Thermal noise and qubit addressability

We present quantitative, device-independent measurements of power radiated to a quantum processor through its control lines using a sensitive time-resolving coaxialy-coupled thermal detector [1]. The method enables us to compare thermal noise emitted by attenuated coaxial cables and novel flexible printed circuit cables. Our data, interpreted through an open quantum system model, reveals the interplay between dissipated signal power, transmon-qubit lifetime, pure dephasing, gate fidelity, and decoherence rates due to self-heating during microwave operations. A key advantage of our detection scheme is its ability to detect noise generated during active self-heating in cables during state-control or readout. These results underscore the importance of cryogenics in balancing qubit addressability and coherence.

[1] Slawomir Simbierowicz, Massimo Borrelli, Volodymyr Monarkha, Ville Nuutinen, and Russell E. Lake, Inherent Thermal-Noise Problem in Addressing Qubits PRX Quantum 5, 030302 (2024)