Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface

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Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface

David J. Christle, Paul V. Klimov, Charles F. de las Casas, Krisztián Szász, Viktor Ivády, Valdas Jokubavicius, Jawad Ul Hassan, Mikael Syväjärvi, William F. Koehl, Takeshi Ohshima, Nguyen T. Son, Erik Janzén, Ádám Gali, and David D. Awschalom

Phys. Rev. X 7, 021046 – Published 23 June 2017

Abstract

The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a high-fidelity spin-photon interface, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here, we demonstrate that such an interface exists in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have a millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on Si shows promise for future quantum networks based on SiC defects.

Received 20 February 2017

DOI:https://doi.org/10.1103/PhysRevX.7.021046

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Color centers Defects Quantum control Quantum information with solid state qubits Spintronics

Quantum Information, Science & TechnologyCondensed Matter, Materials & Applied Physics

Authors & Affiliations

David J. Christle¹, Paul V. Klimov¹, Charles F. de las Casas¹, Krisztián Szász², Viktor Ivády^2,3, Valdas Jokubavicius³, Jawad Ul Hassan³, Mikael Syväjärvi³, William F. Koehl¹, Takeshi Ohshima⁴, Nguyen T. Son³, Erik Janzén³, Ádám Gali^2,5, and David D. Awschalom^1,*

¹Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
²Wigner Research Centre for Physics, Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, PO Box 49, H-1525, Budapest, Hungary
³Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden
⁴National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
⁵Department of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8., H-1111, Budapest, Hungary

^*awsch@uchicago.edu

Popular Summary

Silicon carbide (SiC) is a high-performance commercial semiconductor that hosts atom-scale defects called divacancies whose quantum spins can be controlled using light and microwaves. Since they reside in solid-state materials and emit light near wavelengths used by telecommunication devices, divacancies could be useful building blocks in future technologies such as quantum networks, where distant quantum states are linked together using light. However, these applications require demanding capabilities such as the ability to communicate with single defects and an interface that can coherently link the defect’s spin with light. We show that divacancies can be isolated in 3C-SiC (a form of SiC with advantages for photonics) and 4H-SiC (a form of SiC most popular for electronics) and that divacancies in both forms of SiC possess an optical interface that will allow for coherent transfer of quantum information between their spins and light.

We grow separate samples with epilayers of 3C-SiC and 4H-SiC that have low intrinsic defect densities and irradiate them with a low dose of electrons so that when annealed, single divacancies can be individually addressed and controlled using microwaves in our home-built confocal microscopy apparatus. We find that 3C-SiC divacancies maintain their quantum phase coherence almost 40 times as long as previous measurements. By cooling to 8 K and exciting single divacancies with a laser, we find a spectrum of highly spin-dependent optical transitions in both forms of SiC. These transitions enable nearly perfect optical contrast when detecting the divacancy’s spin state, which is a substantial improvement on previous work. By carefully measuring the strength of intrinsic spin-orbit and spin-spin interactions, we show how these transitions can serve as a high-fidelity coherent interface between the divacancy’s spin and near-telecom photons.

Our results demonstrate that divacancy defects are well suited to serve as nodes in a quantum network operating at telecom wavelengths.

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Vol. 7, Iss. 2 — April - June 2017

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Figure 1
Isolation and control of single spins in 3C-SiC. (a) A typical two-dimensional photoluminescence scan showing single defects as isolated luminescent spots in 3C-SiC. (b) Photon antibunching observed in the background-corrected photon correlation measurement taken on an isolated photoluminescence spot. The green dashed line indicates the 0.5 threshold below which the emission is consistent with a single quantum emitter. Our analysis indicates $g^{2} (τ = 0) = ({0.055}_{- 0.047}^{+ 0.044})$ at the 95% probability level, which confirms we have isolated a single defect. (c) A measurement of Rabi oscillations recorded on the same defect, which shows an approximate off-resonant readout contrast of 7.5%. (d) Hahn-echo measurement performed on an ensemble of Ky5/L3 defects in the higher-irradiation 3C-SiC sample ( $1 \times 10^{15} {cm}^{- 2}$ fluence) at $T = 20 K$ and $B = 253 G$ , showing $T_{2} = (901 \pm 51) μ s$ .
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Figure 2
Excited-state fine structure of 4H- and 3C-SiC divacancies. (a) Left: Level diagram of the ${}^{3}E$ excited state, showing the effect of axial spin-orbit coupling, the three spin-spin interactions, and transverse strain. Right: Diagram of optical transitions excited in a PLE measurement that are nominally spin-conserving at low strain, which are near 264 930 GHz for ( $h h$ ) divacancies. Microwave driving near $D = 1.34 GHz$ is applied to produce a mixed time-averaged population in the ground state so that all six transitions can be observed. (b) Photoluminescence excitation measurements taken on a single 4H-SiC ( $h h$ ) divacancy with a transverse strain of $δ_{⊥} = 7 GHz$ at $T = 8 K$ under continuous microwave driving. (c) Individual resonances recorded at $T = 8 K$ on separate ( $h h$ ) divacancies that experience different magnitudes of transverse strain. The solid lines are the Hamiltonian energies at the best fit value. (d) Photoluminescence excitation measurements taken $T = 8 K$ on single 3C-SiC divacancies that experience different transverse strains. The estimated magnitude of the transverse strain is labeled in units of GHz on each trace. The solid lines are fits to a sum of Lorentzians intended only as a guide to the eye since the larger linewidths make the number of spin-conserving and spin-nonconserving transitions that are visible uncertain.
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Figure 3
Characterization of divacancy optical transition properties. (a) Temperature dependence of the optical linewidths of different inequivalent 3C-SiC and 4H-SiC divacancy defects. (b) Single-spin Rabi oscillations recorded using the $E_{y}$ transition of a single 4H-SiC ( $h h$ ) divacancy at $T = 8 K$ and $B = 15 G$ with a transverse strain of $δ_{⊥} = 27 GHz$ . The measurement gives a background-corrected readout contrast of 94%, consistent with a high degree of spin polarization. (c) The spin-flip rate as a function of resonant laser power measured on different $E_{x}$ and $E_{y}$ transitions on different single 4H-SiC divacancies.
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Figure 4
Dynamical model of the 3C-SiC divacancy. (a) Diagram of the levels and major rates in the five-level rate-equation model. The transition rates and ground-state spin polarization are inferred from the global fit described in the main text. (b) Normalized log plot of the fluorescence recorded on a single 3C-SiC divacancy. The $θ = 0$ data are the time-resolved PL when no microwaves are applied and the spin remains in $m_{s} = 0$ , while the $θ = π$ data are taken after a microwave $π$ pulse prepares the spin in the $m_{s} = - 1$ state. The small gaps originate from a preprocessing step where small pulses imperfectly extinguished by our electro-optic modulator are removed. (c) Normalized single divacancy photoluminescence emitted at the beginning off-resonant cw laser pulses of different powers. The upper trace in each subpanel is the PL observed when the spin is prepared in $m_{s} = 0$ , while the respective lower traces are observed when a microwave $π$ pulse rotates the spin into $m_{s} = - 1$ . Solid lines are the corresponding global fits of the rate-equation model.
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