UCL Discovery

## Weak link nanobridges as single flux quantum elements

Shelly, CD; See, P; Ireland, J; Romans, EJ; Williams, JM; (2017) Weak link nanobridges as single flux quantum elements. Superconductor Science and Technology , 30 (9) , Article 095013. 10.1088/1361-6668/aa80cd.

## Abstract

This paper investigates the feasibility of using weak link nanobridges as Josephson junction elements for the purpose of creating Josephson circuits. We demonstrate the development of a single-step electron beam lithography procedure to fabricate niobium nanobridges with dimensions down to $40\,\mathrm{nm}\times 100\,\mathrm{nm}$. The single-step process facilitates fabrication that is scalable to complex circuits that require many junctions. We measure the IV-characteristics (IVC) of the nanobridges between temperatures of $4.2$ and $9\,{\rm{K}}$ and find agreement with numerical simulations and the analytical resistively shunted junction (RSJ) model. Furthermore, we investigate the behaviour of the nanobridges under rf irradiation and observe the characteristic microwave-induced Shapiro steps. Our simulated IVC under rf irradiation using both the RSJ model and circuit simulator JSIM are in agreement with the experimental data. As a potential use of nanobridges in circuits requiring many junctions, we investigate the theoretical performance of a nanobridge-based Josephson comparator circuit using JSIM.

Type: Article Weak link nanobridges as single flux quantum elements An open access version is available from UCL Discovery 10.1088/1361-6668/aa80cd http://doi.org/10.1088/1361-6668/aa80cd English © 2017 IOP Publishing Ltd. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Science & Technology, Physical Sciences, Physics, Applied, Physics, Condensed Matter, Physics, superconductivity, Shapiro steps, nanobridge, Josephson junction, JSIM, VOLTAGE, MICROBRIDGES, TECHNOLOGY UCLUCL > Provost and Vice Provost Offices > UCL BEAMSUCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering ScienceUCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng https://discovery.ucl.ac.uk/id/eprint/10040491