Bolometric readout of superconducting qubits, Part 1/2*

Measuring the state of qubits is a fundamental operation in quantum computing, quantum error correction, and quantum communication. Recently, nanobolometers have been developed that allow the thermal detection of a low number of microwave photons [1,2]. We use such a bolometer in place of a parametric amplifier (paramp) in a dispersive-readout setup to measure the state of a superconducting qubit.

Compared to a paramp, which is usually pumped near the qubit and readout resonator frequencies at several gigahertz, the bolometer pump is far detuned from the qubit and resonator at 600 MHz. This avoids the need for isolators between the readout resonator and the bolometer. In addirion, the power of the bolometer pump tone is orders of magnitude lower than what is typically required for paramps.

In Part 1/2, we demonstrate basic qubit characterization experiments followed by single-shot readout. We also present a path towards improving the readout fidelity. In Part 2/2, we discuss multiplexed readout using mulitple bolometers.

[1] Kokkoniemi, R., et al. Commun Phys 2, 124 (2019). https://doi.org/10.1038/s42005-019-0225-6

[2] Kokkoniemi, R., et al. Nature 586, 47–51 (2020). https://doi.org/10.1038/s41586-020-2753-3