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arXiv:1912.05247 · Physical Review Applied

Cavity-Enhanced Photon Emission from a Single Germanium-Vacancy Center in a Diamond Membrane

Rasmus Høy Jensen, Erika Janitz, Yannik Fontana, Yi He, Olivier Gobron, Ilya P. Radko, Mihir K. Bhaskar, Ruffin E. Evans, César Daniel Rodríguez Rosenblueth, Lilian Childress, Alexander Huck, Ulrik L. Andersen

Published Jun 5, 2020• 38 citations
arXivHTMLPDF

Abstract

The nitrogen-vacancy center in diamond has been explored extensively as a light-matter interface for quantum information applications, however, it is limited by low coherent photon emission and spectral instability. Here, we present a promising interface based on an alternative defect with superior optical properties (the germanium-vacancy) coupled to a finesse-11 000 fiber cavity, resulting in a ${31}_{\ensuremath{-}15}^{+11}$-fold increase in the spectral density of zero-phonon-line emission. This work sets the stage for cryogenic experiments, where we predict a measurable increase in the spontaneous emission rate.

DOI
10.1103/physrevapplied.13.064016

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European Quantum Electronics Conference (EQEC)•Jun 21, 2015•0 citations
The nitrogen-vacancy center in diamond has been explored extensively as a light-matter interface for quantum information applications, however, it is limited by low coherent photon emission and spectral instability. Here, we present a promising interface based on an alternative defect with superior optical properties (the germanium-vacancy) coupled to a finesse-11 000 fiber cavity, resulting in a 31\ensuremath−15+11{31}_{\ensuremath{-}15}^{+11}31\ensuremath−15+11​-fold increase in the spectral density of zero-phonon-line emission. This work sets the stage for cryogenic experiments, where we predict a measurable increase in the spontaneous emission rate.
A key requirement for many applications in solid-state quantum sciences is a high fluence of indistinguishable photons. The spontaneous emission of these photons is governed by the coupling of an excited quantum system to electromagnetic vacuum fluctuations. In our experiment, we enhance this coupling by engineering a tunable Fabry-Perot microcavity. The quantum system we study is the nitrogen-vacancy (NV) center in diamond, a workhorse for quantum science and engineering, due to its optical transitions and the coherent electron spin system it hosts. Our device consists of a high-quality, nano-fabricated, single-crystalline diamond membrane bonded to a planar mirror; the cavity is completed by a second, concave mirror. Using piezo positioners, we achieve full spectral and spatial tunability and freedom in selecting NVs with favorable emission properties in our low-temperature (4 Kelvin) experiments. Upon tuning of the cavity into resonance, we find significant enhancement of the 637 nm zero phonon line for several individual NVs which is accompanied by a strong reduction of the overall photoluminescence (PL) lifetime. We infer a 30-fold enhancement of the zero-phonon transition rate at best. The fraction of the PL emission associated to this resonant transition is thereby increased from 3% to 46%. Our results constitute a significant leap on the route towards the implementation of fast long-distance quantum networks, which are currently limited by the photon emission rate in their nodes. Furthermore, our versatile design is readily applicable to other solid-state quantum emitters like color centers in silicon carbide.
Recent demonstrations of entanglement between two remote Nitrogen-Vacancy centers, have opened the way for their use in distributed quantum networks. An efficient spin-photon interface will now be required to help realize this system as a technology. Here we demonstrate the tunable enhancement of the zero phonon line of a single nitrogen-vacancy colour centre in nanodiamond at cryogenic temperatures. A plano-hemispherical open cavity, fabricated using focused ion beam milling provides mode volumes as small as 1.25 cubic microns and quality factor Q ~ 3000. It will be shown how the open geometry and independently adjustable mirrors allows for precise placement of the emitter in the centre of the cavity mode, and crucially enables in-situ tuning of the cavity resonances. At optimal coupling, the signal from individual zero phonon line transitions is enhanced by a factor of 6.25 through the Purcell effect and the overall emission rate of the NV- centre is increased by 40% compared with that measured from the same centre in the absence of cavity field confinement. This Purcell enhancement is mapped out as a function of cavity mode volume. These results represent a proof of principle for a tunable cryogenic spin-photon interface. However by far the best NV optical and spin coherences are to be found in bulk material and efforts towards the production of diamond membranes are currently being made, with dimensions suitable for open-cavity coupling. Efforts towards this and preliminary results will also be discussed.
The unique correlations in quantum systems, i.e. superposition and entanglement, enable quantum technologies to outperform classical technologies. Quantum networks is a quantum technology in fast development with many promising applications. An essential building block in a quantum network is the interface between matter nodes and quantum channels. A color center in diamond coupled to a micro-cavity is a promising route to achieve an efficient interface. In this thesis we investigate the coupling of a single germanium vacancy (GeV) center to a Fabry-Pérot optical micro-cavity at room temperature. The Fabry-Pérot optical micro-cavity was formed by a macroscopic flat mirror and a fiber-based concave microscopic mirror. The concave mirror was created on the end-facet of a fiber with short high power laser pulses from a CO2-laser. High qulity dielectric coating allowed us to achieve a finesse of 11,000 with a∼1 µm thin diamond membrane incorporated in the cavity. We achieved a cavity length of only a few µm and a small mode volume V = 2.7µm, which was essential for good coupling between the GeV center and the optical cavity mode. By studying the same GeV center in a confocal microscope setup, i.e. outside of the micro-cavity, and in the micro-cavity setup, we were able to measure an improved optical coherence of the GeV emission in the cavity. We determined an enhancement of the spectral density by a factor of ∼15. Furthermore, we determined the emission efficiency into the cavity mode β and compared it with the theoretical modelling. From the theoretical modelling, we predict the expected Purcell factor Fp = 200 for the zero phonon line in future experiments at cryogenic temperatures. Going to cryogenic temperatures is necessary to achieve efficient spin-photon interfaces. This work provides valuable information for realizing efficient spin-photon interfaces, which is critical for the practical implementation of a quantum network.
Color centers in diamond, among them the negatively charged germanium vacancy (GeV−), are promising candidates for many applications of quantum optics, such as a quantum network. For efficient implementation, the optical transitions need to be coupled to a single optical mode. Here, we demonstrate the transfer of a nanodiamond containing a single ingrown GeV− center with excellent optical properties to an open Fabry–Pérot microcavity by nanomanipulation utilizing an atomic force microscope. Coupling of the GeV− defect to the cavity mode is achieved, while the optical resonator maintains a high finesse of F=7700, and a 48-fold spectral density enhancement is observed. This article demonstrates the integration of a GeV− defect with a Fabry–Pérot microcavity under ambient conditions with the potential to extend the experiments to cryogenic temperatures toward an efficient spin-photon platform.
The realisation of an efficient spin-photon interface using the negatively charged nitrogen-vacancy centre (NV-) in diamond requires the resonant coupling of the zero phonon line (ZPL) of the centre to an optical microcavity [1]. The cavity serves to encourage emission into the ZPL in preference to the phonon sidebands, and potentially also to increase the homogeneous linewidth via a reduction of the lifetime (the Purcell effect) thus assisting in the generation of indistinguishable photons. Cavity coupling thus has potential to improve by orders of magnitude the speed with which entanglement can be created between spatially remote NV- centres [2], and to enable other mechanisms for realising spin-photon interfaces via non-demolition measurements [3].