Identifying candidate hosts for quantum defects via data mining

Atom-like defects in solid-state hosts are promising candidates for the development of quantum information systems, but despite their importance, the host substrate/defect combinations currently under study have almost exclusively been found serendipitously. Here we systematically evaluate the suitability of host materials by applying a combined four-stage data mining and manual screening process to all entries in the Materials Project database, with literature-based experimental confirmation of band gap values. We identify 580 viable host substrates for quantum defect introduction and use in quantum information systems. While this constitutes a significant increase in the number of known and potentially viable material systems, it nonetheless represents a significant (99.54%) reduction from the total number of known inorganic phases, and the application of additional selection criteria for specific applications will reduce their number even further. The screening principles outlined may easily be applied to previously unrealized phases and other technologically important materials systems.Comment: Currently under consideration at npj Computational Material

Signature of an Ultrafast Photo-Induced Lifshitz Transition in the Nodal-Line Semimetal ZrSiTe

Here we report an ultrafast optical spectroscopic study of the nodal-line semimetal ZrSiTe. Our measurements reveal that, converse to other compounds of the family, the sudden injection of electronic excitations results in a strongly coherent response of an $A_{1g}$ phonon mode which dynamically modifies the distance between Zr and Te atoms and Si layers. "Frozen phonon" DFT calculations, in which band structures are calculated as a function of nuclear position along the phonon mode coordinate, show that large displacements along this mode alter the material's electronic structure significantly, forcing bands to approach and even cross the Fermi energy. The incoherent part of the time domain response reveals that a delayed electronic response at low fluence discontinuously evolves into an instantaneous one for excitation densities larger than $3.43 \times 10^{17}$ cm$^{-3}$. This sudden change of the dissipative channels for electronic excitations is indicative of an ultrafast Lifshitz transition which we tentatively associate to a change in topology of the Fermi surface driven by a symmetry preserving $A_{1g}$ phonon mode

Transient Drude Response Dominates Near-Infrared Pump–Probe Reflectivity in Nodal-Line Semimetals ZrSiS and ZrSiSe

The ultrafast optical response of nodal-line semimetals ZrSiS and ZrSiSe was studied in the near-infrared using transient reflectivity. The materials exhibit similar responses, characterized by two features, well-resolved in time and energy; the first decays after hundreds of femtoseconds, and the second lasts for nanoseconds. Using Drude–Lorentz fits of the materials’ equilibrium reflectance, we show that these are well-represented by a sudden change of the electronic properties (increase of screening or reduction of the plasma frequency) followed by an increase of the Drude scattering rate. This directly connects the transient data to a physical picture in which carriers, after excitation into the conduction band, return to the valence band by sharing excess energy with the phonon bath, resulting in a hot lattice that relaxes through slow diffusive processes. The emerging picture reveals that the sudden electronic reorganization instantaneously modifies the materials’ electronic properties on a time scale not compatible with electron–phonon thermalization

Erbium-implanted materials for quantum communication applications

Erbium-doped materials can serve as spin-photon interfaces with optical transitions in the telecom C band, making them an exciting class of materials for long-distance quantum communication. However, the spin and optical coherence times of Er3+ ions are limited by currently available host materials, motivating the development of new Er3+-containing materials. Here we demonstrate the use of ion implantation to efficiently screen prospective host candidates, and show that disorder introduced by ion implantation can be mitigated through post-implantation thermal processing to achieve inhomogeneous linewidths comparable to bulk linewidths in as-grown samples. We present optical spectroscopy data for each host material, which allows us to determine the level structure of each site, allowing us to compare the environments of Er3+ introduced via implantation and via doping during growth. We demonstrate that implantation can generate a range of local environments for Er3+, including those observed in bulk-doped materials, and that the populations of these sites can be controlled with thermal processing

Tunable W⁵⁺ Absorbance in Laser Floating Zone Grown Bismuth Tungstate

Bi2WO6 has been actively investigated as a viable photocatalysis substitute for TiO2. This along with progress in designing qubit hosts using W5+ centers encourages the development of single crystal growths of this material using the floating zone technique. Single crystals of Bi2WO6–x were grown using a laser diode floating zone furnace. Laue diffraction and single crystal X-ray diffraction confirm development of single crystalline domains. Williamson–Hall analysis shows annealed floating zone crystals contain less strain compared to unannealed and flux grown samples. Fitting of the heat capacity data shows two optical phonon modes modeled by Einstein oscillators, with the lower energy oscillator decreasing post annealing. The band gap is estimated as 2.6 eV using hyperspectral imaging, showing an additional absorption band present in the oxygen-deficient samples compared to those grown via flux. This additional absorption is tunable via annealing post growth. Overall, this technique demonstrates the feasibility of growing large single crystals of Bi2WO6 with tunable W5+ centers for potential application in photocatalysis and quantum information