Single-shot readout of a superconducting qubit using a thermal detector

Measuring the state of a qubit is a key fundamental operation of a quantum computer. High-fidelity single-shot readout of superconducting qubits can be achieved using parametric amplifiers at millikelvin temperatures. However, scaling parametric amplifiers beyond hundreds of qubits is challenging due to practical size and power limitations. Nanobolometers can, in contrast, offer scalability, sensitivity and speed suitable for qubit readout. Here we show that a bolometer can provide single-shot qubit readout with a readout duration of 13.9 mu s and a single-shot fidelity of 0.618. The fidelity is mainly limited by the energy relaxation time of the qubit (28 mu s), and a fidelity of 0.927 is found after removing errors arising from this relaxation. In the future, higher-fidelity single-shot readout may be achieved through improvements in chip design and experimental setup, as well as a change in the bolometer absorber material to reduce the readout time to the level of hundreds of nanoseconds and below. Bolometers can be used for qubit readout, offering a scalable, sensitive and high-speed alternative to current parametric-amplifier-based approaches.