Thermal-noise metrics for quantum-system interconnects

Experimental investigation of microwave photon noise [1,2] in quantum-system interconnects is crucial due to its detrimental impact on quantum measurements e.g. coherence of superconducting qubits.

In this talk, we first display coherence measurements of a transmon qubit [3] which exhibits large uncertainty in inferred blackbody temperatures. Such data highlight the need of methods for qualifying interconnects to obtain metrics agnostic to the device, its readout line, or shielding.

Second, to target this problem, we demonstrate a bolometric method for quantifying thermal noise from control lines, i.e. blackbody temperature and thermal time constant [2]. Specifically, we connect the lines to a coaxially-coupled nanobolometer [4], calibrated with a variable-temperature blackbody noise source [5], allowing precise measurements of incident thermal radiation power and thermal latencies. We apply our method to specific examples including coaxial wiring and flexible printed circuits.



[1] Phys. Rev. X 10, 041054

[2] PRX Quantum 5, 030302

[3] Appl. Phys. Lett. 124, 224001 (2024)

[4] Phys. Rev. Lett. 117, 030802

[5] Rev. Sci. Instrum. 92, 034708 (2021)