Quantum Metrological Triangle

1. Quantum Metrological Triangle Centre for Metrology and Accreditation (MIKES) TKK Low Temperature Laboratory VTT Quantronics group Antti Manninen MIKES 9.11.2006

2. Quantum metrological triangle in short • 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 • understand physics • well enough? • Redefinition of kg 2011? Quantum Hall effect Josephson effect I = n1(e2/h)U U = n2(h/2e)f I = n3ef Single charge pumping

3. Quantum standards of electricity • Voltage and Josephson effect • Using Josephson effect, the unit of voltage can be related to fundamental constants and frequency with relative uncertainty of about 10-10 (U = n(h/2e)f ) • Nobel 1973 (Josephson) • Resistance and quantum Hall effect • Using quantum Hall effect, the unit of resistance can be related to the fundamental constants with relative uncertainty of about 10-9 (RH = (h/e2)/i ) • Nobel 1985 (von Klitzing) and 1998 (Laughlin, Störmer and Tsui) • Electric current and single charge pumping • Using single charge pumping, electric current gan be related to electron charge and frequency (I = kef ) but not yet accurately enough nor at high enough current levels • Not yet Nobel prize

4. Principle of experiment

5. Biggest challenges • Current pump • Cooper pair pump (sluice) invented by TKK/LTL and VTT • A.O. Niskanen et al., Phys. Rev. Lett., 2003 • Zero detector • SQUID or the new Bloch Oscillating Transistor (BOT) invented by VTT and realized by TKK/LTL • J. Delahaye et al., Science, 2003 • Stable cryoresistor • The final experiment as a whole • Comparison of three different quantum standards at relative uncertainty of 10-7 or lower • The new MIKES house

6. 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)

7. Cooper pair pump (sluice) • Superconducting charge pump with maximum current approaching 1 nA. • Invented by TKK/LTL and VTT (A.O. Niskanen, J.P. Pekola, and H. Seppä, Phys. Rev. Lett. 91, 177003 (2003)) Mesoscopic island -N·2e Gate 6 mm -N·2e Tunnel junctions of SQUID 2

8. 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 ·2ef

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

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

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

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

13. Results with the newest sluice

14. 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