Probing Hundreds of Individual Quantum Defects in Polycrystalline and Amorphous Alumina
Probing Hundreds of Individual Quantum Defects in Polycrystalline and Amorphous Alumina
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DOI：
10.1103/physrevapplied.17.034025
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发表时间：
2022-03-09
影响因子：
4.6
通讯作者：
Osborn, Kevin D.
中科院分区：
文献类型：
--
作者：
Hung, Chih-Chiao;Yu, Liuqi;Osborn, Kevin D.
量子二能级系统（TLS）存在于量子比特的材料中，并且被认为是缺陷，因为它们限制了量子比特的相干性。对于超导量子比特，典型的约瑟夫森结势垒是由非晶氧化铝制成的，它承载着TLS。然而，TLS无论是在结构上还是在原子组成上都没有得到普遍的理解。在这项研究中，我们极大地扩展了可用于TLS的定量数据，通过报告的物理偶极矩在两种氧化铝类型：多晶γ-Al 2 O3和非晶α-AlOx。为了获得偶极矩p（z），而不是较少的结构耦合参数g，我们在腔量子电动力学系统中用已知的外部电场调谐单个TLS。我们发现一个明显的差异，从薄膜类型的偶极矩分布，表明TLS结构的差异。从多晶膜类型分析了约400个单独的TLS的大样本。它们沿生长方向p（z）的偶极沿着具有2.6 +/- 0.3德拜（D）（0.54 +/- 0.06 e埃）的平均值和标准偏差σ = 1.6 +/- 0.2 D（0.33 +/- 0.03 e埃）。材料分布很好地拟合于单个高斯函数。从非晶膜中分析了大约200个单独的TLS。平均p（z）= 4.6 +/- 0.5 D（0.96 +/- 0.1 e埃）和σ = 2.5 +/- 0.3 D（0.52 +/- 0.05 e埃）均较大。无定形氧化铝还具有非常大的p（z），大于8.6 D（1.8 e埃），与没有该矩的多晶相比。这些大的时刻只同意基于氧的TLS模型。基于数据和候选模型（离域O和氢基TLS），我们发现多晶氧化铝比非晶氧化铝具有更小的O基和H基TLS的比例。
Quantum two-level systems (TLSs) are present in the materials of qubits and are considered defects because they limit qubit coherence. For superconducting qubits, the quintessential Josephson junction barrier is made of amorphous alumina, which hosts TLSs. However, TLSs are not generally understood, either structurally or in atomic composition. In this study, we greatly extend the quantitative data available on TLSs by reporting on the physical dipole moment in two alumina types: polycrystalline gamma-Al2O3 and amorphous a-AlOx. To obtain the dipole moments p(z), rather than the less-structural coupling parameter g, we tune individual TLSs with a known external electric field in a cavity quantum electrodynamic system. We find a clear difference in the dipole moment distribution from the film types, indicating a difference in TLS structures. A large sample of approximately 400 individual TLSs are analyzed from the polycrystalline film type. Their dipoles along the growth direction p(z) have a mean value of 2.6 +/- 0.3 debye (D) (0.54 +/- 0.06 e angstrom) and standard deviation sigma = 1.6 +/- 0.2 D (0.33 +/- 0.03 e angstrom). The material distribution fits well to a single Gaussian function. Approximately 200 individual TLSs are analyzed from amorphous films. Both the mean p(z) = 4.6 +/- 0.5 D (0.96 +/- 0.1 e angstrom) and sigma = 2.5 +/- 0.3 D (0.52 +/- 0.05 e angstrom) are larger. Amorphous alumina also has very large p(z), greater than 8.6 D (1.8 e angstrom), in contrast to polycrystalline which has none of this moment. These large moments agree only with oxygen-based TLS models. Based on data and the candidate models (delocalized O and hydrogen-based TLSs), we find polycrystalline alumina has smaller ratio of O-based to H-based TLS than amorphous alumina.