Superconducting quantum circuits (SQC) are one of the most promising hardware platforms for quantum computing, yet their performance is currently limited by the presence of various structural defects inside the circuit’s structure. Despite impressive progress in the past decade, a precise understanding of the origin of these defects from various fabrication processes and their impact on coherence is still lacking. In this study, we performed a comprehensive investigation on the microstructure, superconductivity, and resonator quality factor of Nb films deposited by high-power impulse magnetron sputtering (HiPIMS) and direct current (DC) magnetron sputtering. A suite of characterization techniques, including electron microscopy with spectroscopy, secondary ion mass spectrometry, magneto-optical microscopy, and pump-probe reflectivity spectroscopy is used. We reveal that niobium (Nb) resonators fabricated using HiPIMS exhibit a smaller average grain size, thicker surface oxide with larger thickness variations (rougher surface), and a thicker amorphous Nb/Si interface layer compared to samples deposited by DC sputtering. We identified that the amorphous Nb oxides (mainly located at the Nb surface and along the grain boundaries) and Nb-Si amorphous layers (at the Nb/Si interface) are major and potential sources of two-level system (TLS), while off-stochiometric oxides and suboxides of Nb close to the surface, crystalline defects (i.e., dislocations at GB, point defects introduced during deposition) are main contributors of non-TLS sources. Our findings clarify the relationship between different defects and coherence loss mechanisms, highlighting the importance of material microstructure control on performance optimization in SQC.Superconducting quantum circuits (SQC) are one of the most promising hardware platforms for quantum computing, yet their performance is currently limited by the presence of various structural defects inside the circuit’s structure. Despite impressive progress in the past decade, a precise understanding of the origin of these defects from various fabrication processes and their impact on coherence is still lacking. In this study, we performed a comprehensive investigation on the microstructure, superconductivity, and resonator quality factor of Nb films deposited by high-power impulse magnetron sputtering (HiPIMS) and direct current (DC) magnetron sputtering. A suite of characterization techniques, including electron microscopy with spectroscopy, secondary ion mass spectrometry, magneto-optical microscopy, and pump-probe reflectivity spectroscopy is used. We reveal that niobium (Nb) resonators fabricated using HiPIMS exhibit a smaller average grain size, thicker surface oxide with larger thickness variations (rougher surface), and a thicker amorphous Nb/Si interface layer compared to samples deposited by DC sputtering. We identified that the amorphous Nb oxides (mainly located at the Nb surface and along the grain boundaries) and Nb-Si amorphous layers (at the Nb/Si interface) are major and potential sources of two-level system (TLS), while off-stochiometric oxides and suboxides of Nb close to the surface, crystalline defects (i.e., dislocations at GB, point defects introduced during deposition) are main contributors of non-TLS sources. Our findings clarify the relationship between different defects and coherence loss mechanisms, highlighting the importance of material microstructure control on performance optimization in SQC.

Acta MaterialiaJul 4, 202417 citations

The physics of quantum materials

B. Keimer, Joel E. Moore

Nature PhysicsOct 30, 2017514 citations

Properties of an exact crystalline many-body ground state

Peter J. Forrester

Journal of Statistical PhysicsJul 1, 199433 citations

Microscopic Quantum Many-Body Theories and Their Applications

Jesús Navarro, A. Polls

Springer eBooksJan 1, 1998167 citations

Emergence and stability of discrete time-crystalline phases in open quantum systems

Saptarshi Saha, Rangeet Bhattacharyya

Here we provide a theoretical framework to analyze discrete time-crystalline phases (DTC) in open quantum many-body systems. As a particular realization, we choose a quantum many-body system that exhibits cascaded prethermalization . The analysis uses a fluctuation-regulated quantum master equation. The master equation captures the dissipative effects of the drive and dipolar coupling on the dynamics regularized by the thermal fluctuations. We find that the dissipators from the drive and the dipolar interactions lend stability to the dynamics and are directly responsible for the robustness. Specifically, we find that longer fluctuation correlation time enhances the stability of DTC. Our results are in good agreement with the experiments. Finally, we show and quantify how the DTC performance degrades with temperature.Here we provide a theoretical framework to analyze discrete time-crystalline phases (DTC) in open quantum many-body systems. As a particular realization, we choose a quantum many-body system that exhibits cascaded prethermalization . The analysis uses a fluctuation-regulated quantum master equation. The master equation captures the dissipative effects of the drive and dipolar coupling on the dynamics regularized by the thermal fluctuations. We find that the dissipators from the drive and the dipolar interactions lend stability to the dynamics and are directly responsible for the robustness. Specifically, we find that longer fluctuation correlation time enhances the stability of DTC. Our results are in good agreement with the experiments. Finally, we show and quantify how the DTC performance degrades with temperature.

arXiv:2306.14873Jun 26, 20230 citations

Microstructural and preliminary optical and microwave characterization of erbium doped CaMoO $_4$ thin filmsMicrostructural and preliminary optical and microwave characterization of erbium doped CaMoO$_4$ thin films

Ignas Masiulionis, Lin, Bonnie Y. X., Sagar Kumar Seth +10 more

This work explores erbium-doped calcium molybdate (CaMoO $_4$ ) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the $\sim$1.5 $μ$ m Er $^{3+}$ 4f-4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO $_4$ formation that can be in-situ doped with Er (typically 2-100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology; while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO $_4$ films. We perform preliminary optical and microwave characterization on the suspected $Y_1 - Z_1$ transition of 2 ppm, 200 nm epitaxial CaMoO $_4$ annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.This work explores erbium-doped calcium molybdate (CaMoO$_4$) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the $\sim$1.5 $μ$m Er$^{3+}$ 4f-4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO$_4$ formation that can be in-situ doped with Er (typically 2-100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology; while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO$_4$ films. We perform preliminary optical and microwave characterization on the suspected $Y_1 - Z_1$ transition of 2 ppm, 200 nm epitaxial CaMoO$_4$ annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.

arXiv:2508.15122Aug 20, 20250 citations

Microstructural and preliminary optical and microwave characterization of erbium doped CaMoO

_4

thin films

This work explores erbium-doped calcium molybdate (CaMoO

_4

) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the $\sim$1.5

μ

m Er

^{3+}

4f-4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO

_4

formation that can be in-situ doped with Er (typically 2-100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology; while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO

_4

films. We perform preliminary optical and microwave characterization on the suspected

Y_1 - Z_1

transition of 2 ppm, 200 nm epitaxial CaMoO

_4

annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.