Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session Y5: Semiconductor Spin QubitsFocus
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Sponsoring Units: GMAG DMP FIAP Chair: Igor Zutic, University at Buffalo Room: 301 |
Friday, March 18, 2016 11:15AM - 11:27AM |
Y5.00001: Microscopic origin of the prolonged coherence in 4H-SiC divacancy spin qubits Hosung Seo, Abram Falk, Paul Klimov, David Christle, David Awschalom, Giulia Galli Long coherence times of quantum bits (qubits) is a key prerequisite for quantum computing and quantum metrology. Recently, electronic spin qubits localized to divacancies in 4H-SiC were found to have a long spin coherence time (T2) exceeding 1 ms, which is longer than that of the nitrogen-vacancy (NV) center in chemically but not isotopically purified diamond. In this talk, we discuss the microscopic origin behind the prolonged divacancy coherence. By using optically detected magnetic resonance (ODMR), we show that the divacancy T2 rapidly increases as a function of magnetic field, saturating at 1.3 ms at T $=$ 20 K. We used a quantum-bath model combined with a cluster correlation expansion technique to calculate the divacancy coherence function and found an excellent agreement between theory and experiment. We show that an effective decoupling of the 29Si and 13C nuclear spins due to their gyromagnetic ratio difference is one of the key reasons responsible for suppressing the decoherence of the divacancy qubits in SiC under magnetic fields larger than 100G. [Preview Abstract] |
Friday, March 18, 2016 11:27AM - 11:39AM |
Y5.00002: Coherent population trapping of a nitrogen vacancy center induced by optical and surface acoustic waves Thein Oo, Andrew Golter, Hailin Wang We report experimental demonstration of coherent population trapping (CPT) driven by resonant optical and mechanical coupling in a nitrogen vacancy (NV) center in diamond. A surface acoustic wave (SAW) is generated with an inter-digital transducer fabricated on a ZnO layer sputtered on diamond surface. The SAW couples resonantly to a transition between two excited states of the NV center, while a laser field couples to a corresponding resonant optical transition. The combined optical and mechanical coupling to the lamda- or ladder- type three-level system leads to CPT of the NV center. These studies open the door to exploiting strong excited-state electron-phonon coupling for applications such as laser cooling of a mechanical resonator and mechanically-mediated spin entanglement. [Preview Abstract] |
Friday, March 18, 2016 11:39AM - 11:51AM |
Y5.00003: Quantum Control of a Nitrogen-Vacancy Center using Surface Acoustic Waves in the Resolved Sideband Limit David Golter, Thein Oo, Maira Amezcua, Hailin Wang Micro-electromechanical systems research is producing increasingly sophisticated tools for nanophononic applications. Such technology is well-suited for achieving chip-based, integrated acoustic control of solid-state quantum systems. We demonstrate such acoustic control in an important solid-state qubit, the diamond nitrogen-vacancy (NV) center. Using an interdigitated transducer to generate a surface acoustic wave (SAW) field in a bulk diamond, we observe phonon-assisted sidebands in the optical excitation spectrum of a single NV center. This exploits the strong strain sensitivity of the NV excited states. The mechanical frequencies far exceed the relevant optical linewidths, reaching the resolved-sideband regime. This enables us to use the SAW field for driving Rabi oscillations on the phonon-assisted optical transition. These results stimulate the further integration of SAW-based technologies with the NV center system. [Preview Abstract] |
Friday, March 18, 2016 11:51AM - 12:03PM |
Y5.00004: Development of single-crystal diamond scanning probes with nitrogen-vacancy centers for cryogenic magnetometry with nanoscale spatial resolution Alec Jenkins, Matthew Pelliccione, Preeti Ovartchaiyapong, Christopher Reetz, Ania Bleszynski Jayich Scanning probes based on the nitrogen-vacancy (NV) defect center in diamond are powerful tools for imaging magnetic phenomena at the nanoscale. In particular, extending the operation of these probes to cryogenic temperatures opens up a wide range of condensed matter systems that can be studied. In this talk, we demonstrate a variable temperature NV scanning magnetometer consisting of an atomic-force microscope housed in a closed-cycle cryostat integrated with custom confocal optics. With this microscope we have observed 6-nm spatial resolution and 3 $\mu$T/$\sqrt{\mbox{Hz}}}$ sensitivity at $T$ = 6 K. The single-crystal diamond scanning probes that contain shallow and coherent NV centers are critical to the performance of the microscope. The probes are designed with the aim of reducing the NV-sample separation and increasing collection of NV fluorescence, both while maintaining the spin coherence properties of the defects. We describe the fabrication of these probes as well as ongoing efforts to improve their sensitivity and spatial resolution. [Preview Abstract] |
Friday, March 18, 2016 12:03PM - 12:15PM |
Y5.00005: Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor Matthew Pelliccione, Alec Jenkins, Preeti Ovartchaiyapong, Christopher Reetz, Eve Emmanuelidu, Ni Ni, Ania Bleszynski Jayich The nitrogen vacancy (NV) defect in diamond has emerged as a promising candidate for high resolution magnetic imaging based on its atomic size and quantum-limited sensing capabilities afforded by long spin coherence times. Although the NV center has been successfully implemented as a nanoscale scanning magnetic probe at room temperature, it has remained an outstanding challenge to extend this capability to cryogenic temperatures, where many solid-state systems exhibit non-trivial magnetic order. In this talk, we present NV magnetic imaging at $T$ = 6 K, first benchmarking the technique with a magnetic hard disk sample, then utilizing the technique to image vortices in the iron pnictide superconductor BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$ with $T_c$ = 30 K. In addition, we discuss other candidate solid-state systems that can benefit from the high spatial resolution and field sensitivity of the scanning NV magnetometer. [Preview Abstract] |
Friday, March 18, 2016 12:15PM - 12:27PM |
Y5.00006: Coupling a driven magnetic vortex to individual nitrogen-vacancy spins for fast, nanoscale addressability and coherent manipulation Michael Wolf, Robert Badea, Jesse Berezovsky The core of a ferromagnetic (FM) vortex domain creates a strong, localized magnetic field which can be manipulated on nanosecond timescales using small magnetic fields, or electrical currents. These capabilities present opportunities for nanoscale spin-based devices. Here, we demonstrate how these FM vortex properties can be used in a room temperature, integrated device by coupling a FM vortex to nitrogen-vacancy (NV) center spins in diamond [1]. Measurements are carried out using a combined magneto-optical microscopy and optically-detected spin resonance technique. We show that the FM vortex can be driven into proximity with an NV, inducing significant NV spin splitting and sufficiently large magnetic field gradient to address spins separated by nanometer length scales. By applying a microwave-frequency magnetic field, we drive both the vortex and the NV spins, resulting in enhanced coherent rotation of the spin state. Finally we demonstrate that by driving the vortex on fast timescales, sequential addressing and coherent manipulation of spins is possible on ~100 ns timescales, while driving on faster timescales results in non-trivial coherent dynamics of the coupled vortex/NV system. [1] Wolf, M.S., Badea, R., and Berezovsky, J., cond-mat/1510.07073, (2015) [Preview Abstract] |
Friday, March 18, 2016 12:27PM - 12:39PM |
Y5.00007: Navigating the vortex pinning landscape for bistable coupling of a ferromagnetic vortex to individual nitrogen vacancy spins Jesse Berezovsky, Michael Wolf, Robert Badea A ferromagnetic (FM) vortex coupled to nitrogen-vacancy (NV) spins in diamond provides an integrated platform for fast, nanoscale addressability of coherent spins [1]. The vortex moves in a complex effective potential landscape set by the geometry of the disk and the defects present in the material. As the vortex moves through this landscape, the coupling to a proximal NV varies. We use differential magneto-optical microscopy to extract the effective potential through which the vortex moves [2], and optically-detected magnetic resonance to study the coupling of the vortex to an adjacent NV spin. When multiple local minima are present in the vortex potential, the vortex/NV coupling displays bistability. We switch between these bistable states with short magnetic field pulses. This allows an NV spin transition to be switched between on-resonance and off-resonance with a driving field with the same set of external parameters, and also yields information about the mechanisms of vortex/NV coupling. [1] M.S. Wolf, R. Badea, J. Berezovsky, arXiv:1510.07073, 2015 [2] R. Badea, J. Berezovsky, arXiv:1510.07059, 2015. [Preview Abstract] |
Friday, March 18, 2016 12:39PM - 12:51PM |
Y5.00008: Phonon induced two-electron relaxation in two donor qubits in silicon Yuling Hsueh, Archana Tankasala, Yu Wang, Gerhard Klimeck, Michelle Simmons, Rajib Rahman An atomistic method of calculating two-electron spin-lattice relaxation times (T$_{\mathrm{1}})$ is presented for two donor qubits in silicon. The singlet-triplet two-electron states are calculated from full-configuration interaction (FCI) method with one-electron basis states obtained from the tight-binding Hamiltonian including spin-orbit interaction. The FCI solution enables the investigation of various regimes of donor separations, including very closely separated donor pairs in which rearrangement of excited bonding and anti-bonding states change the wavefunction symmetries. Hyperfine mixing from the nuclear spins is included perturbatively into the two-electron states. To calculate the T$_{\mathrm{1\thinspace }}$times, the electron-phonon Hamiltonian is evaluated from the strain-dependent tight-binding Hamiltonian. The results show how the T$_{\mathrm{1}}$ times in donor qubits vary with magnetic field and donor separation for each of the three triplets. Moreover, the variation of T$_{\mathrm{1}}$ with the electric field controlled exchange coupling is also investigated. [Preview Abstract] |
Friday, March 18, 2016 12:51PM - 1:03PM |
Y5.00009: Pauli spin blockade in CMOS silicon double dots probed by dual gate reflectometry Dharmraj Kotekar Patil, Alessandro Crippa, Romain Maurand, Andrea Corna, Romain Lavieville, Louis Hutin, Sylvain Barraud, Alexei Orlov, Silvano De Franceschi, Marc Sanquer, Xavier Jehl Silicon quantum dots are attractive candidates for the development of scalable spin-based qubits. The Pauli spin blockade effect in double quantum dots can provide an efficient, temperature-independent mechanism for qubit readout. Here we report the observation of Pauli blockade in silicon double quantum dots defined in double-gate nanowire transistors fabricated using silicon-on-insulator CMOS technology. Each of the two gates is connected to an LC resonator to perform radio-frequency reflectometry. This powerful technique allows high-sensitivity detection of charge transitions in the double quantum dot down to the few-electron regime. We find evidence of Pauli spin blockade and study the magnetic-field dependence of the underlying singlet-triplet states. [Preview Abstract] |
Friday, March 18, 2016 1:03PM - 1:15PM |
Y5.00010: Spin Exchange oscillations between distant quantum dots Takafumi Fujita, Tim Baart, Christian Reichl, Werner Wegscheider, Lieven Vandersypen Interactions mediated by long-range quantum coherence lie at the heart of important phenomena in many different fields. Charge transfer during oxidative stress in DNA [1], reactions in photosynthetic molecules [2], and behaviour of cuprate superconductors [3] are all described by tunnelling via virtual hopping. Such mechanism may also provide new ways of using quantum dots for fault tolerant quantum information processing [4]. In the presence of long-range tunnel coupling mediated by virtual occupation of intermediate levels, superexchange interactions can induce coherent oscillations between two distant electron spins. We implement this scheme in a linear array of three quantum dots with one electron on each of the outer dots. We observe coherent exchange oscillations between the two spins, and the oscillation frequency is controlled by the detuning of the electrochemical potential of the dot in between. Spin exchange at a distance may provide a new route for scaling up electron spin qubits using quantum dots. [1] B. Giese, et al, Nature 412, 318-320 (2001). [2] X.F. Wang, et al, Phys. Rev. Lett. 97,106602 (2006). [3] C. Kim, et al, Phys. Rev. Lett. 80, 4245 (1998). [4] F. Braakman, et al, Nature Nano. 8, 432-437 (2013). [Preview Abstract] |
Friday, March 18, 2016 1:15PM - 1:27PM |
Y5.00011: Decoherence of an electron spin qubit in an optically active quantum dot Fuxiang Li, Alexander Bechtold, Dominik Rauch, Tobias Simmet, Per-Lennart Ardelt, Armin Regler, Kai Mu¨ller, Nikolai Sinitsyn, Jonathan Finley Understanding the spin dynamics in quantum dot, especially its detailed decoherence and relaxation is not only of theoretical interests, but also a crucial problem towards the application of quantum dot as a solid-state quantum qubit. From the phenomenological models of decoherence developed more than a decade ago, it has been now fairly accepted that the spin dynamics undergoes two stages, first a fast ensemble dephasing due to the coherent precession of spin qubit around nearly static but randomly distributed hyperfine fields (~ 2 ns) and then a much slower relaxation process ($> 1 \mu$ s) due to dynamics of the nuclear spin bath induced by complex many-body interaction effects. However, this characteristics has never been verified in the experiment, until the recent experiment breakthrough I'm going to talk about. What’s more interesting is that, the experiment unambiguously shows a more complex picture, in which two dips rather than one, develops, which can be attributed to the effect of the comparatively strong quadruple field. [Preview Abstract] |
Friday, March 18, 2016 1:27PM - 1:39PM |
Y5.00012: Coherent control of single spins in a silicon carbide pn junction device at room temperature Sang-Yun Lee, Matthias Widmann, Ian Booker, Matthias Niethammer, Takeshi Ohshima, Adam Gali, Nguyen T. Son, Erik Janz\'{e}n, Joerg Wrachtrup Spins in single defects have been studied for quantum information science and quantum metrology. It has been proven that spins of the single nitrogen-vacancy (NV) centers in diamond can be used as a quantum bit, and a single spin sensor operating at ambient conditions. Recently, there has been a growing interest in a new material in which color centers similar to NV centers can be created and whose electrical properties can also be well controlled, thus existing electronic devices can easily be adapted as a platform for quantum applications. We recently reported that single spins of negatively charged silicon vacancies in SiC can be coherently controlled and long-lived at room temperature\footnote{M. Widmann, et al., Nat Mater 14, 164 (2015)}. As a next step, we isolated single silicon vacancies in a SiC pn junction device and investigated how the change in Fermi level, induced by applying bias, alters the charge state of silicon vacancies, thus affects the spin state control. This study will allow us to envision quantum applications based on single defects incorporated in modern electronic devices. [Preview Abstract] |
Friday, March 18, 2016 1:39PM - 1:51PM |
Y5.00013: Optical and Spin Signatures of Transition Metal Impurities in Silicon Carbide William Koehl, Samuel J. Whitely, Berk Diler, Alexandre Bourassa, David D. Awschalom, Nguyen Tien Son Point defects and impurities are increasingly viewed as an important resource for solid-state implementations of quantum information technologies. Electronic spins bound to point defects like the nitrogen vacancy center in diamond and divacancy in silicon carbide are especially attractive because they function as long-lived qubit states that can be controlled optically at the single-site level. These capabilities have generated a growing interest in identifying other classes of point defect with similar properties, since discovery of such systems might allow for new ranges of functionality in solid-state quantum device design. Transition metal ions are a promising area for exploration, since they often introduce isolated electronic levels within the bandgaps of semiconductors and possess a wide variety of magnetic and optical properties. Here we describe recent experimental studies of the optical and spin properties of transition metal impurities in silicon carbide. Using ensemble spectroscopies, we evaluate their potential for use as optically-controllable spin states within this industrially-important, wide-bandgap, optoelectronic material. [Preview Abstract] |
Friday, March 18, 2016 1:51PM - 2:03PM |
Y5.00014: Measurement of Spin Coherence Times in Proton Irradiated 4H-SiC Jacob Embley, John Colton, Sam Carter, Kyle Miller, Margaret Morris Silicon vacancy defects in silicon carbide (SiC) have potential for use in spintronic devices. We used optically detected magnetic resonance and a spin echo technique to measure T$_{\mathrm{2}}$ spin coherence times for electrons in 4H-SiC. These experiments were performed at a magnetic field strength of 0.371 T and a resonant microwave frequency of 10.5 GHz. Each sample contained silicon vacancy defects that were formed through irradiation with 2 MeV protons at unique fluences (10$^{\mathrm{13}}$ and 10$^{\mathrm{14}}$ cm$^{\mathrm{-2}})$. Measurements for each sample were made across a range of temperatures, from 8 K to room temperature. While we generally observed a decrease in spin coherence time with temperature, we also observed a range of temperatures (from 60 K to 160 K) for which the overall trend was reversed. [Preview Abstract] |
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