The high kinetic inductance offered by granular aluminum (grAl) has recently been employed for linear inductors in superconducting high-impedance qubits and kinetic inductance detectors. Because of its large critical current density compared to typical Josephson junctions, its resilience to external magnetic fields, and its low dissipation, grAl may also provide a robust source of nonlinearity for strongly driven quantum circuits, topological superconductivity, and hybrid systems. Having said that, can the grAl nonlinearity be sufficient to build a qubit? Here we show that a small grAl volume ($10\times 200\times 500{\mathrm{nm}}^3$) shunted by a thin film aluminum capacitor results in a microwave oscillator with anharmonicity $\alpha$ two orders of magnitude larger than its spectral linewidth ${\mathrm{\Gamma }}_{01}$, effectively forming a transmon qubit. With increasing drive power, we observe several multiphoton transitions starting from the ground state, from which we extract $\alpha =2\pi \times 4.48\mathrm{MHz}$. Resonance fluorescence measurements of the $|0⟩\to |1⟩$ transition yield an intrinsic qubit linewidth $\gamma =2\pi \times 10\mathrm{kHz}$, corresponding to a lifetime of $16\mu \mathrm{s}$, as confirmed by pulsed time-domain measurements. This linewidth remains below $2\pi \times 150\mathrm{kHz}$ for in-plane magnetic fields up to $\sim 70\mathrm{mT}$.

中文翻译：

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用超导粒状铝实现Transmon Qubit

粒状铝（grAl）提供的高动感电感最近已用于超导高阻抗量子位和动感检测器中的线性电感器。由于与典型的约瑟夫逊结相比，它具有很高的临界电流密度，对外部磁场的弹性以及低的耗散，grAl还可以为强驱动的量子电路，拓扑超导性和混合系统提供强大的非线性源。话虽如此，grAl非线性是否足以构成一个量子位？在这里，我们显示少量的grAl$10\times 200\times 500{\mathrm{纳米}}^3$）被薄膜铝电容器分流导致微波振荡器失谐 $\alpha$ 比光谱线宽大两个数量级 ${\mathrm{\Gamma }}_{01}$，有效形成transmon量子位。随着驱动功率的增加，我们观察到从基态开始的几个多光子跃迁，我们从中提取$\alpha =2\pi \times 4.48\mathrm{兆赫}$。共振荧光测量$|0⟩\to |\mathrm{1个}⟩$ 过渡产生固有的量子位线宽 $\gamma =2\pi \times 10\mathrm{千赫}$，对应于 $16\mu \mathrm{s}$，通过脉冲时域测量得到确认。该线宽保持在以下$2\pi \times 150\mathrm{千赫}$ 适用于平面磁场 $〜70\mathrm{公吨}$。