We describe a superconducting quantum interference device (SQUID) multiplexer operated at microwave frequencies. The outputs of multiple SQUIDs are simultaneously modulated at different frequencies, frequency-division multiplexed, and amplified using a high electron mobility transistor (HEMT). The large bandwidth and dynamic range provided by HEMT amplifiers should make it possible to multiplex a large number of SQUIDs in one output coaxial cable. We measure good SQUID noise performance and demonstrate the multiplexed readout of two dc SQUIDs at different resonant frequencies. In this work dc SQUIDs are used, but this approach is equally applicable to rf SQUIDs.
Applied Physics Letters
HEMT, multiplexer, SQUID
and Lehnert, K.
Microwave SQUID multiplexer, Applied Physics Letters
(Accessed February 23, 2024)