Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA.
Phys Rev Lett. 2013 Aug 9;111(6):065901. doi: 10.1103/PhysRevLett.111.065901. Epub 2013 Aug 8.
We perform ab initio calculations of hydrogen-based tunneling defects in alumina to identify deleterious two-level systems (TLS) in superconducting qubits. The defects analyzed include bulk hydrogenated Al vacancies, bulk hydrogen interstitial defects, and a surface OH rotor. The formation energies of the defects are first computed for an Al- and O-rich environment to give the likelihood of defect occurrence during growth. The potential energy surfaces are then computed and the corresponding dipole moments are evaluated to determine the coupling of the defects to an electric field. Finally, the tunneling energy is computed for the hydrogen defect and the analogous deuterium defect, providing an estimate of the TLS energy and the corresponding frequency for photon absorption. We predict that hydrogenated cation vacancy defects will form a significant density of GHz frequency TLSs in alumina.
我们进行了基于氢的氧化铝隧道缺陷的从头算计算，以识别超导量子比特中有害的两能级系统（TLS）。分析的缺陷包括体氢化 Al 空位、体氢间隙缺陷和表面 OH 转子。首先计算了富 Al 和富 O 环境中缺陷的形成能，以给出在生长过程中缺陷发生的可能性。然后计算了势能面，并评估了相应的偶极矩，以确定缺陷与电场的耦合。最后，计算了氢缺陷和类似的氘缺陷的隧道能，提供了 TLS 能量和相应光子吸收频率的估计。我们预测，氢化阳离子空位缺陷将在氧化铝中形成大量 GHz 频率的 TLS。
