Low-pass filter with ultra-wide stopband for quantum computing applications

TL;DR

This paper introduces a low-pass filter based on leaky coaxial waveguides with an ultra-wide stopband, minimal pass-band loss, and high attenuation at high frequencies, suitable for quantum computing.

Contribution

A novel leaky coaxial waveguide filter design achieves ultra-wide stopband and low insertion loss, with practical measurements up to 145 GHz for quantum computing applications.

Findings

Insertion loss less than 0.15 dB up to 10 GHz

Attenuation over 60 dB above 70 GHz

Stop band extends to very high frequencies

Abstract

A new type of low-pass filter based on a leaky coaxial waveguide is presented. The filter has minimal insertion loss in the pass band, while at the same time high attenuation in the stop band is achieved. Thanks to its arrangement, the filter does not present parasitic leakage paths, so that, unlike conventional resonant filters, the stop band extends to very high frequencies. It is shown that a particular stop-band attenuation can be obtained by adding or removing leaking sections. Coupling between the center coaxial structure and the leaking holes is investigated. A prototype is manufactured and scattering parameters are measured up to 145 GHz. The prototype shows an insertion loss of less than 0.15 dB up to 10 GHz and an attenuation in excess of 60 dB above 70 GHz. The proposed filter is suitable for superconducting quantum computing applications where qubits are sensitive to radiation with energy high enough to break Cooper-pairs, thereby destroying superconductivity.