Browsing by Author "Holmqvist, Tommy"

Now showing 1 - 4 of 4
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    High-resolution superconducting single-flux quantum compator for sub-Kelvin temperatures
    (2006) Savin, Alexander; Pekola, Jukka; Holmqvist, Tommy; Hassel, Juha; Grönberg, L.; Helistö, Panu; Kidiyarova-Shevchenko, A.; Department of Applied Physics
    A design of sub-Kelvin single-flux quantum (SFQ) circuits with reduced power dissipation and additional cooling of shunt resistors has been developed and characterized. The authors demonstrate operation of SFQ comparators with current resolution of 40nA at 2GHz sampling rate. Due to improved cooling the electron temperature in shunt resistors of a SFQ comparator is below 50mK when the bath temperature is about 30mK.
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    Primary tunnel junction thermometry
    (2008-11-14) Pekola, Jukka; Holmqvist, Tommy; Meschke, Matthias; Department of Applied Physics
    We describe the concept and experimental demonstration of primary thermometry based on a four-probe measurement of a single tunnel junction embedded within four arrays of junctions. We show that in this configuration random sample specific and environment-related errors can be avoided. This method relates temperature directly to Boltzmann constant, which will form the basis of the definition of temperature and realization of official temperature scales in the future.
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    Primary Tunnel Junction Thermometry
    (American Physical Society (APS), 2008) Pekola, Jukka P.; Holmqvist, Tommy; Meschke, Matthias; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of Science
    We describe the concept and experimental demonstration of primary thermometry based on a four-probe measurement of a single tunnel junction embedded within four arrays of junctions. We show that in this configuration random sample specific and environment-related errors can be avoided. This method relates temperature directly to Boltzmann constant, which will form the basis of the definition of temperature and realization of official temperature scales in the future.
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    Tunnel junction thermometry and thermalisation of electrons
    (Aalto-yliopiston teknillinen korkeakoulu, 2010) Holmqvist, Tommy; Pekola, Jukka, Prof.; O.V. Lounasmaa -laboratorio; O.V. Lounasmaa Laboratory; Aalto-yliopiston teknillinen korkeakoulu; Kaivola, Matti, Prof.
    In this work, normal metal and superconducting tunnel junctions have been studied. In particular applications in low temperature electronic thermometry are investigated. The double oxidation method for achieving high resistance junctions is described and shown to produce high quality devices. A new invention, the single junction thermometer (SJT), is described, and proof of the concept experiments demonstrating the functionality of the device are described. A key feature of the SJT is a well controlled electromagnetic environment surrounding a single junction. It is shown that embedding a single junction within arrays of other junctions is a superior way for controlling the environment as compared to previously proposed methods. Improved thermalisation of electrons is shown to be beneficial for the performance of superconducting RSFQ (Rapid Single Flux Quantum) devices. The so called grey zone of the most basic of these devices, the balanced comparator, is investigated. Improved performance based on metallic cooling fins has been achieved. In the same spirit improved thermalisation of the Coulomb blockade thermometers extends their operation towards lower temperatures. A method employing thick metallic islands was developed and tested to this end.