Qubit-Based Benchmarking of InP HEMT LNAs: Readout Fidelity Versus Power Consumption

Abstract:High-fidelity single-shot readout of superconducting qubits is essential for fault-tolerant quantum computation. Without a quantum-limited amplifier such as a Josephson parametric amplifier, the cryogenic high-electron-mobility-transistor (HEMT) low-noise amplifier (LNA) at the \SI{4}{K} stage is the dominant noise source in the readout chain. HEMT LNAs are conventionally characterized by Y-factor measurements of the noise temperature $\Tn$, independently of the quantum measurement they ultimately serve. Here we present a qubit-in-the-loop benchmarking method. The method uses the two-dimensional IQ histogram of single-shot readout as a direct figure of merit. We apply it to three state-of-the-art cryogenic InP HEMT LNAs with 53\%, 60\%, and 70\% channel indium content, together with a commercial reference amplifier. The 60\% and 70\% devices have similar $\Tn$ in Y-factor measurements, both lower than the 53\% device. The 70\% device has the highest gain, but qubit readout SNR and assignment fidelity instead peak at 60\%. Using this method, we map assignment fidelity against HEMT LNA dc power consumption for each device. Fidelity does not simply saturate with increasing power. For several devices it declines above a device-dependent power well below typical operating points. For the 60\% device, which has the highest overall fidelity, about \SI{1}{mW} is needed to maintain $\fid > 85\%$. Across all four devices, $\fid > 80\%$ is reached with as little as about \SI{0.3}{mW}, roughly an order of magnitude below typical operating points. These results establish a qubit-referenced benchmarking methodology and provide practical guidance for amplifier selection and bias in power-constrained multi-qubit readout systems.

Quantum Physics (quant-ph); Applied Physics (physics.app-ph)

arXiv:2609.07250 [quant-ph]

(or arXiv:2609.07250v1 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2609.07250 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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