The Système Internationale d'unités (SI system) is about to undergo its biggest change in half a century by redefining the units for mass and current in terms of the fundamental constants h and e, respectively. This change crucially relies on the exactness of the relationships which link these constants to measurable quantities. Here we report the first direct comparison of the integer quantum Hall effect in epitaxial graphene with that in GaAs/AlGaAs heterostructures. We find no difference of the quantized resistance value within the relative standard uncertainty of our measurement of 8.6×10 -11 , being the most stringent test of the universality of the quantum Hall effect in terms of material independence.is the measured value from the true value. [International Vocabulary of Metrology,

The half-integer quantum Hall effect in epitaxial graphene is compared with high precision to the well known integer effect in a GaAs/AlGaAs heterostructure. We find no difference between the quantised resistance values within the relative standard uncertainty of our measurement of 8.7 × 10 −11 . The result places new tighter limits on any possible correction terms to the simple relation R K = h/e 2 , and also demonstrates that epitaxial graphene samples are suitable for application as electrical resistance standards of the highest metrological quality. We discuss the characterisation of the graphene sample used in this experiment and present the details of the cryogenic current comparator bridge and associated uncertainty budget.

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An Oxford Instruments Radiox cryogenic radiometer was recently installed at the Bureau International des Poids et Mesures (BIPM). The first measurements were aimed at characterizing the performance of the system. The Radiox was then compared with the cryogenic radiometer of the French Institut National de Métrologie (INM), a CRI LaseRad, at the BIPM by successive measurements of the power in a laser beam at two wavelengths: 647 nm and 476 nm. The radiometers differed in these measurements by 1,9 parts in 10 4 , the uncertainties in each being smaller than 1 part in 10 4 .