Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T72: New Approaches for Spins and EmittersFocus Recordings Available
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Sponsoring Units: DMP Chair: Huan Zhao, Los Alamos National Lab Room: Hyatt Regency Hotel -Jackson Park D |
Thursday, March 17, 2022 11:30AM - 12:06PM |
T72.00001: Active Space Wavefunction Methods for Defects in Solids Invited Speaker: John P Philbin Quantum embedding theories offer a means to combine multiple levels of electronic structure theory in order to predict accurate electronic properties of correlated materials. These methods can correct errors in low-level theories, such as the delocalization error in density functional theory or the lack of electron correlation in Hartree-Fock theory. In this work, we develop a purely wavefunction based approach to quantum embedding in order to compute correlated electronic states of systems with weak to strong correlations within spatially localized embedded fragments. Furthermore, we benchmark various active space wavefunction methods (CASSCF, CCSD, etc.) for quantum defects in solids. |
Thursday, March 17, 2022 12:06PM - 12:18PM |
T72.00002: Extrinsic and Intrinsic Defects in MgO and CaO as potential spin-qubit candidates Christian W Vorwerk, Nan Sheng, Marco Govoni, Giulia Galli Several point defects in diamond, SiC, and h-BNhave been recently proposed as promising platforms to realize spin qubits. Here we extend the search of spin qubits to insulating oxides, as simple point defects in some binary and ternary oxides have been predicted to exhibit long coherence times [1]. We focus on intrinsic and extrinsic defects in MgO and CaO and present results for their structural, electronic, and optical properties. We consider the ubiquitous intrinsic oxygen and magnesium vacancies, and some of their complexes, and transition-metal and rare-earth dopants. To predict the strongly correlated excitations of these defects, we use the quantum defect embedding theory, an embedding approach that combines many-body perturbation theory to describe the valence electrons, with full-configuration interaction for the correlated electrons localized at the defect site [2]. |
Thursday, March 17, 2022 12:18PM - 12:30PM |
T72.00003: Efficient Characterization of Features in Micro-Photoluminescence Images for the Identification of Single-Photon Emitters Leah Narun, Rebecca Fishman, Henry Shulevitz, Raj Patel, Lee Bassett Solid-state single-photon emitters (SPE) are a basis for quantum technologies. However, there are many potential SPE that have yet to be explored. The discovery of new SPE typically relies on time-consuming techniques for identifying point source emitters by eye in 2-dimensional (2D) photoluminescence (PL) scans. This manual strategy is a bottleneck for discovering new SPE, suggesting a need for a more efficient method for SPE discovery. Here we present a quantitative method using image analysis and regression fitting to automatically identify Gaussian emitters in 2D PL scans and classify them according to their intensity and stability. We demonstrate efficient emitter classification for nanodiamond arrays and hexagonal boron nitride (hBN) flakes. Flexible criteria detect SPE in both samples despite variation in emitter intensity, stability, and background quality. The detection criteria can be tuned to unique material systems and experimental setups to accommodate the diverse properties of SPE. |
Thursday, March 17, 2022 12:30PM - 1:06PM |
T72.00004: Emerging rare-earth doped materials for quantum information Invited Speaker: Elizabeth A Goldschmidt Optically active and highly coherent emitters in solids are a promising platform for a wide variety of quantum information applications, particularly quantum memory and other quantum networking tasks. Rare-earth atoms, in addition to having record long coherence times, have the added benefit that they can be hosted in a wide range of solid-state materials. We can thus target particular materials (and choose particular rare-earth species and isotopes) that enable certain application-specific functionalities. I will discuss several ongoing projects with rare-earth atoms in different host materials and configurations. This includes investigations of inhomogeneous broadening in rare-earth ensembles, which is highly host-dependent and plays an important role in the quantum memory protocols that can be implemented in any given system. I will present results on our efforts to identify and grow new materials with rare-earth atoms at stoichiometric concentrations in order to reduce the disorder-induced inhomogeneous broadening. I will also discuss our work investigating photonic integration of rare-earth doped samples that aims to increase the light-atom interaction for practical quantum devices. I will show results from our work with rare-earth atom dopants in thin-film lithium niobate, which admits standard nanofabrication techniques, and show the suitability of this platform for quantum applications. |
Thursday, March 17, 2022 1:06PM - 1:18PM |
T72.00005: Terahertz nano-imaging of heterogeneous dipole fields and charge scattering at a single nanojunction Samuel J Haeuser, Richard Kim, Joongmok Park, Lin Zhou, Matthew J Kramer, Mark Field, Cameron J Kopas, Josh Y Mutus, Jin-Su Oh, Jigang Wang Decoherence in quantum states and the introduction of errors from cumulative gate operations are the main obstacles that need to be overcome to achieve full-scale quantum computing with superconducting qubits. To address such issues, it is thus imperative to identify and correlate electronic-photonic heterogeneity from interface and boundary imperfections in Josephson junctions, the key element in qubit devices. Here we discover and directly visualize interface nano-dipole near fields from terahertz (THz) light-junction coupling. Our results show a remarkable asymmetry in charge scattering across the junction that correlates with broken boundaries from the sequential lithographic steps in the Josephson junction fabrication. Near-field imaging of heterogeneous electrodynamics underpins distinguishing features that are absent in responses from topographic steps. The nano-THz probe of junction dipole fields at space-frequency limits represents a powerful and non-invasive tool to capture and leverage materials loss and decoherence in qubit devices. |
Thursday, March 17, 2022 1:18PM - 1:30PM |
T72.00006: Instability of rock-salt cubic NbN in density functional calculations Anuj Goyal, Sage Bauers, Stephan Lany All-nitride semiconductor/superconductor heterojunctions utilizing cubic niobium nitride (NbN) are a promising approach to superconducting quantum circuits for next-generation quantum-information systems. However, there are fundamental open questions on the atomic structure of NbN. In calculations with several levels of density functional theory (DFT), we find that the cubic rocksalt structure NbN (Fm-3m, 225) is energetically very unstable against the ground state hexagonal NbN in a tungsten carbide (P-6m2, 187) type lattice. To better understand the appearance of a cubic phase in numerous experiments, we perform a DFT study on possible NbN structures, determining the energy ordering between different polymorphs from databases and structure prediction. We perform supercell calculations of disordered NbN, finding that the rocksalt structure is dynamically unstable and relaxes to a lower energy monoclinic phase (C2/m, 12), which retains an approximate average cubic symmetry. However, the associated energy gain is not substantial enough for a plausible explanation for cubic NbN. We further investigate the role of external factors such as in-plane strain during epitaxial growth as well as the presence of off-stoichiometry and impurity doping on the energy ordering. |
Thursday, March 17, 2022 1:30PM - 1:42PM |
T72.00007: Si-integrated BaTiO3 modulators for Quantum Computing with Si photonics Alexander A Demkov, Agham Posadas, Daniel Wassertman, Zuoming Dong Silicon is essentially transparent above 1300 nm and can be machined into practically any shape with extremely high precision and with minimal surface roughness. These two properties make it extremely attractive for fabricating waveguides operating at the telecom wavelength of 1550 nm, making a natural connection between the optical fiber and Si chip. Silicon photonics has many applications, including in quantum information sciences. One of the key elements of this emergent technology is the integrated electro-optical modulator (Mach Zehnder interferometer (MZI) or ring resonator). I will discuss our recent work on integrating ferroelectric BaTiO3 (BTO) with Si photonics to make integrated electro-optical modulators using the linear electro optic or Pockels effect for applications in optical quantum computing. |
Thursday, March 17, 2022 1:42PM - 1:54PM |
T72.00008: Modeling the Optical Properties of Hidden Silicon-Vacancy Centers in Diamond Tommy Wen J Chin, Christopher L Smallwood Investigations into the dynamics of a high-density sample of negatively charged silicon-vacancy (SiV-) centers in diamond have recently led to the discovery of a "hidden" population of SiV- centers that is not typically observed under photoluminescence, but which nevertheless exhibits interesting electronic coherence properties [1]. The hidden SiV- center population is also much more spectrally inhomogeneous than its photoluminescing counterpart in the same sample, indicating the likely impact of strain. Despite this, the detailed mechanism by which strain reduces photoluminescence intensity and affects electronic coherence times remains unknown. In this talk, we summarize the development of a theoretical model, based on density matrix perturbation theory, that explains the origin of the hidden-center population's properties by means of interactions involving a nonradiative dark state. Results may have implications for color-center based quantum devices and the development of quantum networks. |
Thursday, March 17, 2022 1:54PM - 2:06PM |
T72.00009: Experimental and Computational Investigations of Boron-Nitrogen Pairs in Diamond for Quantum Information Applications Anil Bilgin, Jeremy Estes, Ian N Hammock, Hannes Bernien, Alexander A High, Giulia Galli Donor-acceptor pairs (DAP) in semiconductors that exhibit large electric dipole moments in their ground and excited states are promising candidates that could enable new functionalities in solid state quantum information science. We investigate substitutional Boron and Nitrogen defects and how they form DAP in diamond using density functional theory (DFT). Zero phonon lines (ZPL) of each DAP shell with increasing interdefect distance is computed and the Coulombic nature of the electron-hole interaction that dominates the emission spectrum is captured. We use formation energy diagrams to understand the charge state transitions in the system. We compute the differences in polarization between ground and excited states using maximally localized Wannier functions, which show unusually large electric dipole moments. We explore the effect of an external electric field to make use of these large dipole moments to tune ZPL energies in a broad range. We explicitly calculate a correction term for DAP that have overlapping Bohr radii. We complement our computational results with photoluminescence experiments on diamond samples implanted with Boron and Nitrogen. Our results indicate that Boron and Nitrogen in diamond are suitable candidates for such DAP that show a broad range of tunability. |
Thursday, March 17, 2022 2:06PM - 2:18PM |
T72.00010: Beryllium oxide as a host for quantum defects YUBI CHEN, Mark E Turiansky, Chris G Van de Walle The large bandgap of BeO, which exceeds 10 eV, makes BeO a promising host for quantum defects. We have performed a comprehensive first-principles study of the native point defects in BeO, using density functional theory with the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE). We investigated various properties of BeO native defects, including the atomic geometries, orbital structure, spin properties, and optical properties. The Fermi level of pure BeO is pinned near midgap based on charge neutrality of the native defects. We found that the beryllium and oxygen vacancies are the most stable native defects in BeO, while other native defects like interstitials or antisites are high in formation energy. Based on our survey, we identified defects with electron states well separated from the band edges that are potential quantum defects. We found that the neutral beryllium vacancy, which has similarities to the NV center in diamond, may have desirable optical sensing applications due to its large electron-phonon coupling. |
Thursday, March 17, 2022 2:18PM - 2:30PM |
T72.00011: Decoherence of nitrogen-vacancy spin ensembles in diamond in the nitrogen electron-nuclear spin bath Huijin Park, Junghyun Lee, Sangwook Han, Sangwon Oh, Hosung Seo Nitrogen-vacancy (NV) centers in diamond have been developed into essential hardware units to develop a wide range of solid-state quantum technologies [1]. For such applications, the long coherence time of NV centers is crucial. Numerous previous studies identified that the NV’s decoherence is often governed by the magnetic noise produced by the 13C nuclear spin bath and the nitrogen (P1) electron spin bath in a diamond. While the 13C-induced decoherence has been well understood, the understanding of the P1-driven decoherence is still incomplete. In this study, we aim at a systematic investigation on the P1-driven decoherence of NV ensembles with varying P1 concentrations from 1ppm to 100ppm by combining cluster correlation expansion theory and density functional theory. We find an excellent agreement between our theoretical results and previous experimental results [2,3]. We also discuss the microscopic mechanism of the P1-induced decoherence of the diamond NV center in detail. Our results provide a key reference, which can be employed to optimize the NV’s performance in various quantum applications such as NV-based magnetometry and NV-based quantum sensors. |
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