Quantum Systems

An ultra-wide stopband hairpin bandpass filter with integrated nonuniform transmission lines was designed and fabricated for highly sensitive measurements at cryogenic temperatures down to millikelvin and a frequency range of 10 Hz-10 GHz. The scattering matrices of the filter were characterized at T=4.2 K. The filter provides a stopband from 10 Hz to 2.2 GHz and from 2.3 GHz to 10 GHz with more than 50 dB and 40 dB of amplitude suppression, respectively. The center frequency of the passband is f 0 =2.25 GHz with a bandwidth ∆f=80 MHz. The maximum insertion loss in the passband is 4 dB. The filter has a 50 Ohm input and output impedance, SMA-connector termination and significantly reduced form factor. The wide stopband frequency range, narrow passband in conjunction with small dimensions make the filter suitable for use it as a part of a high sensitive readout for superconducting quantum circuits, such as superconducting quantum bits and cryogenic parametric amplifiers.