基于量子比特的InP HEMT低噪声放大器基准测试：读出保真度与功耗的权衡

中文摘要 AI 辅助

高保真度的超导量子比特单次读出对于容错量子计算至关重要。在没有诸如约瑟夫森参量放大器等量子极限放大器的情况下，位于4K温区的低温高电子迁移率晶体管（HEMT）低噪声放大器（LNA）是读出链路中的主要噪声源。HEMT LNA通常通过Y因子法测量噪声温度$T_n$来表征，这与它们最终服务的量子测量无关。在此，我们提出了一种量子比特在环的基准测试方法。该方法使用单次读出的二维IQ直方图作为直接性能指标。我们将其应用于三款具有53%、60%和70%沟道铟含量的最先进的低温InP HEMT LNA，以及一款商用参考放大器。在Y因子测量中，60%和70%器件的$T_n$相近，均低于53%器件。70%器件具有最高增益，但量子比特读出信噪比和分配保真度却在60%器件中达到峰值。使用该方法，我们绘制了每个器件的分配保真度与HEMT LNA直流功耗的关系图。保真度并非随功率增加而简单饱和。对于几个器件，在低于典型工作点的器件特定功率之上，保真度会下降。对于整体保真度最高的60%器件，维持$fid > 85\%$约需1mW功率。在所有四个器件中，仅需约0.3mW即可达到$fid > 80\%$，这比典型工作点低约一个数量级。这些结果建立了一种以量子比特为参照的基准测试方法，并为功率受限的多量子比特读出系统中的放大器选择和偏置提供了实用指导。

英文摘要

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 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 $T_N$, 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 $T_N$ in Y-factor measurements, both lower than the 53\% device. The 70\% device has the highest gain, but qubit readout SNR and assignment fidelity $\mathcal{F}_a$ instead peak at 60\%. Using this method, we map $\mathcal{F}_a$ against HEMT LNA dc power consumption for each device. $\mathcal{F}_a$ 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 $\mathcal{F}_a$, about 1~mW is needed to maintain $\mathcal{F}_a > 85\%$. Across all four devices, $\mathcal{F}_a > 80\%$ is reached with as little as about 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.

发表机构

• Chalmers Next Labs AB（查尔姆斯Next实验室有限公司）

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