Silicon vacancy centers in 4H-silicon carbide (SiC) host a long-lived electronic spin with spin-resolved optical transitions. This makes them a great candidate for implementing a spin–photon interface, an important building block of quantum networks. However, the fraction of coherently scattered photons is intrinsically low, limiting the achievable communication rates. To address this problem, we integrate V2 centers within a SiC membrane into a fiber-based Fabry–Perot microcavity. We find that SiC is uniquely suited for this approach, offering extremely low losses as we evidence by a high cavity finesse F ≈40000 and naturally available maximal cavity–emitter coupling due to the perfect alignment of polarization modes and the dipole orientation. We observe a 13.3-fold Purcell enhancement of the zero phonon line of a single emitter, constituting an efficient source of coherent photons for this novel material platform, and opening the path toward a deterministic spin–photon interface.
Silicon vacancy centers in 4H-silicon carbide (SiC) host a long-lived electronic spin with spin-resolved optical transitions. This makes them a great candidate for implementing a spin–photon interface, an important building block of quantum networks. However, the fraction of coherently scattered photons is intrinsically low, limiting the achievable communication rates. To address this problem, we integrate V2 centers within a SiC membrane into a fiber-based Fabry–Perot microcavity. We find that SiC is uniquely suited for this approach, offering extremely low losses as we evidence by a high cavity finesse F ≈40000 and naturally available maximal cavity–emitter coupling due to the perfect alignment of polarization modes and the dipole orientation. We observe a 13.3-fold Purcell enhancement of the zero phonon line of a single emitter, constituting an efficient source of coherent photons for this novel material platform, and opening the path toward a deterministic spin–photon interface.
Vanadium color centers in silicon carbide (SiC) offer telecom O-band emission, sub-microsecond optical lifetimes, and second-scale spin relaxation times, rendering them promising candidates for quantum network nodes. However, efficient photon extraction from the high-refractive-index SiC host remains challenging. Here, we introduce a silicon-on-SiC heterogeneous photonic platform in which silicon nanocavities evanescently couple to shallow vanadium dopants in commercial 4H-SiC, enabling efficient zero-phonon line (ZPL) collection under resonant excitation. In as-grown ensembles, we observe Purcell-enhanced photoluminescence with transient spectral hole burning linewidths of 50 MHz on microsecond timescales. In dilute implanted samples, we isolate individual vanadium centers with high-purity single photon emission and a Purcell-enhanced lifetime of 109 ns. The entire optical interface operates through a single lensed fiber, including a 905 nm repump laser that recovers the vanadium charge state with 95% efficiency. These results establish Si-on-SiC as a scalable, foundry-compatible platform for telecom-wavelength spin-photon interfaces.
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.
Implementation of large-scale quantum networks have the potential to augment the capabilities of existing quantum information technologies. By linking quantum processors over photonic channels, future quantum networks could enable applications such as remote quantum sensing, distributed quantum computing, and secure quantum communication. Atomic defects in solids are readily integrated with photonic structures, making them promising candidates for use in quantum networking devices. In particular, the silicon material platform holds great promise due to the technologically mature silicon electronic and photonic industries. The T center defects in silicon possess telecom O-band optical transitions, as well as long-lived electronic and nuclear spins, making it the focus of particular interest. These spin and optical properties of single T centers, together with their accessibility to the existing integrated electronic and photonic technologies, opening the door to modular long-distance quantum networking technologies built on the T center platform. This work outlines the integration of single T centers with a silicon photonic crystal cavity; we observe cavity-enhanced fluorescence emission, resulting in a decay rate enhancement factor of F = 6.89 compared to the bulk emission rate. Through the use of silicon photonic circuits and an angle-polished fiber for light coupling, we achieve a maximum zero phonon line photon outcoupling rate of 73.3 kHz. The design and fabrication of the nanophotonic cavity used in experiment is detailed. This work represents a major step towards use of the silicon T center as a telecom spin-photon interface in future quantum networking applications.
Efficient optical interfacing of spin-bearing quantum emitters is a crucial ingredient for quantum networks. A promising route therefore is to incorporate host materials as minimally processed membranes into open-access microcavities: it enables significant emission enhancement and efficient photon collection, minimizes deteriorating influence on the quantum emitter, and allows for full spatial and spectral tunability. Here, we study the properties of a high-finesse fiber Fabry-P\'erot microcavity with integrated single-crystal diamond membranes by scanning cavity microscopy. We observe the spatially resolved effects of the diamond-air interface on the cavity-mode structure: a strong correlation of the cavity finesse and mode structure with the diamond thickness and surface topography, prevalent transverse-mode mixing under diamondlike conditions, and mode-character-dependent polarization-mode splitting. Our results reveal the influence of the diamond surface on the achievable Purcell enhancement, which helps to clarify the route towards optimized spin-photon interfaces.
This thesis investigates the coupling of the fluorescence of nitrogen-vacancy (NV) centers in diamond to tunable optical microresonators at ambient conditions, in particular in the regime of Purcell enhancement. We use fiber-based, open-access Fabry-Pérot cavities optimized for high finesse and ultra-small mode volume. Different regimes of cavity enhancement are studied that are complementary to each other: A first experiment relies on a high-finesse cavity with dielectric mirrors. The scaling laws of Purcell enhancement are explicitly demonstrated by a large-range variation of both the cavity mode volume (V = 16 − 600 µm^3 ) and the quality factor (Q = 6 · 10^3 − 2 · 10^6). We detect an enhancement of the emission spectral density by up to a factor of 300. The full potential of this resonator can be exploited with emitters having a linewidth which is narrower than the resonance linewidth of the cavity. This concept holds promise for the implementation of wavelength-tunable, narrow-band single-photon sources as well as the generation of indistinguishable single-photons at ambient conditions. However, for broad-band emitters like the NV center at room temperature, the emission lifetime is not affected noticeably in this configuration. In order to directly observe lifetime changes and Purcell-enhanced single-photon emission, we manufacture fiber-based cavities with silver-coated mirrors having ultra-small mode volumes, as small as V = 1.0 λ^3 = 0.34 µm^3. We demonstrate cavity-enhanced fluorescence imaging, which allows to locate and analyze several single NV centers with one cavity. The Purcell effect is evidenced by an enhanced fluorescence collection of up to 1.6 · 10^6 photons per second from single-NV centers and a tunable variation of the emission lifetime corresponding to an effective Purcell factor of up to 2. We furthermore investigate a benefcial regime of optical confinement where the Fabry-Pérot cavity mode is combined with additional mode confinement by the diamond nanocrystal itself, enabling sub-λ^3 mode volumes. We perform simulations that predict effective Purcell factors of up to 11 for NV centers and of up to 63 for silicon-vacancy centers, revealing a great potential for bright single-photon sources and effcient spin readout at ambient conditions.
The tin-vacancy (SnV) center in diamond is a promising spin-photon interface for quantum networks, combining favorable optical properties with spin coherence above 1K. Unfolding the full potential requires cavity enhancement to increase photon-emitter coupling efficiency. Here, we demonstrate cavity-enhanced light-matter coupling of SnV centers in a fully tunable Fabry-Pérot microcavity operating at temperatures down to 1K with in-situ magnetic field control. We access the diamond-like regime of hybrid cavity modes through integration of low-roughness diamond membranes, where the field is concentrated inside the diamond and Purcell enhancement is maximized. Diamond-like modes deliver a more than two-fold increase in the effective Purcell factor over air-like modes, reaching C0=4.1(1) compared to C0=1.85(5) in the air-like case, while simultaneously relaxing mechanical stability requirements. Resonant probing reveals coherent cavity-emitter coupling with 96% extinction contrast and a coherent cooperativity of C=4.0(14). By applying a magnetic field, we further achieve spin-resolved cavity extinction, observing spin-selective optical transitions with a contrast of Cspin=0.91. These results establish SnV centers in diamond coupled to open Fabry-Pérot microcavities as a promising platform for efficient spin-photon interfaces.