Using graphene multilayers to transform the performance and functionality of atom chips for use in quantum sensors

Crawford, Rosemary (2019) Using graphene multilayers to transform the performance and functionality of atom chips for use in quantum sensors. PhD thesis, University of Nottingham.

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Current atom chips, conventionally made from metal wires, suffer from anumber of different problems, which we have shown can be overcome byusing graphene conductors, specifically;

•Metal wires have a large Johnson noise due to the high carrier density.Graphene has a much lower charge carrier density(≈8 orders of magnitude lower), and thus, Johnson noise that is four orders of magnitude lower than metal. This leads to a corresponding major increase in the lifetime of the atom cloud above the wire. We have shown that an atom cloud trapped 1μm above a graphene wire has its lifetime increased by around 4 orders of magnitude compared to metal, i.e from 0.1 s to>10 minutes. This extends the Johnson noise limited lifetime so much that it becomes negligible as it is far beyond the limit imposed by the background gas collisions.

•Metal wires exert a large Casimir-Polder attraction on atoms trapped near them, thereby limiting the minimum trapping distance to 10-100μm. Using a transfer matrix method in conjunction with the Lifshitz approach, we have demonstrated that the Casimir-Polder attraction between a graphene layer and an atom is approximately 50% that of the attraction between an atom and a thin gold layer. This enables atoms to be trapped up to 2 orders of magnitude closer to a graphene atom chip and so achieve sub-micron trapping distances.

•Metal wires are spatially imperfect on 200 nm scales [1], which can lead to fragmented atom clouds. We have that shown that current lithography techniques can produce conducting paths of an arbitrary shape in graphene with roughness on only the≈10 nm scale. This leads to smoother traps and therefore smoother clouds even at sub-micron trapping distances.

•Finally, we note that graphene will also allow for a greater degree of integration between all the different components of the cold atom system, trapping wires, Ultra High Vacuum (UHV) environments and optics,thus aiding the miniaturisation of the experimental set-up.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Fromhold, T.M.
Keywords: Graphene conductors; Casimir-Polder attraction; Atom clouds
Subjects: Q Science > QC Physics > QC501 Electricity and magnetism
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 57010
Depositing User: Crawford, Rosemary
Date Deposited: 30 Mar 2020 08:36
Last Modified: 06 May 2020 09:18

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