Improved Design of Integrated Quantum Voltage Noise Source

We present the design improvement of an integrated quantum voltage noise source (IQVNS) aimed at low-cost user-friendly Johnson noise thermometers with high accuracy. A problem in our previous design of the IQVNS was mainly associated with lax synchronization with low- and high-frequency clock signals, making the whole system complicated and less robust. We have employed on-chip generation of low-frequency clocks by downconverting a high-frequency reference clock so that the whole IQVNS operates with a single clock. Counterflow-clocking architecture has been introduced both in chip- and subsystem-level pipelines for achieving wider timing margins. The improved IQVNS has been fabricated by using our standard niobium-junction technology and successfully tested.