  We report development of a quantum Hall resistance standard accurate to a few
parts in a billion at 300 mK and based on large area epitaxial graphene. The
remarkable precision constitutes an improvement of four orders of magnitude
over the best results obtained in exfoliated graphene and is similar to the
accuracy achieved in well-established semiconductor standards. Unlike the
traditional resistance standards the novel graphene device is still accurately
quantized at 4.2 K, vastly simplifying practical metrology. This breakthrough
was made possible by exceptional graphene quality achieved with scalable
silicon carbide technology on a wafer scale and shows great promise for future
large scale applications in electronics.
