1V脉冲驱动型交流量子电压源研究

脉冲驱动型交流量子电压标准ACJVS通过高速脉冲序列驱动约瑟夫森结阵芯片的方式实现宽频带交流量子电压的合成,相比于可编程型交流量子电压标准PJVS,具有免台阶切换、频谱纯净、频带宽等优点。搭建的系统主要包括8位高速脉冲码型发生器、微波放大器、直流阻断、约瑟夫森结阵芯片等。通过驱动包含4个子阵列,每个子阵列含12810个约瑟夫森结的结阵芯片,并结合4通道联合低频补偿的方式,成功产生了1V有效值的脉冲驱动型交流量子电压,为进一步建立交流量子电压基准打下了坚实的基础。最后,展望了脉冲驱动型交流量子电压在量子阻抗桥、交流量子功率源、交流量子功率表方面的应用价值。     

交流约瑟夫森电压合成装置的研究

设计制作了一套交流约瑟夫森电压合成装置(JAWS),能够驱动1 V SINIS型可编程约瑟夫森结阵合成峰值1.2 V、 200 Hz以下频率的交流量子电压。实验结果表明,该装置能够合成200 Hz以下频率的交流量子电压,且合成60 Hz交流电压的不确定度优于5×10^-6,为进一步开展我国首个交流量子电压基准的研究工作奠定了基础。     

可编程约瑟夫森结阵偏置组合算法研究

在可编程约瑟夫森量子电压标准系统中，快速并准确地计算各约瑟夫森子结阵的偏置状态是实现量子电压精准输出的前提。传统的枚举-索引算法通过遍历所有可能的偏置组合以寻找最优解，因此计算效率较低，难以适应量子电压非周期性连续变换输出等特殊应用场景。基于此，提出了一种面向三进制可编程约瑟夫森结阵的偏置组合算法。首先根据各子结阵中包含的约瑟夫森单结数量特征对子结阵进行自适应分组，并据此快速计算预偏置组合；进一步地，结合近似计算方法和量化误差补偿方法，克服预偏置组合中可能存在的子结阵失效、亚分辨率设计等特殊问题。实验结果表明，该算法在多种条件下均能找到最优偏置组合，并且计算效率明显优于传统的枚举-索引算法。     

10V约瑟夫森结阵电压基准

在 1V约瑟夫森结阵电压基准的基础上 ,10 V约瑟夫森结阵电压基准于 1999年底在中国计量科学研究院量子部电压实验室建立。其校准电压在 0 .1V～ 10 V范围内连续可调。校准固态电压标准 10 V输出值的合成不确定度为 5.4× 10 -9(1σ)     

双通道约瑟夫森结阵测试系统的设计

针对目前逐渐增多的芯片测试需求,设计了双通道约瑟夫森结阵测试系统,包括低温测试探杆、微波传输结构等关键部分。测试系统可实现对两个可编程约瑟夫森结阵器件进行同时测量,还可以实现两个芯片的叠加电压输出,通过对一个双通道可编程器件的测量验证了测试系统的上述功能。所测器件的最佳工作频率为17GHz,在未加功率放大器的情况下工作功率为11 dBm。双通道小电压可编程约瑟夫森结阵器件最小结阵为1个结,输出电压为35.15μV;最大结阵为512个结,输出电压为17 998.42μV,量子电压台阶的展宽范围为2μV,这是由于34 420A(1 V档)噪声和测试系统噪声导致,满足量子电压测试需求。双通道的量子电压单结叠加输出为70.30μV,512个结叠加输出为35 996.84μV,叠加后量子电压台阶的展宽范围也在2μV以内,证明双通道约瑟夫森结阵测试系统不仅能对两个独立可编程芯片进行测量,还能够实现量子电压叠加输出功能,在不增加工艺难度的前提下,实现了更大量子电压的输出。     

基于约瑟夫森量子电压的谐波电压测量方法研究

约瑟夫森量子电压目前大多应用于正弦信号的测量,极少有针对谐波信号的研究。对可编程约瑟夫森电压基准应用于谐波检测的可行性进行了研究,实现谐波电压向量子电压过渡。在使用阶梯波交流量子电压进行谐波电压测量时,由于过渡过程和吉布斯现象的存在,部分数据出现较大波动;若将该部分处于过渡过程的数据纳入傅里叶变换,会导致恢复得到的信号幅值和相位失真。针对这一问题,提出了一种新的谐波电压计算方法:加权傅里叶变换。该方法通过将处于过渡过程的数据权重置零的方式,实现了谐波电压的准确测量。实验结果表明,谐波电压幅值和相位测量结果较理想,幅值测量标准差均小于1 μV,相位测量标准差均小于15 μrad。     

免液氦量子电压标准低温系统设计与研究

提出一种免液氦量子电压标准低温系统，给出了设计和结构，详细分析了10 K左右NMIJ结阵的结构和超导特性。实验结果表明，设计和研制的免液氦量子电压标准低温系统，能够较好地为NMIJ约瑟夫森结阵提供10 K左右低温环境，测得的临界电流和超导量子电压台阶宽度满足结阵超导特性使用要求，为下一步直流量子电压的准确输出奠定了基础。     

10伏约瑟夫森结阵电压基准获国家科技进步奖

我院研制的“10伏约瑟夫森结阵电压基准”装置,荣获2 0 0 3年度国家科技进步奖二等奖。10伏约瑟夫森结阵电压基准是量子基准。1990年1月1日,国际计量委员会推荐用约瑟夫森效应复现电压单位量值,以保证国际范围内溯源的一致性。美、德、法、日等发达国家相继建立了1伏及10伏的约瑟夫森电压基准。我院1994年研制出1伏约瑟夫森结阵电压基准,1996年由世行贷款立项,建立10伏约瑟夫森结阵电压基准课题,于1999年研制成功,该装置系统的测量不确定度为5 4×10 - 9,达到了国际先进水平。10伏约瑟夫森结阵电压基准利用低温超导结电子跃迁效应复现电压…     

交流量子电压标准研究综述

相比于传统的实物电压标准,基于约瑟夫森效应建立的交流量子电压标准,具有复现性好、稳定性高和不确定度低等优点。从物理原理、存在问题以及应用价值等角度出发,梳理、归纳先后发展起来的可编程约瑟夫森电压标准和脉冲驱动的交流约瑟夫森电压标准,并比较这两种量子电压标准的计量性能,介绍我国构建交流量子电压标准的现状及进展。     

基于约瑟夫森量子电压的交流功率测量系统及方法研究

基于约瑟夫森量子电压标准设计了交流功率差分测量系统。通过分析差分采样系统的误差分布及误差传递函数,提出换向差分测量方法,减小了差分采样系统的增益误差,提高了电压幅值测量准确度;通过分析衰减系数η,证明了采用换向差分测量较容易实现10-7量级电压幅值测量。通过评估差分采样系统零相位,结果证明了差分采样系统具有较好的相位测量稳定性。分析了交流功率差分测量系统的不确定度分量,评估了功率因数为1.0,0.5 L和0.5 C时的功率测量不确定度,通过与国家交流功率基准装置进行实验比对,证明了基于约瑟夫森量子电压交流功率测量系统不确定度评估的合理性。     

Theory of the AC Josephson effect in triplet superconducting junction

The quasiparticle and AC Josephson current in superconductor / insulator / superconductor (S/I/S) junctions including a triplet p-wave superconductor are calculated for arbitrary transmission of the junction. As a triplet pairing state we select one of the unitary pairing states which is a promising candidate for the superconducting state in Sr ₂ RuO ₄ . In p-wave superconductor / insulator /p-wave superconductor junction, both quasiparticle current and AC Josephson current are enhanced near zero-bias voltage due to the existence of zero energy state of p-wave superconductors. For the s-wave superconductor/ insulator / p-wave superconductor junction, the quasiparticle current at low voltage is suppressed due to the energy gap of s-wave superconductor. The first Fourier component of the AC Josephson current vanishes due to the difference of the parity between the two superconductors.     

约瑟夫森结Nb电极的实验研究

通过溅射Nb膜张力与氩（Ar）压强的关系，超导转变温度Tc，室温阻扰与液氮温度阻抗比RRT／RLN2，沉积中Ar浓度CAr与负偏压关系的测量和扫描电子显微镜的观察分析，对约瑟夫森结Nb电极作了研究。发现Ar压强在1．1Pa时，Nb膜呈现无应力状态；低负偏压下沉积的Nb膜晶粒结构是由致密膜到圆柱状。在偏压Ub＝－50V时，获得表面致密均匀、晶粒结构合适的Nb膜。对Nb膜用阳极氧化电压谱图（AVS）分析，证实沉积的Nb膜内不存在氧化物、寄生结和分层界面。     

Operation of NIST Josephson Array Voltage Standards

This paper begins with a brief discussion of the physical principles and history of Josephson effect voltage standards. The main body of the paper deals with the practical details of the array design, cryoprobe construction, bias source requirements, adjustment of the system for optimum performance, calibration algorithms, and an assessment of error sources for the NIST-developed Josephson array standard.     

Quasiparticles and Polaronic Effects in Crystals,Fermi Gasses and Fermi Liquids

We study the effect of quantum and classical phase fluctuations on the phase transitions in the system of Josephson-junction arrays. We employed a variational method for calculating the Gaussian type fluctuation of the phase in the Josephson-junction array lattice systems without and with an external magnetic field. We investigate the spectrum of collective excitations and the effects of collective excitations on the transport properties of Josephson-junction arrays. We showed that the Hamiltonian for the lattice system of the Josephson junction is the same as the Hamiltonian for the classical or quantum two-dimensional interacting rotators. We also showed that the dynamics of fluctuations of the phase in the lattice system of Josephson junction is very similar to the lattice dynamics of the lattice in crystals. We also showed that in the lattice system of Josephson junctions there is the collective acoustic mode similar to the acoustic mode in the crystal lattice, and this mode may lead to the dissipation of the Josephson current in the superconducting array of Josephson junctions. The speed of sound of the collective acoustic mode of the phase fluctuation depends on the Josephson coupling energy and the Coulomb charging energy. The contribution of the collective acoustic mode to the low temperature specific heat is the same as the contribution of the acoustic phonons to the specific heat of crystals. We also discuss the future development of results and their application.     

Phase Transitions and Phase Fluctuations in the Josephson-Junction Arrays

We study the effect of quantum and classical phase fluctuations on the phase transitions in the system of Josephson-junction arrays. We employed a variational method for calculating the Gaussian type fluctuation of the phase in the Josephson-junction array lattice systems without and with an external magnetic field. We investigate the spectrum of collective excitations and the effects of collective excitations on the transport properties of Josephson-junction arrays. We showed that the Hamiltonian for the lattice system of the Josephson junction is the same as the Hamiltonian for the classical or quantum two-dimensional interacting rotators. We also showed that the dynamics of fluctuations of the phase in the lattice system of Josephson junction is very similar to the lattice dynamics of the lattice in crystals. We also showed that in the lattice system of Josephson junctions there is the collective acoustic mode similar to the acoustic mode in the crystal lattice, and this mode may lead to the dissipation of the Josephson current in the superconducting array of Josephson junctions. The speed of sound of the collective acoustic mode of the phase fluctuation depends on the Josephson coupling energy and the Coulomb charging energy. The contribution of the collective acoustic mode to the low temperature specific heat is the same as the contribution of the acoustic phonons to the specific heat of crystals. We also discuss the future development of results and their application.