Purcell-Enhanced Single-Photon Emission from Nitrogen-Vacancy Centers Coupled to a Tunable Microcavity

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Purcell-Enhanced Single-Photon Emission from Nitrogen-Vacancy Centers Coupled to a Tunable Microcavity

Hanno Kaupp, Thomas Hümmer, Matthias Mader, Benedikt Schlederer, Julia Benedikter, Philip Haeusser, Huan-Cheng Chang, Helmut Fedder, Theodor W. Hänsch, and David Hunger

Phys. Rev. Applied 6, 054010 – Published 22 November 2016

Abstract

Optical microcavities are a powerful tool for enhancing the fluorescence of individual quantum emitters. However, the broad emission spectra encountered in the solid state at room temperature limit the influence of a cavity, calling for an ultrasmall mode volume. We demonstrate Purcell-enhanced single-photon emission from nitrogen-vacancy centers in nanodiamonds coupled to a tunable fiber-based microcavity with a mode volume down to $1.0 λ^{3}$ . We record cavity-enhanced fluorescence images and study several single emitters with one cavity. The Purcell effect is evidenced by enhanced fluorescence collection and tunable lifetime modification, and we infer an effective Purcell factor of up to 2. Furthermore, we show an alternative regime for light confinement, where a Fabry-Perot mode is combined with additional mode confinement by the nanocrystal itself. Simulations predict effective Purcell factors of up to 11 for nitrogen-vacancy centers and 63 for silicon-vacancy centers, holding promise for bright single-photon sources and efficient spin readout under ambient conditions.

Received 9 May 2016

DOI:https://doi.org/10.1103/PhysRevApplied.6.054010

Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 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)

Optical microcavities Quantum information processing

Nanostructures Nitrogen vacancy centers in diamond

Fabry-Pérot interferometry Fluorescence Optical microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Hanno Kaupp^1,2, Thomas Hümmer^1,2, Matthias Mader^1,2, Benedikt Schlederer¹, Julia Benedikter^1,2, Philip Haeusser¹, Huan-Cheng Chang³, Helmut Fedder⁴, Theodor W. Hänsch^1,2, and David Hunger^1,2,*

¹Fakultät für Physik, Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany
²Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
³Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan
⁴3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany

^*david.hunger@physik.lmu.de

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Vol. 6, Iss. 5 — November 2016

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Images

Figure 1
(a) Sketch of the cavity consisting of a laser-machined and mirror-coated fiber and a macroscopic mirror carrying nanodiamonds with NV centers. The large mirror is mounted on a three-axis nanopositioning stage for spatial scanning, the cavity length is controlled by an additional piezoelectric actuator. (b) Microscope images of two laser-shaped fiber tips. (c) 3D profile of a laser-machined and silver-coated fiber tip. (d) Cut through the center of the structure shown in (c) (the blue curve) together with a parabolic fit (the red curve). (e) Cavity transmission probed with a narrow-band laser as a function of the cavity length. (f) Series of cavity transmission spectra under broadband illumination as a function of the cavity length, showing tunability for cavity lengths down to $λ_{0} / 2$ . (g) Individual spectra from (f) for different mode orders $q$ .
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Figure 2
(a) Cavity-enhanced flourescence image showing several single emitters (the circles). The cavity length is stabilized on resonance with the excitation light at a length of about $10 μ m$ while scanned laterally. (b) Cavity scan of a single-NV center at 1.1- $μ m$ cavity length. (c) Vertical cut through the scan in (b) together with a Gaussian fit, yielding $w_{\det} = 1.1 μ m$ . (d) Measured size of the point-spread function (the blue points) as a function of the cavity length, together with the value calculated from the radius of curvature of the fiber mirror (the blue line). Mode volume calculated from the measured $w_{\det}$ (the green points), together with the expected value (the green line).
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Figure 3
(a) Autocorrelation measurement for NV1 yielding $g^{(2)} (0) = 0.27$ without background subtraction. (b) Saturation measurement (the green dots) with a fit of the same NV center. Background fluorescence (the purple dots) with a linear fit. NV-center fluorescence subtracted by the background (the black dashed line). (c) Comparison of the saturation count rates and single-photon purities for NV centers on glass (the blue dots) and inside the cavity at $d = 1.1 μ m$ (the red dots). An average enhancement by a factor of 3.8 is found. (d) Lifetime measurement of NV1 at $d = 2 μ m$ (black) and $d = λ_{0} / 2$ (brown) with monoexponential fits.
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Figure 4
(a) Measured lifetime $τ (d_{0})$ as a function of the mirror separation (gray dots) together with FDTD simulations for a diamond cube of edge length 30 nm (black line) and 155 nm (red line). The filled colored dots indicate the positions at which the data sets shown in (b) are taken. The yellow area shows the distance range where the fiber touches the large diamond. (b) Lifetime traces for different cavity lengths with fits (black), (red: $τ = 11.2 ns$ , blue: 19.3 ns, green: 23.9 ns). (c) Cavity emission spectra at resonances corresponding to longitudinal mode orders $q = 1$ , 2, 7. (d) Simulation of the intensity distribution of a dipole located at the center (logarithmic scale, red: high, blue: low). The intensity is confined between the two silver mirrors (horizontal black lines, including the spacer layers) and localized to the nanocrystal (black square). Outcoupling occurs predominantly through the thinner bottom mirror. (e) Simulated Purcell factor as a function of the wavelength for a 155 nm (red, corresponding to open circle in (a)) and a 30 nm (black) diamond.
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