Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session M29: Semiconductor Qubits - Novel Spin Qubit Materials and Technologies IFocus Live
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Sponsoring Units: DQI Chair: Daniel Keith |
Wednesday, March 17, 2021 11:30AM - 11:42AM Live |
M29.00001: Kramers doublet transition metal point defects in hexagonal silicon carbide András Csóré, Adam Gali Transition metal (TM) point defects in silicon carbide (SiC) have attracted special attention recently owing to their highly promising properties with respect to quantum technology applications. Paramagnetic electronic structure of these defects exhibits a rich set of interesting and not yet fully resolved physics. A complex interplay between the electronic orbitals, phonons and electron spin determines the effective pseudospin of the system that we demonstrate on vanadium and molybdenum defects in hexagonal SiC by means of ab initio calculations [1]. Furthermore, we show that this interaction leads to the giant anisotropy in the g-tensor of the TM defects with Kramers doublet spin ground state, resulting in reduced and vanishing interaction with the magnetic field in parallel and transverse directions, respectively. The consequences of our finding in the application of these defects for quantum information processing will be discussed [1]. [1] A. Csóré, A. Gali, arXiv:1909.11587v2 |
Wednesday, March 17, 2021 11:42AM - 11:54AM Live |
M29.00002: Probing the coherence of solid-state qubits at avoided crossings Mykyta Onizhuk, Kevin Miao, Joseph Blanton, He Ma, Christopher Anderson, Alexandre Bourassa, David Awschalom, Giulia Galli The avoided crossing of energy levels in spin defects can be both beneficial and detrimental to quantum information applications. The emergence of a clock transition enhances the protection from magnetic noise thus improving coherence times, while ground state level anti-crossings (GSLAC) can increase longitudinal relaxation rates. We investigate the dynamics of divacancy spin qubits in SiC at a clock transition and near the GSLAC using a combination of theory and experiments. We present a theoretical approach based on a generalization of the cluster expansion method. We characterize the decoherence mechanism of spin qubits at avoided crossings, the transition from quantum to classical noise, and the emergence of multiple clock transitions arising from strongly coupled nuclear spins. Combined with ab-initio predictions of spin Hamiltonian parameters, the proposed theoretical approach paves the way to designing the coherence properties of spin qubits from first principles. [1,2] |
Wednesday, March 17, 2021 11:54AM - 12:06PM Live |
M29.00003: Stabilization of a solid-state spin qubit in a decoherence-protected subspace Joseph Blanton, Kevin Miao, Christopher Anderson, Alexandre Bourassa, Alexander Crook, Gary Wolfowicz, Hiroshi Abe, Takeshi Ohshima, David Awschalom Basal divacancies in silicon carbide (SiC) are solid-state spin systems with excellent spin coherence properties due to a clock transition at zero magnetic field [1,2]. When embedded in a decoherence-protected subspace (DPS) using a microwave dressing drive, the spin becomes highly insensitive to magnetic and electric fluctuations caused by impurities in the surrounding SiC lattice, resulting in record-long spin dephasing times greater than 22 ms [2]. Operation at the zero-field condition is accomplished using vector-magnetic control of the local field guided by analytical models of the DPS ground-state energy levels. Ramsey spectroscopy within the DPS is used to perform feedback that negates the effects of hertz-level shifts to the DPS energy levels that would otherwise introduce spurious dephasing. This demonstration of the coherence measurement of an electron spin qubit in a DPS indicates that utilizing this technique could lead to similar improvements in other systems where long coherence times and fast control are needed. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M29.00004: Improved ensemble spin coherence of silicon vacancies using isotopically purified 4H-SiC Samuel Carter, Rachael L Myers-Ward, Daniel J Pennachio, Jenifer R Hajzus, David Kurt Gaskill, Andrew P Purdy, Andrew L Yeats, Peter Brereton, Evan Richard Glaser, Thomas L Reinecke The silicon vacancy (VSi) in SiC is a promising defect for quantum information science and technology. In particular, the V2 VSi is one of the few defects with long-lived spin memory at room temperature and in a host material having a low abundance of nuclear spins. The 4.7% abundance of 29Si and 1.1% abundance of 13C, however, do have a significant effect on the spin coherence of VSi, resulting in hyperfine-induced side peaks in the spin transitions and strong echo modulation effects that limit the spin echo decay time for low magnetic fields (< ~10 mT) to less than 10 μs. Here, we report on ensemble spin coherence measurements of the V2 VSi for isotopically purified 4H-SiC epilayers, with much lower concentrations of 29Si and 13C. With room temperature optically detected magnetic resonance, we show very sharp ensemble transition linewidths down to 0.25 MHz and a T2* of up to 5 μs. Spin echo measurements show no sign of echo modulation from nuclear spins, giving an echo decay time of about 100 μs at a low magnetic field of 0.3 mT. We have also measured the effects of defect density and magnetic field on spin coherence. |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M29.00005: Single artificial atoms in silicon emitting at telecom wavelengths Alrik Durand, Walid Redjem, Tobias Herzig, Abdennacer Benali, Sebastien Pezzagna, Jan Meijer, Andrej Kuznetsov, Hai Son Nguyen, Sebastien Cueff, Jean-Michel Gerard, Isabelle Robert-Philip, Bernard Gil, Damien Caliste, Pascal Pochet, Marco Abbarchi, Vincent Jacques, Anaïs Dréau, Guillaume Cassabois
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Wednesday, March 17, 2021 12:30PM - 12:42PM Live |
M29.00006: Applications of a hole spin qubit with spin-orbit switch Florian Froning, Orson van der Molen, Leon Camenzind, Ang Li, Erik P. A. M. Bakkers, Dominik Zumbuhl, Floris Braakman Hole spins in Ge/Si nanowires feature a spin-orbit interaction that is both strong and gate-tunable [1,2]. Recently, this has led to the demonstration of a spin-orbit switch, which enables toggling a spin qubit between a fast control mode and a more coherent idling mode. The spin-orbit switch features a large electrical tunability of the Landé g-factor, which is of interest for individual qubit addressability in scaled up quantum circuits. |
Wednesday, March 17, 2021 12:42PM - 12:54PM Live |
M29.00007: Suppression of the optical linewidth and spin decoherence of a quantum spin center in a p–n diode Denis R Candido, Michael Flatté We present a quantitative theory of the suppression of the optical linewidth due to charge fluctuation noise in a p–n diode [1], recently observed in Ref. 2. We connect the local electric field with the voltage across the diode, allowing for the identification of the defect depth from the experimental threshold voltage. Furthermore, we show that an accurate description of the decoherence of such spin centers requires a complete spin–1 formalism that yields a bi-exponential decoherence process, and predict how reduced charge fluctuation noise suppresses the spin center's decoherence rate. |
Wednesday, March 17, 2021 12:54PM - 1:06PM Live |
M29.00008: Ultrafast hole spin qubit with spin-orbit switch Florian Froning, Leon Camenzind, Orson van der Molen, Ang Li, Erik P. A. M. Bakkers, Dominik Zumbuhl, Floris Braakman Hole spins in Ge/Si core/shell nanowires hold great promise as spin qubits with all-electrical control, taking advantage of the very strong direct Rashba spin-orbit interaction (SOI) for ultrafast electric dipole spin resonance. This SOI arises from the strong 1D confinement in the nanowire and provides full electrical control over its strength, thus making possible the implementation of a spin-orbit switch. Such switch allows to toggle the SOI-strength between a 'Control' state, with strong SOI for fast qubit operations, and an 'Idle' state, with weaker SOI for increased qubit lifetime. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M29.00009: Vanadium spin qubits as telecom quantum emitters in silicon carbide Gary Wolfowicz, Christopher Anderson, Berk Diler Kovos, Oleg Poluektov, F. Joseph, David Awschalom Solid state quantum emitters with addressable spin registers are promising platforms for quantum communication, yet few emit in the telecom band necessary for low-loss fiber networks. Here we create and isolate single vanadium dopants in silicon carbide (SiC) with emission in the O-band (~1300 nm) and with brightness allowing cavity-free detection, in a wafer scale CMOS-compatible material [1]. We demonstrate that their emission is stable and narrow near surfaces, enabling integration with nanoscale devices. |
Wednesday, March 17, 2021 1:18PM - 1:54PM Live |
M29.00010: Universal coherence protection and electrical control of spins in silicon carbide Invited Speaker: Kevin Miao Recent advances in material quality have led to the isolation of single optically active divacancy (VV) spin qubits in commercially available silicon carbide (SiC) wafers [1-3]. In particular, basally oriented VVs exhibit excellent spin and optical properties when operated near zero magnetic field. We isolate single kh basal VVs in 4H-SiC, where we demonstrate inhomogeneous spin dephasing times approaching 200 µs and Hahn-echo coherence times >1 ms. We map the excited-state fine structure of the kh VV and find near-transform-limited optical coherence in both time and frequency domains. The high degree of optical coherence allows us to implement gigahertz-frequency light-matter interactions, resulting in electrically controlled Landau-Zener-Stückelberg interferometry with the VV orbital levels [1]. |
Wednesday, March 17, 2021 1:54PM - 2:06PM Live |
M29.00011: Purcell enhancement of a silicon carbide color center with coherent spin control Alexander Crook, Christopher Anderson, Kevin Miao, Alexandre Bourassa, Hope Lee, Sam L Bayliss, David O Bracher, Xingyu Zhang, Hiroshi Abe, Takeshi Ohshima, Evelyn L Hu, David Awschalom Silicon carbide (SiC) has recently been developed as a platform for optically addressable spin defects such as the neutral divacancy, most notably in the 4H polytype. Here we present the Purcell enhancement and coherent spin control of a single divacancy coupled to a photonic crystal cavity [1]. We combine nanolithographic techniques with a dopant-selective photoelectrochemical etch to produce a suspended SiC nanobeam cavity with a quality factor of ~5000. This results in a Purcell factor of ~50 for a divacancy within the cavity mode, which increases photoluminescence into the zero-phonon line and shortens the excited state lifetime. Additionally, we use a combination of microwave fields and laser tones to control the divacancy ground state spin and probe coherence inside the cavity nanostructure. This system represents an advance towards the scalability of long-distance entanglement schemes using SiC that require the interference of indistinguishable photons from spatially separated single defects. |
Wednesday, March 17, 2021 2:06PM - 2:18PM Live |
M29.00012: Coherent control and high-fidelity readout of chromium ions in commercial silicon carbide Berk Diler Kovos, Samuel J Whiteley, Christopher Anderson, Gary Wolfowicz, Marie Elizabeth Wesson, Edward Bielejec, F. Joseph, David Awschalom Transition metal ions provide a rich set of optically active defect spins in wide bandgap semiconductors. Their extrinsic nature promises easy device integration through nano implantation. Specifically, chromium in the 4+ charge state (Cr4+) in silicon carbide (SiC) produces an S = 1 ground state and an S = 0 excited state with a strain insensitive near-telecom Λ-like optical-spin interface. In previous demonstrations the ground state spin control was limited by material quality. In this work [1], we study the formation of Cr4+ in a commercial SiC substrate through implantation and annealing, enabling optical and coherent spin characterization. We measure an ensemble optical hole linewidth of 31 MHz, an order of magnitude narrower compared to as-grown samples. Through a detailed investigation of the Cr4+ governing transition dynamics, we optimize for high readout fidelities (79%). We report T1 times greater than 1 s at T = 15 K with a T2* = 317 ns and a T2 = 81 μs limited by the ensemble density. These results demonstrate Cr4+ in SiC to be an optically active spin-qubit for integration within hybrid quantum devices. |
Wednesday, March 17, 2021 2:18PM - 2:30PM Live |
M29.00013: Wafer-scale electrically tunable quantum nodes in silicon carbide Christopher Anderson, Alexandre Bourassa, Kevin Miao, Mykyta Onizhuk, He Ma, Gary Wolfowicz, Alexander Crook, Peter J Mintun, Hiroshi Abe, Jawad Ul-Hassan, Nguyen T Son, Takeshi Ohshima, Giulia Galli, David Awschalom Defect spin qubits in silicon carbide (SiC) with associated nuclear spin quantum memories [1] can leverage near-telecom emission and wafer-scale semiconductor device engineering [2] for creating quantum technologies. Here, we highlight recent advances with the neutral divacancy (VV0) in SiC within the context of long-distance quantum communication and repeater schemes. We isolate single VV0 defects in functional SiC optoelectronic devices, which allows for deterministic charge state control and terahertz tuning, but also surprisingly eliminates spectral diffusion in the optical structure of these defects. This results in lifetime-limited single-photon emission through semiconductor depletion which offers a generalizable strategy for quantum emitters limited by charge noise. We further discuss the outlook for electrical control, manipulation, and readout of both the spin and charge degrees of freedom in these spin qubits. Combined with the entanglement and control of nuclear spin registers, this work establishes a promising platform for quantum science. |
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