Study on the operation of a dual channel digital superconducting quantum interference device with direct‐current‐powered Josephson multiplexer readout

Operation of a dual channel digital superconducting quantum interference device (SQUID) with a dc‐powered Josephson multiplexer (MUX) readout has been observed successfully using a test circuit. In the circuit, output signals of two SQUIDs are digitized by Josephson comparators and read out by the MUX. The noise of the SQUIDs under the operation of the whole circuit is 0.54Φ0/√Hz at 1 kHz. Advantage of using a dc‐powered circuit to realize a low noise SQUID measurement system is confirmed.