Of crucial importance for the application of high temperature superconducting coated conductors (CCs) is the delamination strength due to thermal stress and Lorentz force during their operation. This paper reports the mechanical delamination strengths of YBCO CCs at room temperature and 77 K, as well as the electro-mechanical delamination strength form a modified anvil tensile method. Compared to previous measurement setups, our anvil device only has one degree of freedom of transverse tension. Moreover, we use a vertical soldering technique to ensure the data reliability. Since we eliminate the influence of the measurement method on the experimental results, a naturally discrete property of the delamination strength is obtained. To describe these experimental data, a three-parameter Weibull distribution function has been suggested and a new criterion for determining delamination strength is proposed from the reliability function, which can be conveniently referred to for engineering design.

The second generation HTS wires have been used in many superconducting components of electrical engineering after they were fabricated. New challenge what we face to is how the damages occur in such wires with multi-layer structure under both mechanical and extreme environment, which also dominates their quality. In this work, a macroscale technique combined a real-time magneto-optical imaging with a cryogenic uniaxial-tensile loading system was established to investigate the damage behavior accompanied with magnetic flux evolution. Under a low speed of tensile strain, it was found that the local magnetic flux moves gradually to form intermittent multi-stack spindle penetrations, which corresponds to the cracks initiated from substrate and extend along both tape thickness and width directions, where the amorphous phases at the tip of cracks were also observed. The obtained results reveal the mechanism of damage formation and provide a potential orientation for improving mechanical quality of these wires.

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The orbital angular momentum (OAM) of photons is a promising degree of freedom for high-dimensional quantum key distribution (QKD). However, effectively mitigating the adverse effects of atmospheric turbulence is a persistent challenge in OAM QKD systems operating over free-space communication channels. In contrast to previous works focusing on correcting static simulated turbulence, we investigate the performance of OAM QKD in real atmospheric turbulence with real-time adaptive optics (AO) correction. We show that, even our AO system provides a limited correction, it is possible to mitigate the errors induced by weak turbulence and establish a secure channel. The crosstalk induced by turbulence and the performance of AO systems are investigated in two configurations: a lab-scale link with controllable turbulence, and a 340 m long cross-campus link with dynamic atmospheric turbulence. Our experimental results suggest that an advanced AO system with fine beam tracking, reliable beam stabilization, precise wavefront sensing, and accurate wavefront correction is necessary to adequately correct turbulence-induced error. We also propose and demonstrate different solutions to improve the performance of OAM QKD with turbulence, which could enable the possibility of OAM encoding in strong turbulence. IntroductionQuantum key distribution (QKD), which assures unconditionally secure communication between multiple parties, is one of the most promising and encouraging applications of quantum physics [1][2][3]. Instead of relying on mathematical complexity, the security of QKD is guaranteed by fundamental physical laws, which indicate that the encrypted keys will remain secure even against eavesdroppers with unlimited computation power [1-3].Since its birth in 1984 [4], the concepts of QKD have been demonstrated in various platforms, including fiber-based networks [5,6], free-space communication links [7,8], underwater [9,10] and over-marine channels [11,12]. However, in most QKD systems, the information is encoded in the polarization degree of freedom, which is a two-dimensional Hilbert space limiting the information capacity to 1 bit per photon. Even through a single-photon source with a high brightness has been developed [13,14], the two-dimensional QKD systems are still photon-inefficient.As a comparison, high-dimensional QKD systems are more photon-efficient and robust to eavesdropping [15][16][17]. In recent decades, many new protocols involving high-dimensional encoding have emerged. Encoding information with orbital angular momentum (OAM) states, which can span an infinite-dimensional Hilbert space, has been experimentally demonstrated arXiv:2002.08884v1 [eess.SP] 14 Feb 2020 to be advantageous in both high-dimensional quantum cryptography [18][19][20][21][22] and classical communication [23,24]. By definition, an OAM state | carrying units of OAM has intertwined helical wavefronts, where denotes the OAM quantum number and is an integer [25]. While efficient and high-fidelity fibers for high-order spatial modes are und...

Anisotropic density-near-zero (ADNZ) metamaterials, with only one component of the mass density tensor near zero, have been proposed and used to manipulate the flow of the acoustic energy in designed paths. In the inhomogeneous ADNZ metamaterials, a strong averaging effect on the non-zero component of the mass density tensor is theoretically and numerically demonstrated. Based on this effect, the acoustic intensity vector, which represents the average direction and magnitude of the acoustic energy flow, can be manipulated by simply designing the spatial profile of the non-zero mass density component. This method provides more possibilities in controlling the acoustic intensity in almost an arbitrary way.