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Despite mounting evidence that materials imperfections are a major obstacle to practical applications of superconducting qubits, connections between microscopic material properties and qubit coherence are poorly understood. Here, we combine measurements of transmon qubit relaxation times (T1) with spectroscopy and microscopy of the polycrystalline niobium films used in qubit fabrication. By comparing films deposited using three different techniques, we reveal correlations between T1 and intrinsic film properties such as grain size, enhanced oxygen diffusion along grain boundaries, and the concentration of suboxides near the surface. Qubit and resonator measurements show signatures of two-level system defects, which we propose to be hosted in the grain boundaries and surface oxides. We also show that the residual resistance ratio of the polycrystalline niobium films can be used as a figure of merit for qubit lifetime. This comprehensive approach to understanding qubit decoherence charts a pathway for materials-driven improvements of superconducting qubit performance. Understanding the connection between qubit coherence and microscopic materials properties is vital for improving device performance. Here, the relaxation times of superconducting transmon qubits are found to be directly correlated with Nb film properties such as grain size and surface oxide composition.

The superconducting transmon qubit is a leading platform for quantum computing and quantum science. Building large, useful quantum systems based on transmon qubits will require significant improvements in qubit relaxation and coherence times, which are orders of magnitude shorter than limits imposed by bulk properties of the constituent materials. This indicates that relaxation likely originates from uncontrolled surfaces, interfaces, and contaminants. Previous efforts to improve qubit lifetimes have focused primarily on designs that minimize contributions from surfaces. However, significant improvements in the lifetime of two-dimensional transmon qubits have remained elusive for several years. Here, we fabricate two-dimensional transmon qubits that have both lifetimes and coherence times with dynamical decoupling exceeding 0.3 milliseconds by replacing niobium with tantalum in the device. We have observed increased lifetimes for seventeen devices, indicating that these material improvements are robust, paving the way for higher gate fidelities in multi-qubit processors., Quantum computers based on superconducting transmon qubits are limited by single qubit lifetimes and coherence times, which are orders of magnitude shorter than limits imposed by bulk material properties. Here, the authors fabricate two-dimensional transmon qubits with both lifetimes and coherence times longer than 0.3 milliseconds by replacing niobium with tantalum in the device.

Highly anisotropic and ordered nanoscale lamellar morphologies can be spontaneously generated over macroscopic areas, without the use of a photomask or any templating agents, via the photoelectrodeposition of Se–Te alloy films. To form such structures, the light source can be a single, linearly polarized light source that need not necessarily be highly coherent. In this work, the variation in the morphologies produced by this deposition process was evaluated in response to differences in the coherence and relative phase between multiple simultaneous linearly polarized illumination inputs. Specifically, the morphologies of photoelectrodeposits were evaluated when two tandem same-wavelength sources with discrete linear polarizations, both either mutually incoherent or mutually coherent (with defined phase differences), were used. Additionally, morphologies were simulated via computer modeling of the interfacial light scattering and absorption during the photoelectrochemical growth process. The morphologies that were generated using two coherent, in-phase sources were equivalent to those generated using only a single source. In contrast, the use of two coherent, out-of-phase sources produced a range of morphological patterns. For small out-of-phase addition of orthogonal polarization components, lamellar-type patterns were observed. When fully out-of-phase orthogonal sources (circular polarization) were used, an isotropic, mesh-type pattern was instead generated, similar to that observed when unpolarized illumination was utilized. In intermediate cases, anisotropic lamellar-type patterns were superimposed on the isotropic mesh-type patterns, and the relative height between the two structures scaled with the amount of out-of-phase addition of the orthogonal polarization components. Similar results were obtained when two incoherent sources were utilized. In every case, the long axis of the lamellar-type morphology component aligned parallel to the intensity-weighted average polarization orientation. The observations consistently agreed with computer simulations, indicating that the observed morphologies were fully determined by the nature of the illumination utilized during the growth process. The collective data thus indicated that the photoelectrodeposition process exhibits sensitivity toward the coherency, relative phase, and polarization orientations of all optical inputs and that this sensitivity is physically expressed in the morphology of the deposit.

Inorganic phototropic growth of chalcogen semiconductors wherein a uniform, incoherent, uncorrelated beam of light enables control over the morphology and growth direction of an evolving deposit in three-dimensional space at the nanoscale is explored. Such evolution is similar to natural phototropism exhibited by many photosynthetic plants wherein the physical extension of the biological system proceeds preferentially towards the time-averaged position of the sun. In analogy, during inorganic phototropic growth, a semiconductor material is electrodeposited under illumination and mass is addition is correlated with the spatial distribution of the light absorption. Highly periodic nanostructured films can be generated over macroscopic square centimeter areas in this manner. No laser source, photomask nor structure light field is necessary nor utilized. Additionally, no chemical templating agents (ligands, surfactants) are used. Isotropic morphologies consisting of ordered arrays of nanopores were generated using unpolarized illumination whereas linearly polarized light resulted in highly-anisotropic nanoridge/trough morphologies with the in-plane orientation of the patterns controlled by the direction of the light polarization. The pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the periodicity was found to be sensitive to all investigated tuning of such profiles. Structures with nonequal periodicities in the two orthogonal in-plane directions could also be generated and both periodicities could be independently controlled. Structural complexity correlated with the complexity of optical inputs. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was in fact directed by evolution of the growth interface to maximize anisotropic light collection. This work may be useful for the high-throughput generation of light-trapping absorbers films, photonic elements, and platforms for (photo)electrocatalysts.

Photoelectrochemical growth of Se–Te films spontaneously produces highly ordered, nanoscale lamellar morphologies with periodicities that can be tuned by varying the illumination wavelength during deposition. This phenomenon has been characterized further herein by determining the morphologies of photoelectrodeposited Se–Te films in response to tailored spectral illumination profiles. Se–Te films grown under illumination from four different sources, having similar average wavelengths but having spectral bandwidths that spanned several orders of magnitude, all nevertheless produced similar structures which had a single, common periodicity as quantitatively identified via Fourier analysis. Film deposition using simultaneous illumination from two narrowband sources, which differed in average wavelength by several hundred nanometers, resulted in a structure with only a single periodicity intermediate between the periods observed when either source alone was used. This single periodicity could be varied by manipulating the relative intensity of the two sources. An iterative model that combined full-wave electromagnetic effects with Monte Carlo growth simulations, and that considered only the fundamental light-material interactions during deposition, was in accord with the morphologies observed experimentally. Simulations of light absorption and concentration in idealized lamellar arrays, in conjunction with all of the available data, additionally indicated that a self-optimization of the periodicity of the nanoscale pattern, resulting in the maximization of the anisotropy of interfacial light absorption in the three-dimensional structure, is consistent with the observed growth process of such films.

Electrodeposition of chalcogen alloy films under illumination can spontaneously generate nanopatterned films with significant periodic and multi-dimensional order. The feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern can be controlled by manipulating the input optical excitation. Isotropic morphologies consisting of ordered arrays of nanopores were generated using unpolarized illumination whereas linearly polarized light resulted in highly-anisotropic nanoridge/trough morphologies with the in-plane orientation of the patterns controlled by the direction of the light polarization. The pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the periodicity was found to be sensitive to all investigated tuning of such profiles. Structures with nonequal periodicities in the two orthogonal in-plane directions could also be generated and both periodicities could be independently controlled. Overall structural complexity correlated could be scaled by increasing the complexity of the optical inputs. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was directed by evolution of the growth interface to maximize anisotropic light collection.

Electrodeposition of Se-Te alloy films under illumination spontaneously generates nanopatterned films with significant periodic order. The feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern can be tailored by manipulating the input optical excitation. Isotropic morphologies consisting of ordered arrays of nanopores were generated using unpolarized illumination whereas linearly polarized light resulted in highly-anisotropic nanoridge/trough morphologies with the in-plane orientation of the patterns controlled by the direction of the light polarization. The pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the periodicity was found to be sensitive to all investigated tuning of such profiles. Structures with nonequal periodicities in the two orthogonal in-plane directions could also be generated and both periodicities could be independently controlled. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was directed by evolution of the growth interface to maximize anisotropic light collection.

The template-free growth of well ordered, highly anisotropic lamellar structures has been demonstrated during the photoelectrodeposition of Se-Te films, wherein the orientation of the pattern can be directed by orienting the linear polarization of the incident light. This control mechanism was investigated further herein by examining the morphologies of films grown photoelectrochemically using light from two simultaneous sources that had mutually different linear polarizations. Photoelectrochemical growth with light from two nonorthogonally polarized same-wavelength sources generated lamellar morphologies in which the long axes of the lamellae were oriented parallel to the intensity-weighted average polarization orientation. Simulations of light scattering at the solution-film interface were consistent with this observation. Computer modeling of these growths using combined full-wave electromagnetic and Monte Carlo growth simulations successfully reproduced the experimental morphologies and quantitatively agreed with the pattern orientations observed experimentally by considering only the fundamental light-material interactions during growth. Deposition with light from two orthogonally polarized same-wavelength as well as different-wavelength sources produced structures that consisted of two intersecting sets of orthogonally oriented lamellae in which the relative heights of the two sets could be varied by adjusting the relative source intensities. Simulations of light absorption were performed in analogous, idealized intersecting lamellar structures and revealed that the lamellae preferentially absorbed light polarized with the electric field vector along their long axes. These data sets cumulatively indicate that anisotropic light scattering and light absorption generated by the light polarization produces the anisotropic morphology and that the resultant morphology is a function of all illumination inputs despite differing polarizations.

Electrodeposition of Se-Te alloy films under illumination spontaneously generates nanopatterned films with significant periodic order. The feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern are a function of the exact nature of the optical excitation. Isotropic morphologies consisting of ordered arrays of nanopores were generated using unpolarized illumination whereas linearly polarized light resulted in highly-anisotropic lamellar morphologies with the long axes of the patterns aligned along the E-field vector. The use of two non-orthogonal polarized sources simultaneously generated patterns oriented along the average E-field vector and with degrees of anisotropy related to the difference in orientation between the two input E-field vectors and the phase correlation between the sources. The pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the periodicity was found to be sensitive to all investigated tuning of such profiles. The incidence of the illumination set the direction the material grew from the substrate, mimicking natural phototropism: grazing illumination resulted in growth at significant angle to the surface normal. Also, additional 3D morphological complexity could be directed by utilizing temporal changes in the illumination; for example, zig-zag structures resulted from oscillation of the illumination incidence back and forth across the surface normal and woodpile structures were generated by periodically switching between orthogonal polarization states. The nanopatterning process occurred without the use of any type of physical or chemical templating agents: no photomask, patterned substrate nor surfactants/ligands were used to influence the morphology. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was a consequence of the fundamental light-matter interactions during growth.

Template-free photoelectrodeposition of semiconducting chalcogen alloys resulted in the spontaneous generation of highly periodic nanostructured films over macroscopic length scales. The exact nature of the optical excitation was encoded in the deposit morphology in terms of the feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern. The use of unpolarized light generated isotropic morphologies consisting of ordered arrays of nanopores whereas linearly polarized light resulted in a highly-anisotropic lamellar morphologies with the long axes of the patterns aligned along the E-field vector. Utilization of two same-wavelength, non-orthogonally polarized sources simultaneously generated patterns oriented along the average E-field vector and with degrees of anisotropy related to the difference in orientation between the two input E-field vectors and the phase correlation between the sources. The illumination spectral profile encoded the pattern periodicity and feature width. A single periodicity in a single in-plane direction was consistently observed even with the use of broadband and multimodal spectral profiles and this periodicity was found to be sensitive to all investigated tuning of such profiles. The incidence of the illumination set the direction the material grew from the substrate, mimicking natural phototropism: grazing illumination resulted in growth at significant angle to the surface normal. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition accurately reproduced the experimentally observed morphologies and indicated that the encoding process was a consequence of the fundamental light-matter interactions during growth. This photoelectrochemical deposition process is unique from other methods of generating ordered mesostructures with electrochemical means as no photomask, no photoactive substrate, no lithographic processing, nor any chemical templating agents (ligands, surfactants) were utilized. Illumination was simply conformal over the entire substrate surface (no far-field spatial modulation was used nor required). Complete nanoscale patterning over cm2 areas required only several minutes. Moreover, films were deposited from aqueous solution using oxide precursors at room temperature with low-intensity illumination (~10 mW cm-2). Thus, this process displays significant potential to possibly enable the generation of complex morphologies for functional materials without several limitations imposed by traditional fabrication techniques.

Template-free photoelectrodeposition of semiconducting chalcogen alloys resulted in the spontaneous generation of highly periodic nanostructured films over macroscopic length scales. The exact nature of the optical excitation was encoded in the deposit morphology in terms of the feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern. The use of unpolarized light generated isotropic morphologies consisting of ordered arrays of nanopores whereas linearly polarized light resulted in a highly-anisotropic lamellar morphologies with the long axes of the patterns aligned along the E-field vector. Utilization of two non-orthogonal polarized sources simultaneously generated patterns oriented along the average E-field vector and with degrees of anisotropy related to the difference in orientation between the two input E-field vectors and the phase correlation between the sources. The illumination spectral profile encoded the pattern periodicity and feature width. A single periodicity in single in-plane direction was consistently observed even with the use of broadband and multimodal spectral profiles and the periodicity was found to be sensitive to all investigated tuning of such profiles. The incidence of the illumination set the direction the material grew from the substrate, mimicking natural phototropism: grazing illumination resulted in growth at significant angle to the surface normal. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that the encoding process was a consequence of the fundamental light-matter interactions during growth. This photoelectrochemical deposition process is unique from other methods of generating ordered mesostructures with electrochemical means as no photomask, no photoactive substrate, no lithographic processing, nor any chemical templating agents (ligands, surfactants) were utilized. Moreover, films were deposited from aqueous solution using oxide precursors at room temperature with low-intensity illumination (~10 mW cm-2). Thus, this process displays significant potential to possibly enable the generation of complex morphologies for functional materials without some of the limitations imposed by traditional fabrication techniques.

Photoelectrochemical deposition of semiconducting chalcogenide films resulted in the spontaneous generation of ordered nanostructures wherein the pattern developed is a function of the illumination utilized during growth. Film adopted an ordered, highly anisotropic lamella-type pattern when deposited under conformal illumination with polarized light. Feature size and pitch were controlled the illumination wavelength, direction of anisotropy by the polarization vector and the growth direction by the incident light vector. In order to progress toward generation of intricate, 3-dimensional architectures for specific applications, the manipulation of the pattern formation by utilizing simultaneous illumination from multiple discrete beams during deposition has been investigated. Illumination with two parallel polarized, narrowband sources with two discrete mean wavelengths resulted in patterns with periods that were intermediate of those that would be expected for either source alone and a function of the relative source intensities. The use of two linearly polarized sources with polarization vectors separated by an acute angle produced structures oriented in a direction between the two polarization vectors: this direction was a function of the relative intensities and mean wavelengths of the sources. Illumination with orthogonally polarized sources provided for the generation of mesh-type structures wherein the periodicity and height of pattern in the two orthogonal, in-plane directions could be controlled independently by varying the intensities and wavelengths of the sources. Modeling of the growth was achieved with a Monte Carlo process wherein the probability of mass-addition was weighted based on simulations of the light-matter interactions in the films. This photoelectrochemical deposition process is unique from other methods of generating ordered mesostructures with electrochemical means as no photomask, no photoactive substrate, no physically patterned substrate, nor any chemical templating agents (ligands, surfactants) were utilized. Additionally, tuning the deposition potential and electrolyte along with the illumination has enabled control of the material composition. The same general morphology was observed for a range of varying materials. Thus, this process displays significant, increasing potential to possibly enable the generation of complex morphologies for functional materials without some of the limitations imposed by traditional fabrication techniques.