# Single-Shot Readout of a Superconducting Qubit Using a Thermal Detector

**Authors:** András M. Gunyhó, Suman Kundu, Jian Ma, Wei Liu, Sakari Niemelä, Giacomo Catto, Vasilii Vadimov, Visa Vesterinen, Priyank Singh, Qiming Chen, Mikko Möttönen  
**arXiv:** [2303.03668](https://arxiv.org/abs/2303.03668)  
**Date:** 2023-03-07  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2303.03668v1/

## Key points

- Measuring the state of qubits is crucial in quantum computing
- High-fidelity single-shot readout of superconducting qubits currently relies on parametric amplifiers at low temperatures
- Scaling this technology beyond hundreds of qubits faces challenges due to size and power limitations
- Nanobolometers have shown promise for scalability with sensitivity and speed for qubit readout
- A study by András M. Gunyhó's team at QCD Labs successfully used an ultrasensitive bolometer for single-shot qubit readout
- Achieved a single-shot fidelity of 0.618 with a readout duration of $13.9~\mu\mathrm{s$
- Fidelity limited by the energy relaxation time of the qubit ($T_1 = 28~\mu\mathrm{s$)
- Fidelity increased significantly to 0.927 when accounting for $T_1$ errors
- Simple improvements to chip design and experimental setup could lead to high-fidelity single-shot readout in the future
- Changing bolometer absorber material could reduce readout time to the hundred-nanosecond level, offering potential improvements in quantum computing capabilities

## Summary

In the field of quantum computing, measuring the state of qubits is a crucial operation. Currently, high-fidelity single-shot readout of superconducting qubits relies on parametric amplifiers at extremely low temperatures. However, scaling this technology beyond hundreds of qubits is challenging due to practical limitations in size and power. Recent advancements have shown that nanobolometers possess properties that make them ideal for scalability and have demonstrated promising sensitivity and speed for qubit readout. In a groundbreaking study conducted by András M. Gunyhó and his team at QCD Labs, Aalto University, they successfully utilized an ultrasensitive bolometer as an alternative to parametric amplifiers for single-shot qubit readout. The experiment achieved a remarkable single-shot fidelity of 0.618 with a modest readout duration of $13.9~\mu\mathrm{s}$. This fidelity was primarily limited by the energy relaxation time of the qubit ($T_1 = 28~\mu\mathrm{s}$). When accounting for $T_1$ errors, the fidelity increased significantly to 0.927. The researchers believe that with simple improvements to chip design and experimental setup, high-fidelity single-shot readout could be achieved in the future. One particularly intriguing avenue for improvement involves changing the bolometer absorber material to reduce the readout time to the hundred-nanosecond level. This study not only demonstrates the potential of using thermal detectors like bolometers for qubit readout but also opens up new possibilities for enhancing quantum computing capabilities through innovative technological advancements.