Characterising and Optimising the Microwave Properties of Nanobridge Josephson Junctions

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1. Finite Element ModellingModel the microwave effect on Josephson junctions and SQUIDs with different powers and temperaturesModel the effective inductance of nanoSQUIDs with nanobridge junctions using MDLSI for different loop size and sharpModel the spin detection sensitivity as a function of the position of the spin relative to SQUID1) Position related to SQUIDs loop2) Distance between the SQUIDs loop and spin in z direction2.Fabrication and Experimental SetupFurther development of thin film device fabrication methods, including integration of implanted spin clusters. This involves selection of techniques of junction fabrication, thermal control of chips within cryostat. The devices will be characterised by a range of microscopies (AFM, SEM, etc.)Develop closed cycle cooler system to incorporate SQUID Series Array and integrate readout electronics with the closed-cycle cryostat.Mechanical design and layout using SolidWorks to include Bias T, Circulator, Low Noise Microwave Amplifier and break-out box.3. Series SQUID Array ReadoutNanobridge junction based nanoSQUIDs will be tested and optimised with respect to anumber of parameters including temperature of operation, noise performance and magneticfield operation.Microwave response performance will be measured and compared with the modelling resultsproduced (Chapter 2).Ga FIB and He-Ne FIB device performance will be assessed and optimised (possible paper)Integration of nanoSQUIDs with the SSA readout system will provide a further developmentpath.Noise performance of the nanoSQUID systems will be evaluated, leading to predictions ofspin sensitivity.4.Inductive Microwave ReadoutTo optimise future applications of nanoSQUIDs for quantum technologies it is desirable toincrease the readout bandwidth and sensitivity of the detection system. This will beachieved by implementation of a microwave inductive readout scheme, coupled with apotential manipulation of spins with microwave pulse trains.Integration of cryogenic low-noise amplifier and other microwave components to closedcycle cooler system.Test performance of microwave detection method, in terms of temperature, magnetic fieldand microwave power parameters.5.Spin Cluster DetectionIn order to further develop the system, a range of spin cluster SQUID chips, previouslycharacterised with conventional readout, will be measured with the SSA system.Further optimisation should be possible by integration of the same chips with the microwaveinductive readout system.Operational parameter space (temperature, magnetic field) for both detection schemes