Narrow bandpass cryogenic filter for microwave measurements.

Area of Science:

• Electrical Engineering
• Cryogenic Engineering
• Quantum Computing Hardware

Background:

• Sensitive measurements in superconducting quantum circuits require specialized filters.
• Existing filters may not meet the stringent requirements of millikelvin temperatures and wide frequency ranges.

Purpose of the Study:

• To design and fabricate an ultra-wide stopband hairpin bandpass filter.
• To enable highly sensitive measurements at cryogenic temperatures (down to millikelvin).
• To assess the filter's suitability for superconducting quantum circuits.

Main Methods:

• Design and fabrication of an ultra-wide stopband hairpin bandpass filter with integrated nonuniform transmission lines.
• Characterization of the filter's scattering matrices at T = 4.2 K.
• Evaluation of stopband suppression, passband center frequency, bandwidth, and insertion loss.

Main Results:

• The filter exhibits a wide stopband from 10 Hz to 2.2 GHz (>50 dB suppression) and 2.3 GHz to 10 GHz (>40 dB suppression).
• The passband is centered at 2.25 GHz with an 80 MHz bandwidth and a maximum insertion loss of 4 dB.
• The filter features 50 Ω impedance, SMA connectors, and a reduced form factor.

Conclusions:

• The developed filter is suitable for high-sensitivity readout in superconducting quantum circuits.
• Its wide stopband, narrow passband, and compact size are advantageous for quantum computing applications.
• The filter's performance at cryogenic temperatures makes it a valuable component for quantum technologies.