Fabrication of rhenium Josephson junctions

Rhenium is a superconductor with a relatively weak tendency to oxidize, which is advantageous in superconducting quantum circuit and qubit applications. In this work, Re/A1-A1Ox/Re Josephson tunnel junctions were fabricated using a selective film-etching process similar to that developed in Nb trilayer technology. The Re films had a superconducting transition temperature of 4.8 K and a transition width of 0.2 K. The junctions were found to be highly reproducible using the fabrication process and their characteristics had good quality with a low leakage current and showed a superconducting gap of 0.55 meV.     

富氮掺杂碳空心纳米笼协同钴镍硫化物提升超级电容器性能

采用简单的热解-硫化两步法成功制备了一种新型的富氮掺杂碳空心纳米笼(NC)负载双元金属硫化物纳米颗粒(CoNi_xS_y)的复合材料 CoNi_xS_y/NC。该策略以丁二酮肟镍为镍源,增加了活性位点,同时前驱体 ZIF-8@Ni-ZIF-67的核壳结构为空心碳纳米笼的构建提供了可能性。这种独特的负载多金属硫化物纳米颗粒的中空结构使CoNi_xS_y/NC作为电极材料时具有更多的活性位点、更高的导电性和结构稳定性,从而使其具有较高的比容量(1 A·g^-1时比容量为629.2 F·g^-1),优异的循环稳定性(1 A·g^-1下1 000次循环测试后容量保持率为93.4%)。当将其进一步组装成对称超级电容器后,在1 A·g^-1下可提供207.2 F·g^-1的比电容,1 000圈循环稳定后的容量保持率为85.36%。     

Measuring Loschmidt echo via Floquet engineering in superconducting circuits

The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.     

Fabrication of high-quality submicron Nb/Al--AlOx/Nb tunnel junctions

Nb/Al-AlOx/Nb tunnel junctions are often used in the studies of macroscopic quantum phenomena and superconducting qubit applications of the Josephson devices. In this work, we describe a convenient and reliable process using electron beam lithography for the fabrication of high-quality, submicron-sized Nb/Al-AlOx/Nb Josephson junctions. The technique follows the well-known selective Nb etching process and produces high-quality junctions with Vm=100 mV at 2.3 K for the typical critical current density of 2.2 kA/cm^2, which can be adjusted by controlling the oxygen pressure and oxidation time during the formation of the tunnelling barrier. We present the results of the temperature dependence of the sub-gap current and in-plane magnetic-field dependence of the critical current, and compare them with the theoretical predictions.     

液晶光定向层材料

本文综述了近10年来液晶显示用光定向层材料领域的研究现状和进展情况，主要概述了光降解型、光致异构型、光交联型以及自组装等材料，并对目前报道的液晶光定向机理进行了总结和归纳。     

Nb/Al-AlOx/Nb junctions with controllable critical current density for qubit application

Nb/Al-AlOx/Nb tunnel junctions with controllable critical current density Jc are fabricated using the standard selective Nb etching process.Tunnel barriers are formed in different oxygen exposure conditions (oxygen pressure P and oxidation time t),giving rise to Jc ranging from 100 A/cm2 to above 2000 A/cm2.Jc shows a familiar linear dependence on P × t in logarithmic scales.We calculate the energy levels of the phaseand flux-type qubits using the achievable junction parameters and show that the fabricated Nb/Al-AlOx/Nb tunnel junctions can be used conveniently for quantum computation applications in the future.     

木质素接枝偶氮苯液晶聚合物的合成与表征及光响应性能研究

以天然高分子木质素为原料,通过亲核取代反应将木质素改性成为大分子引发剂,引发偶氮苯单体的原子转移自由基聚合(ATRP),得到一系列木质素基光响应聚合物.接枝后的木质素的热稳定性明显改善,且平均接枝率达到72.8%时才能表现出液晶行为.小角X射线散射和偏光显微镜的结果表明所形成的液晶相为近晶C型,层间距为3.21nm.在此基础上,用紫外-可见吸收光谱(UV-Vis)对木质素基液晶聚合物的光响应性进行研究,发现溶液中的光响应性比膜状态的光响应速率快.在紫外光的辐照下,木质素基液晶聚合物表现出快速的光致液晶-各向同性相变行为.     

High quality factor superconducting coplanar waveguide fabricated with TiN

We fabricated TiN coplanar waveguides using standard lithography techniques followed by ICP etch. In order to achieve high quality factor, we investigated the film growth by choosing different deposition conditions for various substrates. Quality factors of waveguide resonators were measured at 20 mK in both high and low microwave power limits. An inner quality factor of several million was achieved at high power limit for a predominantly(200)-oriented TiN film which was grown on HF cleaned silicon wafer. A quality factor of larger than one million was achieved at high power limit for TiN film grown on sapphire.