Presentation on theme: "Comité Science et métrologie"— Presentation transcript:
1 Comité Science et métrologie Académie des sciencesJean Kovalevsky Christian BordéChristian Amatore Alain AspectFrançois Bacelli Roger BalianAlain Benoit Claude Cohen-TannoudjiJean Dalibard Thibault DamourDaniel Estève Pierre FayetBernard Guinot Theodor HänschSerge Haroche Yves JeanninPierre Perrier Gabriele VenezianoMarc Himbert Ian MillsTerry Quinn Christophe SalomonClaudine Thomas
2 COMITÉ « SCIENCE ET MÉTROLOGIE » DE L’ACADÉMIE DES SCIENCES Effet Hall quantiqueet métrologieColloque organisé par Christian Glattli
3 Quantum Hall effectand the reform of the SIChristian J. Bordé
4 Magnetic Induction B (T) Quantum Hall effectRxyMagnetic Induction B (T)Rxxi=2i=3i=4
5 Metrological triangle Quantum Ohm law SETeffectJosephsoneffectQuantum HalleffectI
6 Watt balance: principle A) Static mode:B) Dynamical mode:MasscomparatorIRadialfieldE.m.f.UUUVelocityInterferometerInterferometerPositionMechanical Power = Electrical Power
8 On electrical units:In the present SI, the values of μ0 and ε0 are fixed andthus the propagation properties of the electromagnetic fieldin the vacuum are also fixed:- propagation velocity- vacuum impedanceelectric and magnetic energy densitiesandgives the radiation pressure andgives the intensity and the number of photonsThis system is perfectly adapted to the propagation of lightin vacuum: no charges but also no ether.
9 Let us now introduce charges. The values of μ0 and ε0 are related to the positron charge eby the fine structure constant:dimensionless constant imposed by nature, extraordinarilywell-known today since its present uncertainty is 0.7x10-9.The free electromagnetic field is coupled to charges throughthis constant, which thus appears as a property of electronsand not as a property of the free electromagnetic field.is just another way to write the positron chargechoice adopted by field-theory experts.
11 Validity of expressions for RK and KJ 3.10-82.10-7
12 On electrical units:It clarifies future issues to introduce a specific notation for theapproximate theoretical expressions of RK and KJ :in order to distinguish them from the true experimental constantsRK and KJ which are related to the previous ones by:Fix h and e would fix the constantsbut not RK and KJ which would keep an uncertainty.This uncertainty is not that related to the determinationof e and h in the SI but to our lack of knowledgeof the correction terms to the expressions of RK and KJ.Let us recall that the present estimate of the value of εKis of the order of and that of εJ of the order ofwith important uncertainties.
13 The fact that the universality of these constants has been demonstrated to a much better level simply suggests thatpossible corrections would involve other combinations offundamental constants: functions of α, mass ratios, …The hydrogen spectrum provides an illustrating exampleof a similar situation. The energy of the levels of atomichydrogen is given to the lowest order by Bohr formula,which can also be derived through a topological argument.Nevertheless there are many corrections to this first terminvolving various fundamental constants.It is not because the spectrum of hydrogen is universal thatwe may ignore these corrections and restrict ourselvesto Bohr formula.
14 HYDROGEN ATOMThe fact that the universality of these constants has been demonstrated to a much better level simply suggests thatpossible corrections would involve other combinations of fundamental constants: functions of α, mass ratios, …The hydrogen spectrum provides an illustrating example of a similar situation. The energy of the levels of atomichydrogen is given to the lowest order by Bohr formula, which can also be derived through a topological argument.Nevertheless there are many corrections to this first term involving various fundamental constants.It is not because the spectrum of hydrogen is universal that we may ignore these corrections and restrict ourselvesto Bohr formula.243 nm
16 Determination of h/mat by Ramsey-Bordé atom interferometry 16uncertainties (x 10-9)Determination of the fine structure constant
17 Validation of the expression of RK from the fine structure constant 10 Janvier 2006Académie des SciencesValidation of the expression of RK from the fine structure constant17
18 Conclusion on electrical units: Even if e is fixed, there remains a largeuncertainty for RK and KJ and in additionvacuum properties acquire an uncertainty.There seems to be no real advantagein fixing the value of e rather than that of μ0.
19 Les effets quantiques de la métrologie électrique Effet JosephsonEffet Hall quantique4 10-9