Graphene-based atom chips: a high-performance platform for cold-atom quantum technologies

该项目将开发石墨烯原子芯片，以降低（数量级）原子损失率和原子捕获势的空间尺度，这是便携式芯片量子传感器所需要的。该芯片将使原子玻色-爱因斯坦凝聚体的创建和操作具有比现有设备更低的真空压力要求，从而有助于基于芯片的量子传感器和时钟的可扩展工业制造。原子芯片使用载流微细制造导线来产生磁场，从而控制附近的超冷原子。它们表现出强大的室温操作能力，是基于冷原子的量子传感器/时钟技术的关键组成部分。现有的芯片在大块基板上使用金属导体。电线中的高时空噪声，以及原子对衬底的巨大卡西米尔-波尔德引力，使得原子云迅速破碎和耗尽，除非它们被控制在距离芯片5倍的范围内。这限制了芯片的小型化，限制了芯片产生的潜在景观，并阻止了原子中电子与芯片中电子的相干量子耦合1。该项目旨在通过利用石墨烯和其他二维材料中的二维电子气体中的导体来改变原子芯片的性能。我们最近的工作表明，与金属导体相比，这些结构将使芯片的原子表面分离和功耗分别减少2和5个数量级，并将原子云的寿命增加4个数量级（到分钟）。到目前为止，我们的工作主要集中在石墨烯/氮化硼结构上，这对晶体管和高频电子器件很有希望。在原子芯片中使用类似的结构，为电子和冷原子量子器件的双重应用开辟了可能性。我们现在需要在现有材料（如SiC）的基础上开发石墨烯原子芯片演示品，以展示二维材料作为量子传感器和时钟平台的强大功能。现有的基于sic的石墨烯霍尔棒，用于量子电阻计量，看起来非常适合原理验证研究和随后的优化。该项目将通过以下方式开发基于石墨烯和其他二维材料多层的原子芯片：计算现有石墨烯霍尔棒的原子阱分布和寿命，考虑空间缺陷和Johnson噪声引起的原子损失，使用Green函数模型将噪声特性与多层、隧道和三体过程的电磁反射系数联系起来。对现有的硅基霍尔棒进行了详细的实验分析：它们的电学特性和作为原子芯片陷阱的性能。用随机投影Gross-Pitaevskii模型模拟被困原子云的动力学。设计包含多个2D层的更好的样本以增强功能。由德国合作者对这些改进后的样品进行理论研究。

The project will develop graphene atom chips that reduce (by orders of magnitude) the atom loss rate and spatial scale of the atom trapping potential, as required for portable chip-based quantum sensors. The chips will enable the creation and manipulation of atomic Bose-Einstein condensates with less stringent vacuum pressure requirements than present devices, thus assisting the scalable industry manufacture of chip-based quantum sensors and clocks.Atom chips use current-carrying microfabricated wires to create a magnetic field and thereby control nearby ultracold atoms. They exhibit robust room-temperature operation and are key components of cold-atom-based quantum sensor/clock technologies1. Existing chips use metallic conductors on bulk substrates. High spatio-temporal noise in the wires, and the large Casimir-Polder attraction of atoms to the substrate, makes the atom clouds fragment and deplete rapidly unless they are held within 5 from the chip. This limits miniaturisation of the chips, the potential landscapes that they produce, and prevents coherent quantum coupling of electrons in the atoms to those in the chips1.This project aims to transform atom-chip performance by exploiting conductors within two-dimensional electron gases in graphene and other 2D materials. Our recent work indicates that these structures will reduce the atom-surface separation and power consumption of the chip by 2 and 5 orders of magnitude respectively and increase the atom cloud's lifetime by 4 orders of magnitude - to minutes - compared with metallic conductors.So far, our work has focused on graphene/boron nitride structures, which are promising for transistors and high-frequency electronics2. Using similar structures for atom chips opens the possibility of dual applications in electronic and cold-atom quantum devices. We now need to develop graphene atom-chip demonstrators, based on established materials such as SiC, to demonstrate the power of two-dimensional materials as a platform for quantum sensors and clocks. Existing SiC-based graphene Hall bars3, developed for quantum resistance metrology, look ideal for proof-of-principle studies and subsequent optimisation. The project will develop atom chips based on graphene and other 2D material multilayers by:1. Calculating atom trap profiles and lifetimes for existing graphene Hall bars, taking into account spatial imperfections and atom loss due to Johnson noise, using Green function models to relate the noise characteristics to the electromagnetic reflection coefficients of the multilayers, tunnelling and 3-body processes.2. Undertaking detailed analysis of experiments on existing SiC-based Hall bars: both their electrical properties and performance as an atom chip trap.3. Simulating the dynamics of trapped atom clouds using Stochastic Projected Gross-Pitaevskii models.4. Designing better samples containing multiple 2D layers to enhance functionality.5. Undertaking theoretical studies of experiments to be performed on these improved samples by collaborators in Germany.