Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Miniature SQUID device that is quantum limited and can detect a few electronic spins in unit bandwidth

Concerning the development of SQUIDs as potential Mn12 based Qbit detectors, NPL has tested many and developed several devices. Devices were obtained from commercial fabrication facilities, HYPRES in US, from world leading research groups, s Wernsdorfer in Grenoble and Lam, CSIRO in Australia. Also both Aluminium and Niobium based devices from CSIC-IMM were tested as well. We also sent some of our devices to CSIC-UB for inclusion in their experiments on microwave emission from Mn12 single crystals. Sensitivity of the devices was measured as well as a full characterisation of their I-V curves as functions of temperature and their response to magnetic fields. Using a newly acquired apparatus for this project, an Adiabatic demagnetisation refrigerator, we were able to test devices down to 50mK simulating the operating conditions of the devices if they are to be used as QBit detectors. Using our measurements we were able to give feedback to the fabrication process so that better devices could be made. An example was the recommendation that a Gold overlayer of specific thickness be applied to the Niobium devices from CSIRO and that the geometry of the junction design was changed. This work has enabled us to form relations and synergies with these important groups and so to raise our profile and capability within Europe. These devices have potentially a wide range of applications that can impinge on various aspects of the quality of life, for example as THZ detectors for security screening.

Objectives of the CSIC-IMM unit within the project were initially limited to supply fabrication technology for superconducting devices, such as state-of-the-art micro-SQUIDs and superconducting circuits and switches for magnetic qbit preparation and characterisation. Evolution of the project forced the activity of this unit to focus on extremely small micro-SQUID development, trying to extend the device sensitivity beyond state-of-the-art and to be able to measure single spin clusters with S=10. Interest on this extremely difficult to achieve objective with CSIC-IMM experience and technology faded out as measurement attempts at NPL and contacting difficulties resulted in blown-up or short-circuit devices at low temperatures.

The experience gained through these developments is of great value for our scientific community and society. First, because this project has directly promoted the establishment of the first operative e-beam nanofabrication laboratory in our country and helped training technical personnel in a field previously absent. Second , because this know-how has effectively spread to other two labs in Spain (UAM-CSIC and U Zaragoza) using e-beam lithography at present. Third, because the competitiveness of the fabrication technology at IMM has been enhanced to the point in which, for the first time, it is possible to start competing in high tech projects for the ESA (Superconducting Bolometers for X-Ray Detection and Spectrometry). Synergies with other relevant projects within the group such as IST-NANOMAT and recently SANDIE NoE have been also very positive, as extending the range of applications to the III-V compound nanostructures.

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NPL Management Ltd
National Physical Laboratory
TW11 0LW Teddington
United Kingdom
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