Precision measurement of the microwave dielectric loss of sapphire in the quantum regime with parts-per-billion sensitivity

Abstract

Dielectric loss is known to limit state-of-the-art superconducting qubit lifetimes [1]. Recent experiments imply upper bounds on bulk dielectric loss tangents on the order of 100 parts-per-billion [2-4], but because these inferences are drawn from fully fabricated devices with many loss channels, they do not definitively implicate or exonerate the dielectric. To resolve this ambiguity, we have devised a measurement method capable of separating and resolving bulk dielectric loss with a sensitivity at the level of 5 parts-per-billion. The method, which we call the dielectric dipper, involves the in-situ insertion of a dielectric sample into a high-quality microwave cavity mode. Smoothly varying the sample's participation in the cavity mode enables a differential measurement of the sample's dielectric loss tangent. The dielectric dipper can probe the low-power behavior of dielectrics at cryogenic temperatures, and does so without the need for any lithographic process, enabling controlled comparisons of substrate materials and processing techniques. We demonstrate the method with measurements of EFG sapphire, from which we infer a bulk loss tangent of 62(7) × 10 −9 and a substrate-air interface loss tangent of 12(2) × 10 −4 [5]. For a typical transmon [1], this bulk loss tangent would limit device quality factors to Q 20 million, suggesting that bulk loss is likely the dominant loss mechanism in the longest-lived transmons on sapphire [2,3]. We also demonstrate this method on HEMEX sapphire and bound its bulk loss tangent to be less than 15(5) × 10 −9 . As this bound is about four times smaller than the bulk loss tangent of EFG sapphire, use of HEMEX sapphire as a substrate would lift the bulk dielectric coherence limit of a typical transmon qubit to several milliseconds.

Scaling superconducting quantum chip with highly integratable quantum building blocks

“…Superconducting quantum computing chips have garnered significant attention from researchers due to their high design flexibility and the potential for large-scale fabrication. In recent years, there has been extensive and systematic investigation into the quantum coherence mechanism [1][2][3], circuit device coupling [4][5][6], material interaction [7][8][9], and information transfer within this system, leading to notable advances in these fields. Nowadays, researchers implement higher precision gate operations [10,11] and demonstrative calculations of some typical quantum algorithms [12].…”

Chemical profiles of the oxides on tantalum in state of the art superconducting circuits

“…The lifetimes of current 2D transmons are believed to be limited by microwave dielectric losses [12,13]. Recent work has measured the dielectric loss tangent of high-purity bulk sapphire as 15(5) × 10 −9 at qubit operating conditions [14]. This loss tangent would result in a qubit lifetime of several milliseconds if it were the only source of dielectric loss, suggesting that losses are dominated by uncontrolled defects at surfaces and interfaces or by material contaminants [15].…”