Thermalization of a flexible microwave stripline measured by a superconducting qubit

TL;DR

This study demonstrates that flexible microwave striplines can effectively thermalize at cryogenic temperatures, maintaining low residual photon populations and qubit temperatures comparable to traditional cables, thus enabling higher cabling density in cryogenic quantum systems.

Contribution

We experimentally verify the thermalization performance of flexible microwave striplines using a superconducting qubit, showing comparable thermalization times and qubit temperatures to conventional cables.

Findings

Flexible striplines achieve 0.28 ms thermalization time.

Residual photon population below 3.5e-3 photons.

Qubit temperature close to cryostat base temperature.

Abstract

With the demand for scalable cryogenic microwave circuitry continuously rising, recently developed flexible microwave striplines offer the tantalyzing perspective of increasing the cabling density by an order of magnitude without thermally overloading the cryostat. We use a superconducting quantum circuit to test the thermalization of input flex cables with integrated $60\,$dB of attenuation distributed at various temperature stages. From the measured decoherence rate of a superconducting fluxonium qubit, we estimate a residual population of the readout resonator below $3.5\cdot10^{-3}$ photons and we measure a $0.28\,$ms thermalization time for the flexible stripline attenuators. Furthermore, we confirm that the qubit reaches an effective temperature of $26.4\,$mK, close to the base temperature of the cryostat, practically the same as when using a conventional semi-rigid coaxial cable setup.