具有Washer型输入线圈的超导量子干涉放大器的制备与表征

超导量子干涉仪(SQUID)放大器具有低输入阻抗、低噪声、低功耗等优点, 目前被广泛用于微弱信号的检测领域. 与其他工艺相比, Nb/Al-AlO_x/Nb结构的约瑟夫森结具有相对较高的转变温度(T_c)、高的磁通电压调制系数以及良好的热循环能力、较宽的临界电流范围, 因此是制备SQUID放大器的很好选择. 设计并制作了欠阻尼、过阻尼约瑟夫森结以及具有Washer型输入线圈的单SQUID放大器, 通过在He³制冷机3 K温区下对器件电流-电压特性进行测量, 得到良好的结I-V特性曲线、SQUID调制特性, 初步实现利用SQUID进行放大作用, 并计算了SQUID的电流分辨率. 此项工作对于超导转变边沿传感器读出电路的实现具有重要的意义.     

超导量子干涉器件读出电路中匹配变压器的传输特性研究

在磁通调制超导量子干涉器件(SQUID)的读出电路中, 匹配变压器具有放大信号和阻抗匹配的功能, 是实现SQUID低噪声读出的关键元件. 利用模拟SQUID电路对匹配变压器进行性能测试, 研究了不同绕制匝数变压器的传输特性, 确定最佳绕制匝数比. 在变压器拾取SQUID电压信号的耦合网络中, 研究了不同电容对变压器传输特性的影响, 实现了变压器耦合网络参数的匹配和优化. 室温下匝数比为1:20的匹配变压器在匹配电容C=1μF时, 输出源电压增益为21.2, 带宽范围可达到210 kHz. 最后在基于磁通调制式DC SQUID读出电路中, 对匹配变压器的工作性能进行了评估与验证. 关键词： 超导量子干涉器件读出电路 匹配变压器 低噪声 传输特性     

Multiplexing technology based on SQUID for readout of superconducting transition-edge sensor arrays

Multiplexing technologies based on superconducting quantum interference devices (SQUIDs) are crucial to cryogenic readout of superconducting transition-edge sensor (TES) arrays. Demands for large-scale TES arrays promote the development of multiplexing technologies towards large multiplexing factors and low readout noise. The development of multiplexing technologies also facilitates new applications of TES arrays in a wide range of frequencies. Here we summarize different types of SQUID-based multiplexing technologies including time-division multiplexing, code-division multiplexing, frequency-division multiplexing and microwave SQUID multiplexing. The advances and parameter constraints of each multiplexing technology are also discussed.     

Modulation depth of series SQUIDs modified by Josephson junction area

The superconducting quantum interference device(SQUID) amplifier is widely used in the field of weak signal detection for its low input impedance, low noise, and low power consumption. In this paper, the SQUIDs with identical junctions and the series SQUIDs with different junctions were successfully fabricated. The Nb/Al-AlO_x/Nb trilayer and input Nb coils were prepared by asputtering equipment. The SQUID devices were prepared by a sputtering and the lift-off method.Investigations by AFM, OM and SEM revealed the morphology and roughness of the Nb films and Nb/Al-AlO_x/Nb trilayer.In addition, the current–voltage characteristics of the SQUID devices with identical junction and different junction areas were measured at 2.5 K in the He~3 refrigerator. The results show that the SQUID modulation depth is obviously affected by the junction area. The modulation depth obviously increases with the increase of the junction area in a certain range. It is found that the series SQUID with identical junction area has a transimpedance gain of 58 ? approximately.     

High TcYBa2Cu3O7−δ superconducting transition-edge microbolometers

High T_c superconducting thin film YBa₂Cu₃O_7−δ (YBCO) bolometers have been fabricated on various substrates such as MgO, LaAlO₃, YSZ and Si using laser ablation technique. Performance of these IR bolometers operating with a Joule-Thomson refrigerator has been investigated. Measurements of the responsivity and low frequency noise near T_c in the current biased YBCO bolometers show that reliable devices can be fabricated. Measured noise equivalent power (NEP), for YBCO/YSZ bolometer, reaches 6 × 10⁻¹⁰W/Hz^1/2 at 165 Hz and has a responsivity of 60 V/W with a blackbody source. This performance is comparable to that of the optimized pyroelectric detectors. The characteristics of YBCO films deposited on Si substrates reveal that superconducting thin film multi-elements or focal plane array with silicon integrated readout circuit are feasible. Such bolometers exhibit NEP of 7 × 10⁻⁹W/Hz^1/2, and significant improvement appears possible. Electrical measurements show no noticeable film degradation after the bolometer is exposed to atmosphere for three months.     

Development of 1.3GHz high-T-c rf SQUID

A new high-T_c (HT_c) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HT_c coplanar superconducting resonator and a large-area HT_c superconducting film concentrator. We have achieved in the 1.3GHz HT_c rf SQUID system a minimal flux noise of 2.5×10^{-5}Φ_0/\sqrt{Hz} and a magnetic field sensitivity of 38fT/\sqrt{Hz} in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm^2 substrate is 1.35mm^2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HT_c rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges.     

Tuning rf-SQUID flux qubit system's potential with magnetic flux bias

At an extremely low temperature of 20 mK, we measured loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop (Φ_f) and the small dc-SQUID (Φ_f^cjj), respectively, the potential shape of the system can be fully controlled in situ. Variations of transition step and overlap size in switching current with the barrier flux bias are analyzed, from which we can obtain some relevant device parameters and built up a model to explain the experimental phenomenon.     

含有两个约瑟夫森结的射频SQUID的本征磁通噪声

我们研究了双结射频超导量子干涉器件（rf SQUID）的含时特性，给出了总磁通的动力学方程，并分析了在回滞模式和非回滞模式下的本征磁通噪声。结果显示：两个结的临界电流差别越大则越有助于获得小的本征噪声，在这种情况下，双结rf SQUID的本征磁通噪声会比单结rf SQUID的噪声稍大，但不超过一个数量级。     

多通道心磁系统标定方法研究

在多通道超导量子干涉器件（SQUID）磁探测系统中,磁场电压转换系数（∂ B/∂ V）是系统的一个重要参数由于SQUID器件和读出电路之间不可避免地存在差异性因此对传感器系统进行系统标定（每个通道的单独标定）显得十分重要本文采用（PCB） 板印制圆形线圈对36通道心磁系统进行标定,并与传统的亥姆霍兹方形线圈产生均匀场的标定方法进行比较结果显示PCB圆形线圈的标定结果 在1.46–1.73 pT·mV^-1 之间,亥姆霍兹方形线圈标定的结果大都在1.56–1.64 pT·mV^-1之间,结果基本一致. 关键词： 超导量子干涉器件 磁探测 磁场-电压转换系数 系统标定     

Measurement of frequency noise spectra of frequency-stabilized LD-pumped Nd:YAG laser by using a cavity with separately suspended mirrors

We have developed a frequency stability system for a commercial LD-pumped Nd:YAG laser in a nonplanar ring oscillator geometry (MISER) which is used for our 20-m prototype gravitational wave detector. The frequency of the laser is locked to the rigid cavity resonance frequency, and the relative frequency noise is suppressed down to 3 × 10⁻⁴ Hz/Hz^1/2 the shot-noise limited level at below 1 kHz. We are successful in evaluating the frequency noise level more accurately by means of a separately suspended reirror type cavity (4-m mode-cleaner); the noise level is 2 × 10⁻² Hz/Hz^1/2. As compared to a frequency noise spectrum which is locked to separately suspended mirror type cavities, the frequency noise is lower at a frequency below 400 Hz.     

Numerical analysis of the smart DROS

A digital superconducting quantum interference device (SQUID) has the potential for a very large dynamic range and a very high slew rate. Our concept of the digital SQUID consists of a double relaxation oscillation SQUID (DROS) with the complete flux locked loop (FLL) electronics on one single chip. The key element of the FLL circuitry is a superconducting up-down counter, which supplies the feedback flux to the DROS. In this paper we will concentrate on the numerical simulations of our new 100 MHz smart DROS. In this new design, the quantization unit of the feedback flux, δΦ_fb=52 mΦ₀, was optimized with respect to the flux noise of the DROS. By doing so, the flux slew rate was maximized without compromising the sensitivity. The optimization resulted in a maximum flux slew rate of δΦ_sig/δt=5×10⁶Φ₀/s.     

Performance of dual-band short-or mid-wavelength infrared photodetectors based on InGaAsSb bulk materials and InAs/GaSb superlattices

In this paper,we demonstrate bias-selectable dual-band short-or mid-wavelength infrared photodetectors based on In_(0.24)Ga_(0.76)As_(0.21)Sb_(0.79)bulk materials and InAs/GaSb type-II superlattices with cutoff wavelengths of 2.2μm and 3.6μm,respectively.At 200 K,the short-wave channel exhibits a peak quantum efficiency of 42%and a dark current density of5.93×10~(-5)A/cm~2at 500 mV,thereby providing a detectivity of 1.55×10~(11)cm·Hz~(1/2)/W.The mid-wave channel exhibits a peak quantum efficiency of 31%and a dark current density of 1.22×10~(-3)A/cm~2at-300 mV,thereby resulting in a detectivity of 2.71×10~(10)cm·Hz~(1/2)/W.Moreover,we discuss the band alignment and spectral cross-talk of the dual-band n-i-p-p-i-n structure.     

Development of 1.3GHz high-T-c rf SQUID

A new high-T_c (HT_c) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HT_c coplanar superconducting resonator and a large-area HT_c superconducting film concentrator. We have achieved in the 1.3GHz HT_c rf SQUID system a minimal flux noise of 2.5×10^{-5}Φ_0/\sqrt{Hz} and a magnetic field sensitivity of 38fT/\sqrt{Hz} in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm^2 substrate is 1.35mm^2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HT_c rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges.     

提高激光抽运铯原子磁力仪灵敏度的研究

本文报道了一种基于激光抽运射频共振的铯原子磁力仪. 通过圆偏振光将铯原子抽运到暗态, 实现偏极化. 外磁场存在时, 原子磁矩将以拉莫尔频率绕外磁场进动. 在共振射频磁场的作用下, 原子被去极化而重新吸收光子. 通过探测出射光光谱可以测得拉莫尔频率进而得到外磁场的信息. 本文通过运用自制的894 nm 外腔半导体激光器, 建立了激光稳频装置和低噪声磁场测量环境, 实现了一种基于铯原子激光抽运射频共振的磁力仪. 通过磁力仪参数优化以及闭环测量, 磁力仪测量的外磁场达到了19 fT/Hz^1/2的极限灵敏度和1.8 pT/Hz^1/2的本征灵敏度, 空间分辨率小于2 cm. 关键词： 光抽运 塞曼效应 光探测磁共振 磁力仪     

多孔性氟化物助熔剂制备Eu2+:(Sr,Ca) AlSiN3红色荧光粉

H-PAF （Micro-porous aluminum fluoride）是一种比表面积为20~200 m²/g的多孔性氟化物,具有熔点低、活性高等特性。在Eu²⁺：（Sr,Ca） AlSiN₃烧成工艺中作为助熔剂使用,与传统的氟化物、硼酸等助熔剂相比,可以有效增加Eu²⁺：（Sr,Ca） AlSiN₃荧光粉在合成过程中总的反应活性,降低反应温度50℃以上,并改善荧光粉的发光性能。本文以H-PAF多孔性氟化物为助熔剂,合成了Eu²⁺：（Sr,Ca） AlSiN₃荧光粉,合成温度从1 800℃降低到1 750℃,而且XRD衍射峰更尖锐,说明H-PAF的添加使晶体结晶性更好。测试了Eu²⁺：（Sr,Ca） AlSiN₃荧光粉搭配Ga-YAG绿色荧光粉制成器件后的光效。发现添加PAF后,Eu²⁺：（Sr,Ca） AlSiN₃荧光粉用粉量降低约5%,器件光通量提高2%以上。     

Superconducting phase qubits with shadow-evaporated Josephson junctions

We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device(SQUID) detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm~2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems(TLS) residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T_1 and dephasing time T_φ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.     

采用超导量子干涉组件在微特斯拉磁场下获取超极化~3He的核磁共振波谱和影像(英文)

该文以超导量子干涉元件研究光激发氦三极化气体的低磁场磁共振与造影术.使用圆偏极化雷色光将氦三气体极化,超导量子干涉元件磁共振与造影之测量是以磁通耦合方式来进行,超导量子干涉元件是用铋锶钙铜氧高溫超导罐来隔离环境噪音.此方法测得的磁共振信号与影像相较于直接将样品置于杜瓦瓶下方有较高的信噪比,当样品无法靠近感测元件时,此装置具高信噪比特色.磁通耦合方式的超导量子干涉元件低磁场磁共振与造影术及其氦三极化气体的肺部造影在学术与应用上是相当有趣.     

High-sensitive phototransistor based on vertical HfSe2/MoS2 heterostructure with broad-spectral response

Van der Waals heterostructures based on the two-dimensional (2D) semiconductor materials have attracted increasing attention due to their attractive properties. In this work, we demonstrate a high-sensitive back-gated phototransistor based on the vertical HfSe₂/MoS₂ heterostructure with a broad-spectral response from near-ultraviolet to near-infrared and an efficient gate tunability for photoresponse. Under bias, the phototransistor exhibits high responsivity of up to 1.42×10³ A/W, and ultrahigh specific detectivity of up to 1.39×10¹⁵ cm·Hz^1/2·W^-1. Moreover, it can also operate under zero bias with remarkable responsivity of 10.2 A/W, relatively high specific detectivity of 1.43×10¹⁴ cm·Hz^1/2·W^-1, ultralow dark current of 1.22 fA, and high on/off ratio of above 10⁵. These results should be attributed to the fact that the vertical HfSe₂/MoS₂ heterostructure not only improves the broadband photoresponse of the phototransistor but also greatly enhances its sensitivity. Therefore, the heterostructure provides a promising candidate for next generation high performance phototransistors.     

极低温散粒噪声测试系统及隧道结噪声测量

介观体系输运过程中载流子的离散性导致了散粒噪声.通过测量散粒噪声可以得到传统的基于时间平均值的电导测量无法得到的随时间涨落信息,因而作为一种重要手段在极低温量子输运研究中得到了一定的应用.极低温环境下的噪声测量是一种难度很大的极端条件下的微弱信号测量,通常需要在低温端安装前置放大器并且尽量靠近待测器件以提高测量信噪比和带宽,因此对放大器的噪声水平和功耗都有严格的要求.提出了在稀释制冷机内搭建的散粒噪声测量系统,以及利用此套系统得到了在mK温区超导隧道结散粒噪声的测量结果.自行研制的高电子迁移率晶体管低温前置放大器采用整体封装,便于安装在商用干式稀释制冷机的4 K温区,本底电压噪声为0.25 nV/√Hz,功耗仅为0.754 mW.通过对隧道结进行散粒噪声测量,得到的Fano因子和理论计算吻合.     

Tuning an rf-SQUID flux qubit system＇s potential with magnetic flux bias

At an extremely low temperature of 20 mK, we measured the loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop (Φ f ) and the small dc-SQUID (Φ cjj f ), respectively, the potential shape of the system can be fully controlled in situ. Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed, from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.