Josephson Parametric Amplifiers using CVD graphene junctions

使用 CVD 石墨烯结的约瑟夫森参量放大器

• 批准号: EP/Y003152/1
• 负责人: Michael Thompson
• 金额: $ 12.71万
• 依托单位: Lancaster University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FY003152%2F1
• 关键词: Josephson; Parametric; Amplifiers; using; CVD

This collaborative project brings together the capabilities of international collaborators who are experts in fabricating superconducting junctions devices using graphene, with UK based expertise in performing low-noise electronic measurements at ultra-low temperatures to develop superconducting amplifiers that will improve the performance of superconducting quantum circuits. Quantum systems are generally very sensitive to noise. In quantum computing, for example, qubits are characterised by coherence, a property which describes how long a qubit can remain in a given quantum state. Noise causes decoherence which limits the lifetime of these delicate systems. One source of noise is the amplifiers that we use to amplify the very low power signals used to control these quantum systems. In superconducting circuits we can use parametric amplifiers that employ Josephson junctions to create amplifiers that can operate at the very lowest possible noise levels, limited only by quantum mechanics. Most commonly, these amplifiers use Josephson junctions that are formed by connecting two superconductors with an insulator, a so-called SIS junction. The operating frequency of parametric amplifiers employing SIS junctions can be tuned using magnetic flux, however due to the long range effects of magnetic fields, this magnetic flux can interfere with our delicate quantum devices, or create cross-talk between multiple amplifiers. Screening this flux therefore creates additional challenges. Superconducting junctions can also be formed by connecting two superconductors with graphene, an SgS junctions. Unlike parametric amplifiers using SIS junctions, parametric amplifiers using SgS junctions can instead be tuned electrostatically. This is achieved by applying a voltage to a gate electrode near the graphene. In this way, we can avoid the perils of the interference caused by stray magnetic flux. However, the development of SgS junctions is overwhelmingly focused on using graphene that is exfoliated from high quality graphite crystals. Although this produces the highest quality graphene, the flakes are only a few micrometers in size, which limits the number of junctions that can be fabricated from a single flake. This makes a practical realisation of devices using these junctions very challenging. Graphene can also be produced in large areas, enough to cover a 6-inch diameter silicon wafer and can be readily purchased. This form of graphene is generally of a lower quality, however Junctions using large-area graphene have been demonstrated. Unfortunately, there has been almost no development of devices which exploit these junctions. This project seeks to develop a robust method for fabricating superconducting junctions and then to develop parametric amplifiers using the junctions. Through this proof-of-concept work we aim to demonstrate that scalable, electrostatically tuned parametric amplifiers is a possibility. These amplifiers could be used for the readout of superconducting qubits and by operating with very low noise, could help in reducing decoherence of these systems. As they are less sensitive to magnetic fields, these amplifiers would also be more robust against such interference. More widely, superconducting microwave amplifiers are used in experiments searching for Axions, a dark matter candidate and can also be used for radio astronomy. The low heat capacity of graphene will also allow the fabrication of very sensitive bolometers with low noise parametric amplifiers. Success in this project would bring the expertise of a world leading research group to the UK and deliver a key enabling technology that would strengthen the UK's position as a world leader in quantum technologies.

该合作项目汇集了国际合作者的能力，他们是使用石墨烯制造超导结器件的专家，并拥有英国在超低温下进行低噪声电子测量的专业知识，以开发超导放大器，从而提高超导量子电路的性能。量子系统通常对噪声非常敏感。例如，在量子计算中，量子位的特征是相干性，这是一种描述量子位在给定量子状态下可以保持多长时间的属性。噪声会导致退相干，从而限制了这些精密系统的使用寿命。噪声源之一是我们用来放大用于控制这些量子系统的极低功率信号的放大器。在超导电路中，我们可以使用采用约瑟夫森结的参量放大器来创建可以在尽可能低的噪声水平下运行的放大器，仅受量子力学的限制。最常见的是，这些放大器使用约瑟夫森结，该结是通过将两个超导体与绝缘体连接而形成的，即所谓的 SIS 结。采用 SIS 结的参量放大器的工作频率可以使用磁通量进行调节，但是由于磁场的长距离影响，这种磁通量可能会干扰我们精密的量子设备，或者在多个放大器之间产生串扰。因此，筛选这种通量会带来额外的挑战。超导结也可以通过用石墨烯连接两个超导体来形成，即SgS结。与使用 SIS 结的参量放大器不同，使用 SgS 结的参量放大器可以进行静电调谐。这是通过向石墨烯附近的栅电极施加电压来实现的。这样就可以避免杂散磁通干扰的危险。然而，SgS 结的开发主要集中在使用从高质量石墨晶体上剥离的石墨烯。尽管这样可以生产出最高质量的石墨烯，但石墨烯薄片的尺寸只有几微米，这限制了单个石墨烯薄片可以制造的结的数量。这使得使用这些结点的设备的实际实现非常具有挑战性。石墨烯还可以大面积生产，足以覆盖直径6英寸的硅晶圆，而且很容易购买。这种形式的石墨烯通常质量较低，但是已经证明了使用大面积石墨烯的结。不幸的是，几乎没有开发出利用这些连接点的设备。该项目旨在开发一种稳健的方法来制造超导结，然后使用该结开发参数放大器。通过这项概念验证工作，我们旨在证明可扩展的静电调谐参量放大器是可能的。这些放大器可用于读取超导量子位，并且通过以非常低的噪声运行，有助于减少这些系统的退相干。由于它们对磁场不太敏感，因此这些放大器对此类干扰的抵抗力也更强。更广泛的是，超导微波放大器用于寻找轴子（暗物质候选者）的实验，也可用于射电天文学。石墨烯的低热容量还允许制造具有低噪声参数放大器的非常灵敏的辐射热测量计。该项目的成功将为英国带来世界领先研究小组的专业知识，并提供关键的支持技术，从而巩固英国作为量子技术世界领导者的地位。