Poly- and single-crystalline diamond nitrogen-induced TLS losses estimation with superconducting lumped elements micro-resonators

TL;DR

This paper investigates ultra-low dielectric losses in diamond materials at sub-Kelvin temperatures using superconducting micro-resonators, revealing how nitrogen content and growth processes affect TLS losses relevant for quantum and high-power applications.

Contribution

It introduces a high-sensitivity method using superconducting micro-resonators to evaluate dielectric losses in diamond, linking nitrogen incorporation and growth processes to TLS-induced losses.

Findings

Higher nitrogen content correlates with increased dielectric losses.

Growth processes influence defect incorporation and loss mechanisms.

Superconducting micro-resonators offer superior sensitivity over traditional methods.

Abstract

Research on diamond has intensified due to its exceptional thermal, optical, and mechanical properties, making it a key material in quantum technologies and high-power applications. Diamonds with engineered nitrogen-vacancy (NV) centers represent a very sensitive platform for quantum sensing, while high-optical quality diamond windows represent a fundamental safety component inside Electron Cyclotron Resonance Heating (ECRH) systems in nuclear fusion reactors. A major challenge is the development of ultra-low-loss, high-optical-quality single-crystal diamond substrates to meet growing demands for quantum coherence and power handling. Traditionally, dielectric losses ($\tan \delta$) in diamonds are evaluated using Fabry-Perot microwave resonators, in which the resonance quality factors Q of the cavity with and without the sample are compared. These devices are limited to resolutions around 10$^{-5}$ by the need to keep the resonator dimensions within a reasonable range. In contrast, superconducting thin-film micro-strip resonators, with Q factors exceeding 10$^6$, are stated to provide higher sensitivity for assessing ultra-low-loss materials. This study examines four diamond samples grown through different processes, analyzing their dielectric losses at extreme low temperatures (sub-Kelvin) within the Two-Level System (TLS) framework. Complementary Raman spectroscopy measurements allowed us not only to associate higher nitrogen content with increased losses, but also to investigate how the different growth process influence the way these defects are incorporated in the crystal lattice.