Niobium nanobridge dc SQUID

For the first time high-resolution electron beam contamination lithography has been used to produce active sensing devices. dc SQUID's (Superconducting quantum interference devices) with linewidths as small as 30 nm have demonstrated a minimum intrinsic energy resolution of 3h. This is the best value for any SQUID to date and approaches the limit ≈ h set by the uncertainty principle. The dependence of voltage noise on SQUID parameters is in agreement with a new small-signal model of SQUID noise.