Quantum Metrological Triangle

Centre for Metrology and Accreditation (MIKES)

TKK Low Temperature LaboratoryVTT Quantronics group

Antti ManninenMIKES9.11.2006

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?

Josephson

effect

Single charge pumping

Qua

ntum

Hal

l effec

t

I = n

1(e

2 /h)U U

= n

2 (h/2e)f

I = n3ef

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

Principle of experiment

QHR(quantum Hall resistance)

CPP(Cooper pair pump)

J V (J osephson voltage standard)

BOT/SQUID

(zerodetector)

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

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)

J osephsonjunction(s)

S/Njunction

Al

Al

CuCr

COLLECTOR BASE

EMITTER

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))

Vg

I

-Ne

-Ne

T = 1/f

6

m

Tunnel junctions of SQUID 2

Gate

Mesoscopic island

-N·2e

-N·2e

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

How to decrease leakage current? (MIKES-CoE collaboration)

First idea: several SQUIDs in series

MAGNETICFLUX

GATEVOLTAGE

MAGNETICFLUX

SQUIDSQUID

QUANTIZED CURRENT

SUPERCONDUCTINGISLAND

SQUID

SQUID

SQUID

SQUID

SQUID

SQUID

How to decrease leakage current? (MIKES-CoE collaboration)

First idea: several SQUIDs in series

MAGNETICFLUX

GATEVOLTAGE

MAGNETICFLUX

SQUIDSQUID

QUANTIZED CURRENT

SUPERCONDUCTINGISLAND

SQUID

SQUID

SQUID

SQUID

SQUID

SQUID

How to decrease leakage current? (MIKES-CoE collaboration)

First idea: several SQUIDs in series

Second idea: 3-junction SQUIDs

· In progress

MAGNETICFLUX

GATEVOLTAGE

MAGNETICFLUX

SQUIDSQUID

QUANTIZED CURRENT

SUPERCONDUCTINGISLAND

SQUID

SQUID

SQUID

SQUID

SQUID

SQUID

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?

MAGNETICFLUX

GATEVOLTAGE

MAGNETICFLUX

SQUIDSQUID

QUANTIZED CURRENT

SUPERCONDUCTINGISLAND

SQUID

SQUID

SQUID

SQUID

SQUID

SQUID

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