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,

In 2011, the General Conference on Weights and Measures (CGPM) confirmed its intention to adopt new definitions for four of the base units of the SI based on fixed numerical values of selected constants. These will be the kilogram, the ampere, the kelvin and the mole. The CGPM was not able to adopt the new definitions at that time because certain experimental and coordination work was not complete. This paper reviews criteria proposed by the Consultative Committees of the CIPM for such a ‘new SI’ to be adopted and reports on recent progress with work to address them. We also report on work being undertaken to demonstrate that the most important technical aspects of realizing such a new system are practicable. The progress reported here confirms the consensus developing amongst the Consultative Committees and the National Metrology Institutes that it will be possible for the CGPM to adopt these new definitions in 2018.

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.

We present a realization of quantized charge pumping. A lateral quantum dot is defined by metallic split gates in a GaAs/AlGaAs heterostructure. A surface acoustic wave whose wavelength is twice the dot length is used to pump single electrons through the dot at a frequency f = 3 GHz.The pumped current shows a regular pattern of quantization at values I = nef over a range of gate voltage and wave amplitude settings. The observed values of n, the number of electrons transported per wave cycle, are determined by the number of electronic states in the quantum dot brought into resonance with the fermi level of the electron reservoirs during the pumping cycle.

We present a detailed study of the surface acoustic wave mediated quantized transport of electrons through a split-gate device containing an impurity potential defined quantum dot within the split-gate channel. A regime of quantized transport is observed at low rf powers where the surface acoustic wave amplitude is comparable to the quantum dot charging energy. In this regime resonant transport through the single-electron dot state occurs which we interpret as turnstile-like operation in which the traveling wave amplitude modulates the entrance and exit barriers of the quantum dot in a cyclic fashion at GHz frequencies. For high rf powers, where the amplitude of the surface acoustic wave is much larger than the quantum dot energies, the quantized acoustoelectric current transport shows behavior consistent with previously reported results. However, in this regime, the number of quantized current plateaus observed and the plateau widths are determined by the properties of the quantum dot, demonstrating that the microscopic detail of the potential landscape in the split-gate channel has a profound influence on the quantized acoustoelectric current transport.