Quantum Metrological Triangle Centre for Metrology and Accreditation

Quantum Metrological Triangle Centre for Metrology and Accreditation (MIKES) TKK Low Temperature Laboratory VTT Quantronics group

Quantum metrological triangle in short )U e 2/h I= n 1 ( Ha ll ant um Qu e )f ct h/2 effe n 2( son U= eph Jos effe ct • Quantum metrology triangle is one of the greatest challenges of modern metrology. • Is Ohm’s law U = RI valid between the quantum standards of voltage, resistance, and electric current, at uncertainty level of about 10 -7 or better. • Do the fundamental constants e (electron charge) and h (Planck’s constant) have the same value in all three phenomena? Do we I = n 3 ef understand physics well enough? Single charge pumping • Redefinition of kg 2011?

Quantum standards of electricity

Principle of experiment

Biggest challenges

Bloch Oscillating Transistor (BOT) • ”Bipolar transistor” based on single charge effects in a superconductor / normal metal nanostructure • Developed by VTT and TKK/LTL (J. Delahaye, J. Hassel, R. Lindell, M. Sillanpää, M. Paalanen, H. Seppä, and P. Hakonen, Science 299, 1045 (2003). • Especially suitable for measurements at 1 MΩ impedance level (e. g. current pump)

Cooper pair pump (sluice) • Superconducting charge pump with maximum current approaching 1 n. A. • Invented by TKK/LTL and VTT (A. O. Niskanen, J. P. Pekola, and H. Seppä, Phys. Rev. Lett. 91, 177003 (2003)) Mesoscopic island Gate Tunnel junctions of SQUID 2

First pumping experiments (2004) • Proof-of-principle experiment in 2004 by TKK/LTL and VTT (A. O. Niskanen et al. , Phys. Rev. B 71, 012513 (2005)) • On top of the pumped current there is leakage current through the “closed” SQUID, but the difference between “positive” and “negative” pumping directions shows clear step structure with current plateaus at ΔI = N · 2 ef

How to decrease leakage current? (MIKES-Co. E collaboration) First idea: several SQUIDs in series

How to decrease leakage current? (MIKES-Co. E collaboration) First idea: several SQUIDs in series

How to decrease leakage current? (MIKES-Co. E collaboration) First idea: several SQUIDs in series Second idea: 3 -junction SQUIDs · In progress

How to decrease leakage current? (MIKES-Co. E collaboration) First idea: several SQUIDs in series Second idea: 3 -junction SQUIDs · In progress Third idea: something else?

Results with the newest sluice

Financiers of the project • Academy of Finland • TKK and VTT: Centre of Excellence • MIKES: Research project Quantum Metrology Triangle • Technology Industries of Finland Centennial Foundation (starting from January 2007) • Vilho, Yrjö and Kalle Väisälä Foundation • MIKES, TKK, VTT