Quantum Phase Slip Nanowires for Current Standards

当前标准的量子相滑纳米线

• 批准号: EP/G061939/1
• 负责人: Paul Warburton
• 金额: $ 48.76万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FG061939%2F1
• 关键词: Quantum; Phase; Slip; Nanowires; Current

The Volt is currently defined with accuracy of one part in ten-thousand trillion using the Josephson junction. The Ohm is currently defined with accuracy of one part in ten billion using the quantum Hall effect. The weakest link in the metrological triangle of electrical S. I. units is the Ampre. This is currently defined by means of Coulomb blockade effects in a single-electron pump. The accuracy here however is worse than one part in a hundred million, i.e. more than eight orders of magnitude worse than the Josephson voltage standard. The aim of this proposal is to conduct feasibility studies on the use of quantum phase-slip (QPS) nanowires as a fundamental current standard with accuracy potentially exceeding one part in a hundred million.The quantum phase-slip (QPS) nanowire was proposed by Mooij and colleagues initially for experiments in quantum computation. It was subsequently shown that a voltage-biased QPS nanowire is the precise dual of the current-biased Josephson junction. The Josephson voltage standard is based upon measurement of Shapiro steps - i.e. steps at constant voltage in the current-voltage characteristics when the microwaves at (typically) 70 GHz are coupled to the junction. Making appropriate transformations one would expect that steps at constant current would appear in the current-voltage characteristics of a QPS nanowire when microwaves are coupled to it. If the microwave frequency is f then the steps appear at equally-spaced currents i = 2nef, where e is the electronic charge and n an integer. Hence the current-frequency relationship depends only upon the quantum number e, and measurements anywhere in this universe should therefore yield a current standard which is ultimately limited only by the accuracy of the measurement of the microwave frequency.The above discussion necessarily pre-supposes the existence of quantum phase slips in superconducting nanowires. While their existence seems plausible, as yet there has been no compelling experimental evidence for this. Most of the published experiments on superconducting nanowires to date focus on the measurement of a resistance below the bulk transition temperature of the superconductor, this resistance being larger than that predicted by the standard LAMH model of thermally-activated phase slips. The interpretation of these data has however been called into question by Rogachev et al. who showed that this enhanced resistance could also be accounted for by thermal activation simply by using a modified LAMH model. Since resistance measurements alone are open to this ambiguity of interpretation, in our experiments we will attempt to experimentally address the fundamental physics question at the heart of the QPS nanowire: Is there a sinusoidal voltage-charge relationship? (This is the dual of the first Josephson equation which states that there is a sinusoidal current-phase relationship in a Josephson junction.) We will do this by a series of experiments on QPS devices of increasing complexity, culminating at the end of the three-year programme in attempts to measure microwave-induced constant-current steps in QPS nanowires.

目前，伏特的定义精度为一万万亿分之一，使用约瑟夫森结。欧姆目前定义的精度为一百亿分之一使用量子霍尔效应。电S的三角形中最薄弱的环节。I.单位是安培。目前，这是通过单电子泵中的库仑阻塞效应来定义的。然而，这里的精度比一亿分之一差，即比约瑟夫森电压标准差八个数量级以上。这项提案的目的是对使用量子相位滑移（QPS）纳米线作为基本电流标准进行可行性研究，其精度可能超过一亿分之一。量子相位滑移（QPS）纳米线最初由Mooij及其同事提出，用于量子计算实验。随后证明了电压偏置的QPS纳米线是电流偏置的约瑟夫森结的精确对偶。约瑟夫森电压标准基于Shapiro阶跃的测量，即当（通常）70 GHz的微波耦合到结时，电流-电压特性中的恒定电压阶跃。进行适当的变换，人们可以预期，当微波耦合到QPS纳米线时，在恒定电流下的台阶将出现在QPS纳米线的电流-电压特性中。如果微波频率为f，则台阶出现在等间距电流i = 2nef处，其中e是电子电荷，n是整数。因此，电流-频率关系只取决于量子数e，因此在宇宙中任何地方的测量都应该产生一个电流标准，它最终只受微波频率测量精度的限制。上述讨论必然以超导纳米线中存在量子相位滑移为前提。虽然它们的存在似乎是可信的，但迄今为止还没有令人信服的实验证据。迄今为止，大多数关于超导纳米线的公开实验都集中在测量超导体的体转变温度以下的电阻，该电阻大于由热激活相滑移的标准LAMH模型预测的电阻。然而，Rogachev等人对这些数据的解释提出了质疑，他们表明，这种增强的电阻也可以简单地通过使用修改的LAMH模型通过热活化来解释。由于单独的电阻测量是开放的这种模糊的解释，在我们的实验中，我们将尝试解决QPS纳米线的核心的基本物理问题：是否有一个正弦电压-电荷关系？(This是第一个约瑟夫森方程的对偶方程，该方程指出约瑟夫森结中存在正弦电流-相位关系。）我们将通过对QPS设备进行一系列复杂性不断增加的实验来做到这一点，最终在为期三年的计划结束时尝试测量微波诱导的QPS纳米线恒流步骤。

项目成果

Compact chromium oxide thin film resistors for use in nanoscale quantum circuits

• DOI: 10.1063/1.4901933
• 发表时间: 2014-07
• 期刊: Journal of Applied Physics
• 影响因子: 3.2
• 作者: C. Nash;J. C. Fenton;N. G. N. Constantino-N.-G.-N.-Constantino-50812806;P. Warburton

Embedding NbN Nanowires Into Quantum Circuits With a Neon Focused Ion Beam

• DOI: 10.1109/tasc.2016.2525988
• 发表时间: 2016-04-01
• 期刊: IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY
• 影响因子: 1.8
• 作者: Burnett, J.;Sagar, J.;Fenton, J. C.
• 通讯作者: Fenton, J. C.

Superconductivity of freestanding tungsten nanofeatures grown by focused-ion-beam.

• DOI: 10.1166/jnn.2010.2850
• 发表时间: 2010-11
• 期刊: Journal of nanoscience and nanotechnology
• 作者: Wuxia Li;C. Gu;P. Warburton

The radio-frequency impedance of individual intrinsic Josephson junctions

各个固有约瑟夫森结的射频阻抗

• DOI: 10.1063/1.3275741
• 发表时间: 2009
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Leiner J

Atomic resolution top-down nanofabrication with low-current focused-ion-beam thinning

采用低电流聚焦离子束减薄的原子分辨率自上而下纳米加工

• DOI: 10.1016/j.mee.2012.07.108
• 发表时间: 2012-10
• 期刊: Microelectronic Engineering
• 影响因子: 2.3
• 作者: Wuxia Li