Oral Presentation

A prototype of 5-pixel microwave SQUID multiplexer for primordial gravitational wave detection (Remote)

Author(s): Xianfeng Zhou1,2, Zhifa Feng1,2, Qingxiao Ma1,2, Min Li1,2, Peizhan Li1, Wen Zhang1, Jiaqiang Zhong1, Wei Miao1, Jing Li1 and Shengcai Shi1 1Purple Mountain Observatory, Chinese Academy of Sciences, China 2University of Science and Technology of China, China

Presenter: Xianfeng Zhou (Purple Mountain Observatory, Chinese Academy of Sciences, China)

The direct detection of primordial gravitational waves is crucial for understanding the Big Bang model. However, the energy spectrum magnitude is extremely small, in the order of 10⁻¹⁶, making direct detection difficult with the current instruments. However, it is possible to detect the weak imprint left by primordial gravitational waves on the Cosmic Microwave Background (CMB), known as B-MODE, but sophisticated equipment with high sensitivity is required. Superconducting transition-edge sensors (TES) with background-limited sensitivity and large-format arrays have become the preferred detectors for B-mode detection. To reduce the wiring complexity and cost, multiplexing readout techniques have been developed based on superconducting quantum interference devices (SQUID). Microwave SQUID multiplexing (μMUX) with the highest multiplexing factor is suitable for large TES array readout. We are developing μMUX chips for the readout of TES array. As a prototype, we have designed and fabricated a 5-pixel μMUX chip consisting of distributed one-quarter CPW resonator and RF SQUID with a low critical current density of Josephson junction. The measured quality factor of CPW resonator working in the 4.6-5 GHz is higher than 104. Modulation bandwidth is about 250 kHz, compatible with resonator bandwidth. The flux noise is as low as 0.7 μΦ₀/√Hz @ 5 kHz, corresponding to a current noise of 25 pA/√Hz@ 5 kHz.