Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A28: Dopants and Defects in Semiconductors I: Quantum InformationFocus
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Sponsoring Units: DMP FIAP DCOMP GQI Chair: Paul Koenraad, Eindhoven University of Technology Room: 291 |
Monday, March 13, 2017 8:00AM - 8:36AM |
A28.00001: A photonic link for donor spin qubits in silicon Invited Speaker: Stephanie Simmons Atomically identical donor spin qubits in silicon offer excellent native quantum properties, which match or outperform many qubit rivals. To scale up such systems it would be advantageous to connect silicon donor spin qubits in a cavity-QED architecture. Many proposals in this direction introduce strong electric dipole interactions to the otherwise largely isolated spin qubit ground state in order to couple to superconducting cavities. Here I present an alternative approach, which uses the built-in strong electric dipole (optical) transitions of singly-ionized double donors in silicon. These donors, such as chalcogen donors S$+$, Se$+$ and Te$+$, have the same ground-state spin Hamiltonians as shallow donors yet offer mid-gap binding energies and mid-IR optical access to excited orbital states. This photonic link is spin-selective which could be harnessed to measure and couple donor qubits using photonic cavity-QED. This approach should be robust to device environments with variable strains and electric fields, and will allow for CMOS- compatible, bulk-like, spatially separated donor qubit placement, optical parity measurements, and 4.2K operation. I will present preliminary data in support of this approach, including 4.2K optical initialization/readout in Earth's magnetic field, where long T1 and T2 times have been measured. [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 8:48AM |
A28.00002: Towards single atom devices: weak localization in embedded phosphorus delta layers in silicon Joseph Hagmann, Xiqiao Wang, Pradeep Namboodiri, Jonathan Wyrick, Roy Murray, M. D. Stewart, Richard Silver, Curt Richter Key to the fabrication of devices based on the deterministic placement of dopants in silicon is the formation of phosphorus dopant monolayers and the overgrowth of high quality crystalline Si. Lithographically defined dopant delta-layers can be formed with a scanning tunnel microscope which can pattern device features on a hydrogen-terminated silicon surface by exposing Si dangling bonds at specific locations and implanting phosphorus at these locations with atomic precision. We describe advancements in the dopant formation and overgrowth processes necessary to produce prototypical few-atom devices in a controlled solid-state environment. The structure of the samples is determined from a suite of measurements that includes STM, TEM, and SIMS, and is directly correlated with the electrical properties measured by magnetotransport. We examine the effect of delta layer quality on the weak localization (WL) observed in these samples at low temperatures and low magnetic fields. We present parameters extracted from the fit of the WL feature to the Hikami-Larkin-Nagaoka equation that, alongside descriptions of delta-layer quality and dopant diffusion, demonstrate a method of testing these aspects of sample synthesis through electrical transport. [Preview Abstract] |
Monday, March 13, 2017 8:48AM - 9:00AM |
A28.00003: Optimizing the properties of defects at Si surfaces using quantum confinement and strain Peter Scherpelz, Giulia Galli By manipulating hydrogen-passivated silicon surfaces with an STM tip, dangling bonds (DBs) can be created, which behave as quantum dots with potential applications for quantum information technology. Here we use density functional and many-body perturbation theory calculations to study a single DB on Si(100), and demonstrate how the properties of DB states can be altered in order to design the behavior of DB quantum dots. We show that while in thick Si films the singly-occupied DB state is resonant with the bulk valence band, in quantum-confined thin films the state is an isolated impurity state in the band gap. We also find that strain can further isolate DBs in the gap of the material, depending on the sample geometry and morphology. Finally, we calculate charge transition levels and show how these also depend on the sample structural properties. These findings suggest new methods for tuning the properties of defects used in quantum information, and also inform on the parameters required to perform converged simulations of silicon surfaces. [Preview Abstract] |
Monday, March 13, 2017 9:00AM - 9:12AM |
A28.00004: Localization and Correlations in Chains of Donors in Si. Amintor Dusko do Amaral Oliveira, Alain Delgado, Andre Saraiva, Pawel Hawrylak, Belita Koiller Experiments on nanowires of donors in silicon (Si) show metal-insulator transition and ohmic conductance. The understanding of such properties is challenging in view of the expected localization of single-particle electronic states in imperfect 1D systems and many-body localization in strongly interacting 1D systems. We explore disordered nanostructures within a standard single electron approach. Many-body~effects are assessed by treating ordered chains. The electronic wavefunction in substitutional P donor nanowires in Si is given as a linear combination of dopant ground state orbitals. The electron-electron (e-e) interactions are included by extending the tunneling Hamiltonian into an extended Hubbard-Kanamori Hamiltonian (HKH). Besides the single particle parameters, on-site energy and nearest-neighbors hopping, the HKH model includes Hubbard (U) and nearest-neighbors direct (V) e-e terms. We compute U and V using the single electron orbitals. Except for U, all parameters depend on relative positions of donor pairs in Si lattice. In the non-interacting regime, disorder leads to electron localization quantified by the localization length. We study the impact of hopping and disorder on observed conductance and the effect of e-e interactions on real space correlations and on absorption of light. [Preview Abstract] |
Monday, March 13, 2017 9:12AM - 9:24AM |
A28.00005: A Well-Defined STM Image Resulting From Current-Induced Defect Fluctuations: The Butterfly On Si(001):H and Ge(001):H Daniel Sanchez-Portal, Mads Engelund, Thomas Frederiksen, Szymon Godlewski, Marek Kolmer, Rafal Zuzak, Bartosz Such, Marek Szymonski Dangling bond (DB) arrays on Si(001):H and Ge(001):H surfaces can be patterned with atomic precision and exhibit complex and rich physics. Scanning tunneling microscopy (STM) images of DB arrays are often difficult to interpret and simulate. Recently it was shown that low-temperature imaging of unoccupied states of an unpassivated dimer on Ge(001):H results in a symmetric ``butterfly''-like STM pattern, despite that the equilibrium dimer configuration is expected to be a bistable, buckled geometry. Here, based on a thorough characterization of the low-bias switching, we propose a new imaging model featuring a dynamical two-state rate equation.[1] On both Si(001):H and Ge(001):H, we can reproduce the observed features, which strongly corroborates that the patterns arise from fast switching events and provides insight into the relation between the tunneling current and switching rates. We envision that our imaging model can be applied to simulate other bistable systems. [1] M. Engelund et al., Phys. Chem. Chem. Phys. 18, 19309-17 (2016) doi: 10.1039/c6cp04031d. [Preview Abstract] |
Monday, March 13, 2017 9:24AM - 9:36AM |
A28.00006: Quantum point contacts for electrons on H-Si(111) surfaces using a Ga focused-ion beam for direct-write implant lithography Luke D. Robertson, B. E. Kane Quantum point contacts (QPCs) realized in materials with anisotropic electron mass, such as Si, may exhibit valley filter phenomena leading to extreme sensitivity to single donor occupancy, and thus are of interest to measurement schemes for donor-based quantum information processing. To this end, we have developed ambipolar devices on a H-Si(111):Si(100)/SiO$_{\mathrm{2}}$ flip-chip assembly which utilize in-plane, degenerately doped n$^{\mathrm{+}}$ (P) and p$^{\mathrm{+}}$ (B) contacts to probe transport in a 2D electron system (2DES). In addition to providing electrostatic isolation of carriers, these p-type contacts can be used as lateral depletion gates to modulate the 2DES conductance, and if extended to the nanoscale can lead to 1D confinement and quantized conductance of the 2DES. In this talk, I will describe our efforts to use a Ga focused-ion beam for direct-write implant lithography to pattern QPCs and Ga nanowires on H-Si(111) surfaces. I will present low temperature (4.2K) conductance data collected on 30nm Ga nanowires to demonstrate their effectiveness as lateral depletion gates, and discuss on going measurements to confine and modulate the conductance of the 2DES using Ga QPCs. [Preview Abstract] |
Monday, March 13, 2017 9:36AM - 9:48AM |
A28.00007: Abstract Withdrawn
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Monday, March 13, 2017 9:48AM - 10:00AM |
A28.00008: Ab initio theory of spin-orbit coupling for quantum bits in diamond exhibiting dynamic Jahn-Teller effect Adam Gali, Gerg\H{o} Thiering Dopants in solids are promising candidates for implementations of quantum bits for quantum computing. In particular, the high-spin negatively charged nitrogen-vacancy defect (NV) in diamond has become a leading contender in solid-state quantum information processing. The initialization and readout of the spin is based on the spin-selective decay of the photo-excited electron to the ground state which is mediated by spin-orbit coupling between excited states states and phonons. Generally, the spin-orbit coupling plays a crucial role in the optical spinpolarization and readout of NV quantum bit (qubit) and alike. Strong electron-phonon coupling in dynamic Jahn-Teller (DJT) systems can substantially influence the effective strength of spin-orbit coupling. Here we show by ab initio supercell density functional theory (DFT) calculations that the intrinsic spin-orbit coupling is strongly damped by DJT effect in the triplet excited state that has a consequence on the rate of non-radiative decay. This theory is applied to the ground state of silicon-vacancy (SiV) and germanium-vacancy (GeV) centers in their negatively charged state that can also act like qubits. We show that the intrinsic spin-orbit coupling in SiV and GeV centers is in the 100 GHz region, in contrast to the NV center of 10 GHz region. Our results provide deep insight in the nature of SiV and GeV qubits in diamond. [Preview Abstract] |
Monday, March 13, 2017 10:00AM - 10:12AM |
A28.00009: High-frequency EPR of surface impurities on nanodiamond Zaili Peng, Viktor Stepanov, Susumu Takahashi Diamond is a fascinating material, hosting nitrogen-vacancy (NV) defect centers with unique magnetic and optical properties. There have been many reports that suggest the existence of paramagnetic impurities near surface of various kinds of diamonds. Electron paramagnetic resonance (EPR) investigation of mechanically crushed nanodiamonds (NDs) as well as detonation NDs revealed g$\sim$2 like signals that are attributed to structural defects and dangling bonds near the diamond surface. In this presentation, we investigate paramagnetic impurities in various sizes of NDs using high-frequency (HF) continuous wave (cw) and pulsed EPR spectroscopy [1]. Strong size dependence on the linewidth of HF cw EPR spectra reveals the existence of paramagnetic impurities in the vicinity of the diamond surface. We also study the size dependence of the spin-lattice and spin-spin relaxation times ($T_1$ and $T_2$) of single substitutional nitrogen defects in NDs Significant deviations from the temperature dependence of the phonon-assisted $T_1$ process were observed in the ND samples, and were attributed to the contribution from the surface impurities. [1] F. H. Cho, V. Stepanov, R. D. Akiel, X. Zhang, and S. Takahashi, submitted (2016). [Preview Abstract] |
Monday, March 13, 2017 10:12AM - 10:24AM |
A28.00010: Polarization and Optically Detected Magnetic Resonance of P1 Centers in Diamond Eric Kamp, Brian Carvajal, Nitin Samarth To achieve the highest magnetic field sensitivity, sensors for nitrogen vacancy (NV) center magnetometry require high densities of NV centers. In these sensors, the electron spin of the substitutional nitrogen (P1) center is the primary cause of decoherence. One route to eliminate this decoherence is to polarize the P1 centers. We demonstrate a simple technique for transferring optically induced polarization in the NV center onto the P1 center, relying on simultaneous driving of the mutual spin flip transitions within the NV-P1 center system and optical pumping of the NV center. By modeling the density operators for this system, we show that due to the large optically induced spin polarization of the NV center, this process generates large enhancements in the P1 center spin polarization. To corroborate our models, we compared them with optically detected magnetic resonance (ODMR) signals generated by the mutual spin flip transitions at zero field. Further, we show that the generated polarization enables ODMR measurements of the P1 center, conditional on the driving of mutual spin flip transitions. This technique should enable polarization of the electronic component of the P1 center and prolong coherence times of high-density NV center ensembles at room temperature. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 10:36AM |
A28.00011: Efficient coherent driving of NV centers in a YIG-nanodiamond hybrid platform Paolo Andrich, Charles F. de las Casas, Xiaoying Liu, Hope L. Bretscher, Paul F. Nealey, David D. Awschalom, F. Joseph Heremans The nitrogen-vacancy (NV) center in diamond is an ideal candidate for room temperature quantum computing and sensing applications. These schemes rely on magnetic dipolar interactions between the NV centers and other paramagnetic centers, imposing a stringent limit on the spin-to-spin separation. For instance, creating multi-qubit entanglement requires two NV centers to be within a few nanometers of each other, limiting the possibility for individual optical and microwave (MW) control. Moreover, to sense spins external to the diamond lattice the NV centers need to be within few nanometers from the surface, where their coherence properties are strongly reduced. In this work, we address these limitations using a hybrid YIG-nanodiamond platform where propagating spin-waves (SWs) are used to mediate the interaction between a MW source and a NV center ensemble, thereby relaxing the requirements imposed by dipolar interactions. In particular, we show that SWs can be used to amplify a MW signal detected by the NV centers by more than two orders of magnitude, allowing us to obtain ultra-low energy SW-driven coherent control of the NV centers. These results demonstrate the potentials of YIG-ND hybrid systems for the realization of enhanced quantum sensing and scalable computing devices. [Preview Abstract] |
Monday, March 13, 2017 10:36AM - 10:48AM |
A28.00012: Tunneling barrier height spectroscopy with single-electron tunneling events K Ambal, C .C. Williams, C Boehme The energy of individual localized defect states in dielectric films has been measured by Dynamic Tunneling Force Microscopy [1]. Here, the tunneling dynamics of single electrons from a Fermi reservoir to these localized defect states in a silicon dioxide thin-film at 77K is studied using quartz tuning-fork based force detection with a Pt scanning-probe tip. When the tip-Fermi energy is aligned to a localized defect state, random tunneling of individual electrons between state and tip occurs, causing cantilever-detected electrostatic forces to exhibit random telegraph noise. The tunneling rate dependence on the tip-sample gap determines the local tunneling barrier height. The experiments demonstrate single-electron tunneling barrier height spectroscopy of individual defect states and suggest their applicability for tunneling based single-spin detection [2]. [1] Wang et al, Appl. Phys. Lett. 105, 052903 (2014) [2] Payne et al, Phys. Rev. B 91, 195433 (2015). [Preview Abstract] |
Monday, March 13, 2017 10:48AM - 11:00AM |
A28.00013: Electronic and Structural Symmetry of Quantum Emitters in Hexagonal Boron Nitride Annemarie Exarhos, David Hopper, Richard Grote, Jennifer Saouaf, Audrius Alkauskas, Lee Bassett Analogous to three-dimensional wide-bandgap semiconductors like diamond and silicon carbide, hexagonal boron nitride (h-BN) hosts isolated defects exhibiting single-photon emission at room temperature. The ability to create quantum emitters within a two-dimensional material promises breakthrough advances in quantum sensing, photonics, and use in multi-functional heterostructures. Critical to such applications, however, is an understanding of the physics underlying h-BN's quantum emission. Here, we characterize the angular dependence of h-BN defect fluorescence as a function of excitation polarization. Using single-crystal exfoliated h-BN films treated to create quantum emitters, we study correlations between the defect dipole orientation and the h-BN crystallographic axes with fluorescence spectroscopy and electron backscatter diffraction. Initial studies indicate a weak correlation of the absorptive dipole with the h-BN lattice, although some dipoles are notably uncorrelated with the lattice (Exarhos \textit{et al.}, arXiv:1609.02641 (2016)). Additionally, grain boundaries and local lattice strain may play a role in the absorptive dipole orientation. [Preview Abstract] |
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