Reverse Isolation and Backaction of the SLUG Microwave Amplifier
Reverse Isolation and Backaction of the SLUG Microwave Amplifier
Fast, accurate measurement of superconducting qubits demands approaching the quantum limit in amplifying weak microwave probe tones. An ideal amplifier would provide $n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ (high forward, negligible reverse) gain, protecting the qubit from noisy downstream measurements. The superconducting low-inductance undulatory galvanometer (SLUG) microwave amplifier provides highly directional gain and minimal backaction …