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.

这个协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连接设备的专家，并基于英国的专业知识在超低温度下执行低噪声电子测量以开发超导性放大器，从而可以改善超低量子量子通道的性能。量子系统通常对噪声非常敏感。例如，在量子计算中，量子位的特征是连贯性，该属性描述了量子在给定的量子状态中可以保留多长时间。噪声会导致破裂，从而限制了这些细腻系统的寿命。噪声的一种来源是我们用来扩大用于控制这些量子系统的非常低功率信号的放大器。在超导电路中，我们可以使用使用约瑟夫森连接的参数放大器来创建可以在最低可能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连接，这些连接是通过将两个超导体与绝缘体（所谓的SIS连接器）连接起来形成的。可以使用磁通量调整采用SIS连接的参数放大器的工作频率，但是由于磁场的远距离效应，这种磁通量会干扰我们精致的量子设备，或者在多个放大器之间创建互通。因此，筛选此通量会带来其他挑战。超导连接也可以通过将两个超导体与石墨烯（SGS连接）连接起来来形成。与使用SIS连接的参数放大器不同，可以使用SGS连接的参数放大器进行静电调节。这是通过在石墨烯附近的栅极电极上施加电压来实现的。这样，我们可以避免由杂散磁通量引起的干扰的危险。但是，SGS连接的发展主要集中在使用从高质量石墨晶体中去除角质的石墨烯。尽管这会产生最高质量的石墨烯，但薄片的尺寸仅几微米，这限制了可以从单个薄片制造的连接数量。这使得使用这些连接的实际实现非常具有挑战性。石墨烯也可以在大区域生产，足以覆盖直径6英寸的硅晶片，并且可以容易购买。这种形式的石墨烯通常具有较低的质量，但是已经证明了使用大面积石墨烯的结合。不幸的是，几乎没有开发利用这些连接的设备。该项目旨在开发一种可靠的方法来制造超导连接，然后使用交界器开发参数放大器。通过这项概念验证工作，我们旨在证明可扩展的，静电调谐的参数放大器是可能的。这些放大器可用于读取超导QUBITS，并且通过以非常低的噪声操作，可以帮助降低这些系统的破坏。由于它们对磁场不太敏感，因此这些放大器在这种干扰上也将更加健壮。更广泛的是，超导微波放大器用于搜索轴，候选暗物质的实验中，也可以用于射电天文学。石墨烯的低热容量还将允许制造具有低噪声参数放大器的非常敏感的强仪。该项目的成功将使世界领先的研究小组的专业知识进入英国，并提供一项关键的促成技术，从而增强英国作为量子技术的世界领导者的地位。