Cavity-Enhanced Measurements of Defect Spins in Silicon Carbide

Greg Calusine, Alberto Politi, and David D. Awschalom

Phys. Rev. Applied 6, 014019 – Published 29 July 2016

Abstract

The identification of new solid-state defect-qubit candidates in widely used semiconductors has the potential to enable the use of nanofabricated devices for enhanced qubit measurement and control operations. In particular, the recent discovery of optically active spin states in silicon carbide thin films offers a scalable route for incorporating defect qubits into on-chip photonic devices. Here, we demonstrate the use of 3C silicon carbide photonic crystal cavities for enhanced excitation of color-center defect spin ensembles in order to increase measured photoluminescence signal count rates, optically detected magnetic-resonance signal intensities, and optical spin initialization rates. We observe an up to a factor of 30 increase in the photoluminescence and optically detected magnetic-resonance signals from Ky5 color centers excited by cavity-resonant excitation and increase the rate of ground-state spin initialization by approximately a factor of 2. Furthermore, we show that the 705-fold reduction in excitation mode volume and enhanced excitation and collection efficiencies provided by the structures can be used to overcome inhomogenous broadening in order to facilitate the study of defect-qubit subensemble properties. These results highlight some of the benefits that nanofabricated devices offer for engineering the local photonic environment of color-center defect qubits to enable applications in quantum information and sensing.

Received 7 October 2015

DOI:https://doi.org/10.1103/PhysRevApplied.6.014019

Physics Subject Headings (PhySH)

Color centers Photonic crystals Point defects Quantum information architectures & platforms Quantum information with solid state qubits

Optically detected magnetic resonance Photoluminescence

Atomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Greg Calusine¹, Alberto Politi^1,2, and David D. Awschalom^1,3,*

¹Department of Physics, University of California, Santa Barbara, California 93106, USA
²School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom
³Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA

^*awsch@uchicago.edu

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Vol. 6, Iss. 1 — July 2016

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Images

Figure 1
(a) Simulation of the $L 3$ cavity electric-field intensity enhancement relative to an incident Gaussian beam ( $1 − μ m$ beam waist indicated by the dashed red lines) with unity electric-field amplitude maximum. Note the change in scale above and below the dashed green line. The dashed white lines delineate the cross sections of the photonic-crystal-cavity holes. (b) Diagram depicting the CEPLE scheme overlaid on top of the off-resonantly-excited PL spectrum of an $L 3$ cavity with incorporated Ky5 centers at 20 K. (c) (top panel) Fine structure within the Ky5 ZPL for different implantation doses. (bottom panel) $H 1$ cavity resonances in the Ky5 fluorescence spectrum for films with different implantation doses (black and blue lines) and corresponding PLE measurements of the observed fine structure (magenta line). All curves are scaled for ease of comparison.
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Figure 2
(a) SEM image of the $3 C − SiC$ $L 3$ cavity structure. (b) and (c) $15 μ m \times 15 μ m$ spatial scans of the sideband PL intensity signal for the excitation wavelengths depicted in (d) [(b) $λ_{1} = 1115.1 nm$ , (c) $λ_{2} = 1117.1 nm$ ]. The white dashed lines indicate the extent of the photonic crystal. The count rate measured on the cavity in (c) is $\sim 48 kcounts / s$ . (d) Sideband PL count rate vs excitation wavelength measured at the position of the cavity. (e) Linecut along the dashed red line in (c).
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Figure 3
(a) Optical image of a photonic-crystal-cavity array with a $50 − μ m − wide$ $10 nm / 300 nm$ Ti/Au microstrip positioned $50 μ m$ away from the cavities. (b) ODMR signal at 1.319 GHz measured on the photonic crystal cavity (black line and dots) and on the $3 C − SiC$ thin film (red line and dots) for excitation at the same power at the cavity resonance wavelength. (c) Pulsed ODMR signal from a Ky5 ensemble subject to cavity-enhanced excitation (red line and dots) as compared to an ensemble within the thin film (black line and dots). The blue line and dots show the same measurement for defects within the thin film for a higher optical-excitation power (offset for clarity).
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Figure 4
(a) Pulse sequences for measuring spin-dependent PL dynamics of Ky5 centers using a variable-length laser excitation pulse (not to scale). (b) Simulated time-dependent difference in PL for a generic OPCC initialized into the $m_{s} = 0$ vs $m_{s} = \pm 1$ ground state for two excitation rates differing by a factor of 3. The red lines depict exponential fits to the time scales that correspond to an approximately exponential saturation of the ground-state spin polarization. The black curve is offset for clarity. (c) Measured PL difference signal for an ensemble of Ky5 defects within an $L 3$ photonic crystal cavity excited on resonance (black line and dots) as compared with an ensemble excited within the unpatterned thin film (blue line and dots) at the same power and wavelength. The red lines represent simulated behavior as predicted by the model discussed in the main text. The time constants result from exponential fits to the data.
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