Towards ultra-sensitive SQUIDs based on sub-micrometer-sized Josephson Junctions

We recently demonstrated a first-order axial gradiometer SQUID system, which is operated in a liquid He dewar with negligible noise contribution. The achieved close to SQUID limited measured coupled energy sensitivity ε of ~ 30 h corresponds to a white field noise below 180 aT Hz-1/2. In order to further improve the SQUID noise performance, the junction capacitance was reduced by decreasing its la...