐dimensional implicit scheme is then solved by using a preconditioned Richardson iteration, so that only a tridiagonal linear system is solved each iteration. Numerical results show that the solution is accurate. Copyright © 2001 John Wiley & Sons, Ltd.     

Colloidal templating for producing hollow ZnO shells: Fabrication, growth and electrical properties

Colloidal templating and pulsed laser deposition (PLD) have been combined to fabricate arrays of ordered two-dimensional hollow ZnO shells. Templates were formed by spin-coating colloidal solutions containing monodispersed polymethylmethacrylate (PMMA) beads. The optimum condition for forming templates of ordered two-dimensional geometry was deduced by calculating the radial distribution functions. On templates ZnO films were deposited by a PLD method. Upon annealing ZnO films crystallize into a würtzite structure. The surface morphology of hollow ZnO shells consists of protruding columnar nano-crystallites with no distinct ZnO texture. The electrical properties were measured as a function of annealing temperature. The electrical conductivity increases with increase in annealing temperature. The activation energy was estimated to be 0.7 eV. The change in the electrical properties upon grain growth has been attributed to alteration in the fraction site availability for defect formation at the grain boundaries.     

Development of a new method for making high dynamic range, vector mixer characterisations

Vector network analysers (VNAs) employ static error models that allow for the removal of static instrumentation errors, thereby enabling the accurate measurement of vector scattering parameters for devices under test (DUTs). Since standard VNA error models are inherently based on relative measurements (i.e. either the reflected or transmitted signal is measured relative to the incident signal at the same frequency), they typically do not provide information about the magnitude and phase of the signal that is input into the DUT, or the signal that is transmitted through the DUT into the second receiver. Such information is crucial for VNA measurements of frequency-offsetting DUTs like mixers. In previous papers, the authors demonstrated how the inclusion of an additional bidirectional signal path allows for the absolute vector error correction (AVEC) of a one-port transmitter/receiver module, thereby allowing for the accurate vector measurement of the signals that are flowing into and/or out of the test port. The authors show how the AVEC method can be used to calibrate multi-port systems, thereby allowing for vector measurements of mixer DUTs (MUTs).