03 Jul Tests at Chalmers confirm QueSt suitability for thermally sensitive quantum environments

Recent tests from Chalmers University of Technology have demonstrated that the QueSt switch prototype can operate without introducing thermal disturbances in superconducting quantum processors – this represents a critical step toward scalable quantum computing.

Superconducting quantum processing units (QPUs) require ultra-low temperatures (below 30 mK) to maintain coherence and operate reliably. However, residual thermal photons in the readout resonator—especially those propagating from high-temperature amplification components—can lead to qubit dephasing, compromising performance.

To address this, the Spectrum team explored an innovative architecture that replaces bulky and magnetic commercial isolators with a cryogenic switch (QueSt), designed to decouple the QPU from the noisy amplification chain during idle phases. While the first prototype of QueSt does not yet achieve the required isolation levels (>35 dB) to replace current isolators, it demonstrated a key advantage: zero thermal impact on the qubit environment during switching.

Using a sophisticated qubit-based thermometry technique, researchers monitored changes in radiation field temperature during QueSt switching events. They found that the switch did not cause any measurable heating, maintaining a stable temperature of 60 mK. In contrast, a commercial switch raised the temperature to 170 mK with very slow recovery.

This finding confirms that QueSt is thermally compatible with quantum systems and lays the groundwork for further improving its isolation performance. Once refined, such switches could enable more compact, low-noise, and scalable cryogenic setups for quantum computing.