Since the seminal work by Loss and DiVincenzo, quantum dots (QDs) have been extensively studied as building blocks for quantum information processing (QIP). Presently, the most advanced implementations of QD qubits are realised in III/V heterostructures (GaAs/AlGaAs). However, the strong spin-orbit and hyperfine interactions in these compounds pose fundamental limits to the spin coherence time, and so stimulating the search for alternative host materials.Graphene, a two-dimensional single atomic layer of carbon atoms, was successfully produced for the first time in 2004. Despite its short history, its unique material properties have ensured a rapid growth of interest in several areas of science and technology. Spin-orbit coupling and hyperfine interaction with carbon nuclei are both small in graphene, and a very long spin relaxation length has been demonstrated, which make graphene a promising candidate for quantum information technology and spin qubit embodiment.Superior transport properties of graphene encourage the downscaling of graphene devices to the regime where coherent nature of electronic and spin states can be fully exploited. This requires the development of ultrafine patterning technologies which enables accurate nanoscale fabrication beyond the present electron-beam lithography technique. Therefore, inspired by the on-going trend towards device miniaturization, we present a novel hybrid fabrication method for graphene nano devices (e.g. graphene QDs devices) with minimum feature sizes of ~3 nm (i.e. the gap between the graphene side-gates and channel). Here, for the first time we combine conventional e-beam lithography and direct milling with the sub-nm focused helium ion beam generated by a helium ion microscope to fabricate high resolution graphene QDs devices, reliably and reproducibly. The highly controllable, fine scale fabrication capabilities offered by this approach could lead to a more detailed understanding of the electrical characteristics of graphene quantum devices and pave the way towards room-temperature operable grapheme quantum dot devices.
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