Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session W36: Novel Spin Qubit Materials and Technologies IFocus Recordings Available
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Sponsoring Units: DQI Chair: Alexandre Bourassa, Google Room: McCormick Place W-194A |
Thursday, March 17, 2022 3:00PM - 3:12PM |
W36.00001: Designing chromium(IV) molecular color centers Daniel W Laorenza, Arailym Kairalapova, Samuel L Bayliss, Tamar Goldzak, Samuel M Greene, Leah R Weiss, Pratiti Deb, Peter J Mintun, Kelsey A Collins, David D Awschalom, Timothy Berkelbach, Danna E Freedman Transition metal-based molecular spins are a promising class of chemically tunable quantum bits (qubits), providing precise control over both the physical and electronic structure within a scalable qubit platform. However, molecular systems typically lack an optically addressable ground state spin. To introduce this valuable resource into molecular spins, we recently created a series of chromium(IV) compounds with the desired optical-spin interface through bottom-up design [1]. Here, we illustrate the versatility of this methodology to generate designer molecular color centers by modifying the organic moieties, or ligands, directly bound to the chromium(IV) site. Variation of the surrounding ligands across six unique systems modulates both the optical emission and ground state zero-field splitting (ZFS) energies. Moreover, the small ZFS values allowed for coherent spin manipulation at X-band microwave frequency, enabling temperature, concentration, and orientation dependent investigations of the spin dynamics. Combining the experimental results with electronic structure calculations, we outline how to control the optical-spin interface in such Cr(IV) systems, laying the framework for directed design of structurally precise, optically addressable molecular qubits. |
Thursday, March 17, 2022 3:12PM - 3:24PM |
W36.00002: Room temperature spin coherence in defect-engineered monoisotopic hBN Andrew L Yeats, Evan R Glaser, Jiahan Li, Dylan Evans, Lianjie Xue, Song Liu, Bin Liu, James H Edgar, Ignas Lekavicius, Samuel G Carter, Joel Q Grim, Thomas L Reinecke Negatively charged boron vacancies in hBN have attracted attention for their optically addressable room temperature spin coherence, making them an attractive choice for quantum information and sensing applications in a 2D material platform. We present room temperature infrared photoluminescence (PL) and optically detected magnetic resonance (ODMR) experiments on hBN as a function of isotopic composition and varying doses of neutron irradiation. We also employ PL and ODMR microscopy at low temperature to characterize the spatial distribution of defects in these materials with an eye towards improving material properties for quantum information and sensing applications. |
Thursday, March 17, 2022 3:24PM - 3:36PM |
W36.00003: Tunable and Transferable Diamond Membranes for Integrated Quantum Technologies Xinghan Guo, Nazar Delegan, Jonathan C Karsch, Zixi Li, Tianle Liu, Robert T Shreiner, Amy Butcher, David D Awschalom, F. Joseph Heremans, Alexander A High Color centers in diamond are widely explored as qubits in quantum technologies. However, challenges remain in the effective and efficient integration of these diamond-hosted qubits in device heterostructures. Here, nanoscale-thick uniform diamond membranes are synthesized via ``smart-cut'' and isotopically (12C) purified overgrowth. These membranes have tunable thicknesses (demonstrated 50 nm to 250 nm), are deterministically transferable, have bilaterally atomically flat surfaces (≤0.3 nm), and bulk-diamond-like crystallinity. Color centers are synthesized via both implantation and in-situ overgrowth incorporation. Within 110 nm-thick membranes, individual germanium-vacancy (GeV-) centers exhibit stable photoluminescence at 5.4 K and average optical transition linewidths as low as 125 MHz. The room temperature spin coherence of individual nitrogen-vacancy (NV-) centers shows Ramsey spin dephasing times (T2*) and Hahn echo times (T2) as long as 150 μs and 400 μs, respectively. This platform enables the straightforward integration of diamond membranes that host coherent color centers into quantum technologies. |
Thursday, March 17, 2022 3:36PM - 4:12PM |
W36.00004: Enhancing spin coherence in optically addressable molecular qubits through host-matrix engineering Invited Speaker: Sam L Bayliss Molecular ‘color centers’ seek to combine key features of solid-state color centers–e.g., an optically addressable ground-state spin–with a versatile molecular architecture [1]. The modularity of molecular systems means these color centers can be ported across different environments e.g., host matrices, and engineering this environment enables qubit properties to be tuned. Here we demonstrate such environmental control with chromium(IV)-based molecular spins. Inserting these molecular color centers into a non-isostructural host matrix significantly enhances their spin coherence compared to using an isostructural host. This behavior results from the environment-induced breaking of the qubit’s symmetry, which generates a significant transverse zero-field splitting, creating transitions which are insensitive to magnetic-field noise. We model this behavior from first principles using cluster-correlation expansion methods, and further experimentally demonstrate enhanced optical contrast and spin-lattice relaxation times for host-matrix engineered molecular color centers. These results highlight the portability and environmental tunability of molecular color centers, indicating their promise for applications in quantum information science. |
Thursday, March 17, 2022 4:12PM - 4:24PM |
W36.00005: Comparison of dynamical decoupling applied to nitrogen-vacancy (NV) and substitutional nitrogen (P1) centers in diamond at 2.5 GHz Ethan Q Williams, Chandrasekhar Ramanathan Using inductively-detected pulsed ESR, we make stroboscopically observed ensemble measurements of both the nitrogen-vacancy (NV) and the substitutional nitrogen (P1) center under application of dynamical decoupling (DD) pulse sequences which effectively reduce noise and interactions that limit T2. We compare the effectiveness of various DD sequences for both defects in diamond samples containing either low (1 ppm) or high (100 ppm) P1 concentrations. At low P1 concentrations the low-frequency noise spectra are dominated by the carbon-13 nuclear spins. Since the resonant magnetic fields required for the NV (13 mT) and P1 (89 mT) centers are different in our fixed 2.5 GHz spectrometer, we are able to probe the field dependence of the nuclear spin noise. We also study NV-P1 interactions and the hyperpolarization of P1 centers. These results are significant for understanding the local magnetic noise environment in diamond-based sensors and for developing hyperpolarization strategies in diamond magnetometry. |
Thursday, March 17, 2022 4:24PM - 4:36PM |
W36.00006: Voltage-induced Modulation in the Charge State of Si-vacancy Defects in Diamond using High Voltage Nanosecond Pulses Stephen B Cronin Silicon-vacancy defects have been identified as a promising optical transition for quantum communications, quantum control, and quantum information processing. In the work presented here, we demonstrate a voltage-controlled mechanism by which the photoluminescent (PL) emission from silicon-vacancy (Si-V) defects in diamond can be modulated. In particular, we can selectively produce emission from the negatively charged state of this defect (i.e., Si-V–), which exhibits narrow (Γ = 4 nm) emission at 738 nm at low laser power. This approach uses high voltage (2-5kV) nanosecond pulses applied across top and bottom electrodes on a 0.5 mm thick diamond substrate. In the absence of high voltage pulses, we observe no emission at 738nm. This feature increases monotonically with peak pulse voltage, pulse repetition rate (i.e., frequency), and incident laser intensity. We observe saturation of the PL intensity for pulse voltages above 3.2 kV and frequency above 100 Hz. Based on electrostatic simulations, we estimated the local electric field intensity near the tip of the Cu electrode to be 2 x 105 V/cm at these voltages. However, as a function of laser power, we observe a linear dependence of PL intensity without saturation. These saturating and non-saturating behaviors provide important insight into the voltage-induce charging mechanisms and kinetics associated with this process. |
Thursday, March 17, 2022 4:36PM - 4:48PM |
W36.00007: Quantum spin-1 chain with NV centers in diamond: phase diagram and potential applications for quantum simulations Troy Losey, Jin Zhang, Denis R Candido, Yannick L Meurice, Michael E Flatté, Shan-Wen Tsai Quantum spin-1 chains have been studied extensively due to their rich phase diagram and potential applications as quantum simulators. The (1+1)-dimensional Abelian-Higgs model has been mapped, in a manifestly gauge-invariant way, to quantum spin-S Hamiltonians, and the effects of the S-truncation has been studied, with S=1 presenting particularly rich critical behavior [1]. Nitrogen-vacancy (NV) centers in diamond have spin triplet (S=1) states that can be initialized, and individually addressed and measured [2]. In addition, spin-spin interactions may be engineered through coupling to magnon modes [3,4]. Here we discuss potential applications of the NV centers in diamond as quantum simulators for universal critical behavior, and explore the phase diagram of one-dimensional NV-center spins coupled through magnetic dipole interaction. |
Thursday, March 17, 2022 4:48PM - 5:00PM |
W36.00008: Orders of magnitude improvement in coherence of silicon vacancy ensembles in isotopically purified 4H-SiC Ignas Lekavicius, Rachael L Myers-Ward, Daniel Pennachio, Jenifer Hajzus, Kurt Gaskill, Andrew Purdy, Andrew L Yeats, Peter G Brereton, Evan R Glaser, Thomas L Reinecke, Samuel G Carter The interaction of defects spins in semiconductors to their environment offers many sensing opportunities such as magnetic (ac and dc), strain and temperature measurements at ambient conditions. Magnetometers based on the nitrogen vacancy in diamond have already found applications ranging from sensing of biological and condensed matter systems. However, the difficulty of fabrication and price of diamond, as well as the introduction of substitutional nitrogen defects during the NV creation process has motivated exploration of alternative systems. Among these are silicon vacancy defects in silicon carbide, which have been shown to possess long lived spin coherence, spin initialization, and state readout at room temperature. However, the T2* of silicon vacancy ensembles (a critical parameter for sensing) has been limited to a few hundred nanoseconds, likely due to nuclear spins in the lattice. Here, we will present work using isotopic purification of the host crystal as well as a novel choice of basis which increases the T2* of the silicon vacancy ensemble to more than 20 microseconds. In this basis, the T2* has little dependence on defect density, showing promise for the use of the silicon vacancy as a high density, coherent defect ensemble for sensing. |
Thursday, March 17, 2022 5:00PM - 5:12PM |
W36.00009: Cavity Quantum Electrodynamics in Silicon Carbide Photonics with Color Centers Daniil M Lukin, Melissa A Guidry, Joshua Yang, Sattwik Mishra, Misagh Ghezellou, Hiroshi Abe, Takeshi Ohshima, Jawad Ul-Hassan, Jelena Vuckovic We demonstrate cavity quantum electrodynamics experiments with the silicon vacancy in 4H-Silicon-Carbide-on-Insulator integrated photonics. We show nearly-transform-limited, stable quantum emission from silicon vacancy defects in a microdisk resonator and observe emitter-cavity cooperativity approaching unity. We observe single- and two-photon interference between a pair of silicon vacancies, a prerequisite for multi-emitter quantum photonics in Silicon Carbide. |
Thursday, March 17, 2022 5:12PM - 5:24PM |
W36.00010: Coherent mechanical driving of chromium ion spins in commercial silicon carbide Berk D Kovos, Yeghishe Tsaturyan, Samuel J Whiteley, David D Awschalom Transition metal ions provide a rich set of defect-bound spin qubits in wide bandgap semiconductors with an optical interface and are promising candidates for hybrid quantum systems. For example, chromium in the 4+ charge state (Cr4+) in 4H silicon carbide (4H-SiC) produces a spin-1 ground state with T1 times longer than a second below 15 K and a spin-0 first excited state. Optical transitions between the two states form a Λ-like system, with spin selective optical transitions insensitive to strain. The ground state spins, however, are expected to be highly strain susceptible. To test this, we use a Cr implanted commercial 4H-SiC substrate, with a fabricated surface acoustic wave resonator. Despite the fact that the defects are only 100 nm below the highly processed sample surface, we observe narrow optical transitions, allowing for spin sublevel addressability. We use this interface to characterize coherent spin-phonon interactions within the device. Our results demonstrate the potential of transition metal ion based qubits for hybrid quantum architectures. |
Thursday, March 17, 2022 5:24PM - 5:36PM |
W36.00011: Ab-initio study of nickel defects in diamond acting as qubits Gergő Thiering, Adam Gali Nickel is a typical contaminant during HPHT and CVD diamond synthesis, that paved the way to observe various nickel related optical signals in diamond during the past decades. However, various assignments of optical signals to defect structures are only tentative assumptions. For example, the 1.4-eV optical center was originally attributed to positively charged interstitial Ni, but our very recent results indicate that it should be associated with the negatively charged nickel-vacancy defect which was falsely associated with the 1.72-eV (NE4) center. Our study resolves a few decades controversy by means of ab-initio DFT simulations to predict optical fine structures and vibronic sidebands, zero field splitting tensors and EPR g-tensors. Furthermore, qubit protocols (Λ-scheme) for the 1.4-eV center are proposed towards quantum technology applications. |
Thursday, March 17, 2022 5:36PM - 5:48PM |
W36.00012: Unexpected enhancement of quartet spin state relaxation in silicon carbide due to isotope purification Viktor Ivady, Oscar E Bulancea Lindvall, Tien Son Nguyen, Igor A Abrikosov Spin defects and nuclear spins are often the major sources of decoherence and spin relaxation of solid-state qubits formed by optically addressable point defect spins in semiconductors. Understanding these inherently many-body phenomena is of crucial importance for advancing entanglement-based applications in solids. In our recent work, we utilize state-of-the-art theoretical tools to investigate dipolar spin relaxation and decoherence of a quartet spin qubit system provided by the negatively charged silicon vacancy point defect in silicon carbide. In particular, we study spin flip-flops at the zero-field region, where the quartet states are only slightly split due to the marginal zero-field interaction, and quantify relevant decay times at increased magnetic field values for various spin-active defect concentrations and nuclear spin abundances. Furthermore, we demonstrate that isotope purification, which reduces nuclear spin induced decoherence and spin relaxation interactions, also enhances the coupling of the quartet spin with neighboring spin-1/2 point defects through the elimination of local inhomogeneity of the host. This magnetic field independent effect can limit both the T1 and the T2 time in an unexpected way in realistic materials. |
Thursday, March 17, 2022 5:48PM - 6:00PM |
W36.00013: Realisation of electron-spin-pair qubit in diamond Nicolas Demetriou Realizing quantum networks requires quantum registers next to optically addressable qubits. A variety of |
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