Broadband Light Extraction from Near-Surface NV Centers Using Crystalline-Silicon Antennas
Minjeong Kim, Maryam Zahedian, Wenxin Wu, Chengyu Fang, Zhaoning Yu, Raymond A. Wambold, Ricardo Vidrio, Yuhan Tong, Shenwei Yin, David A. Czaplewski, Jennifer T. Choy, Mikhail A. Kats
We use crystalline silicon (Si) antennas to efficiently extract broadband single-photon fluorescence from shallow nitrogen-vacancy (NV) centers in diamond into free space. Our design features relatively easy-to-pattern high-index Si resonators on the diamond surface to boost photon extraction by overcoming total internal reflection and Fresnel reflection at the diamond-air interface and providing modest Purcell enhancement, without etching or otherwise damaging the diamond surface. In simulations, ∼17 times more single photons are collected from a single NV center compared to the case without the antenna; in experiments, we observe an enhancement of ∼9 times, limited by spatial alignment between the NV and the antenna. Our approach can be readily applied to other color centers in diamond, and more generally to the extraction of light from quantum emitters in wide-bandgap materials.
We use crystalline silicon (Si) antennas to efficiently extract broadband single-photon fluorescence from shallow nitrogen-vacancy (NV) centers in diamond into free space. Our design features relatively easy-to-pattern high-index Si resonators on the diamond surface to boost photon extraction by overcoming total internal reflection and Fresnel reflection at the diamond-air interface and providing modest Purcell enhancement, without etching or otherwise damaging the diamond surface. In simulations, ∼17 times more single photons are collected from a single NV center compared to the case without the antenna; in experiments, we observe an enhancement of ∼9 times, limited by spatial alignment between the NV and the antenna. Our approach can be readily applied to other color centers in diamond, and more generally to the extraction of light from quantum emitters in wide-bandgap materials.
Silicon-vacancy (SiV) color centers in diamond offer novel possibilities to probe light-matter interaction in nano-quantum optics and provide a scalable quantum system suitable for single-photon emission. However, their effective count-rate is still limited by non-radiative decay channels, radiation at wide angles and total internal reflection at the diamond interface. Recently optical antennas have been utilized in order to modify light-matter interaction at the nanoscale. Acting as resonators, they are able to increase the spontaneous emission rate of quantum emitters by several orders of magnitude in a broad spectral range. Because coupling a quantum emitter to a nano-antenna requires close proximity between the two systems, we implant Si ions on very thin diamond membranes that provide the required dimension for near-field interaction in a controlled manner and investigate the optical properties of SiV color centers in such diamond membranes. We consider gold nano-cones as nano-antennas, fabricated by focused electron beam induced deposition (EBID), followed by sputtering and focused ion beam (FIB) milling. The finite-difference time-domain (FDTD) calculations show that gold nano-cones can provide more than four orders of magnitude enhancement in the Purcell factor with an antenna efficiency (AE) of 80%.
The nitrogen-vacancy (NV) center in diamond has an optically addressable, highly coherent spin. However, an NV center even in high quality single-crystalline material is a very poor source of single photons: extraction out of the high-index diamond is inefficient, the emission of coherent photons represents just a few per cent of the total emission, and the decay time is large. In principle, all three problems can be addressed with a resonant microcavity, which significantly boosts the emission rate of coherent photons into the cavity mode based on the Purcell effect. In practice though, it has proved difficult to implement this concept: photonic engineering hinges on nano-fabrication yet it is notoriously difficult to process diamond without degrading the NV centers. \nIn this thesis, we present a microcavity scheme which employs minimally processed diamond membranes, thereby preserving the high quality of the starting material. The miniaturized plano-concave Fabry-Perot microcavity platform features full in situ spatial and spectral tunability. We demonstrate a clear change in the lifetime for multiple individual NV centers on tuning both the cavity frequency and anti-node position. The overall Purcell factor for the zero-phonon line (ZPL) of ~30 translates to an increase in the ZPL emission probability from ~3% to ~46%. \nFurthermore, we report the creation of a low-loss, broadband optical antenna giving highly directed output from a coherent single spin in the solid state. The device, the first crystalline solid-state realization of a dielectric antenna, is engineered for individual NV electronic spins in diamond. The photonic structure preserves the high spin coherence of single-crystalline diamond (T2 ~100µs). We demonstrate a directionality of close to 10 and single photon count rates approaching one MHz. The analysis of the angular emission pattern of our device suggests that 95% of the broadband NV fluorescence is channeled into a solid angle corresponding to a numerical aperture of 0.8. \nThe abovementioned approaches feature complementary benefits. The narrowband enhancement of the ZPL emission rate provided by the microcavity benefits applications in quantum information processing relying on coherent photons. With the prospect of integrating lifetime-limited emitters and achieving a high ZPL collection efficiency our results pave the way for much enhanced spin-photon and spin-spin entanglement rates. On the other hand, by channeling the major fraction of the broadband NV fluorescence into a narrow solid angle the dielectric optical antenna facilitates efficient spin readout. Our approach enables a near-unity collection efficiency which, upon mitigation of the known photon losses, renders it a potential key technology for quantum sensing applications. \n
Quantum emitters in solids are being developed for a range of quantum technologies, including quantum networks, computing, and sensing. However, a remaining challenge is the poor photon collection due to the high refractive index of most host materials. Here we overcome this limitation by introducing monolithic parabolic reflectors as an efficient geometry for broadband photon extraction from quantum emitter and experimentally demonstrate this device for the nitrogen-vacancy (NV) center in diamond. Simulations indicate a photon collection efficiency exceeding 75% across the visible spectrum and experimental devices, fabricated using a high-throughput gray scale lithography process, demonstrating a photon extraction efficiency of (41 ± 5)%. This device enables a raw experimental detection efficiency of (12 ± 1)% with fluorescence detection rates as high as (4.114 ± 0.003) × 10 6 counts per second (cps) from a single NV center. Enabled by our deterministic emitter localization and fabrication process, we find a high number of exceptional devices with an average count rate of (3.1 ± 0.9) × 10 6 cps.
An efficient atom–photon interface is a key requirement for the integration of solid-state emitters, such as color centers in diamond, into quantum technology applications. As other solid-state emitters, however, their emission into free space is severely limited due to the high refractive index of the bulk host crystal. In this work, we present a planar optical antenna based on two silver mirrors coated on a thin single crystal diamond membrane, forming a planar Fabry–Pérot cavity that improves the photon extraction from single tin vacancy (SnV) centers and their coupling to an excitation laser. Upon numerical optimization of the structure, we find theoretical enhancements in the collectible photon rate by a factor of 60 as compared to the bulk case. As a proof-of-principle demonstration, we fabricate single crystal diamond membranes with sub-μm thickness and create SnV centers by ion implantation. Employing off-resonant excitation, we show a sixfold enhancement of the collectible photon rate, yielding up to half a million photons per second from a single SnV center. At the same time, we observe a significant reduction of the required excitation power in accordance with theory, demonstrating the functionality of the cavity as an optical antenna. Due to its planar design, the antenna simultaneously provides similar enhancements for a large number of emitters inside the membrane. Furthermore, the monolithic structure provides high mechanical stability and straightforwardly enables operation under cryogenic conditions as required in most spin–photon interface implementations.
Enhancing the collection efficiency of single emitters via dielectric antennas is a common approach in research dealing with solid-state quantum light sources. Current design concepts often suffer from a large footprint, quenching or a complex fabrication process. Here we report on another design where the Kerker effect is used to collimate emission from a nitrogen vacancy (NV) center. The structure discussed here is an easy to fabricate cylindrical protrusion made from diamond on top of a diamond substrate with NVs incorporated into its center. We optimize the structure with respect to application in quantum information processing and quantum sensing and find an up to 15 times higher photon extraction.
Efficient collection of fluorescence light is essential for all optically adressable qubit platforms. For the nitrogen-vacancy (NV) center in diamond, the high refractive index of the host medium poses a major challenge as it limits the solid angle under which fluorescence light can leave the crystal. To enhance collection efficiency from single NV centers, we design and simulate micro-optical elements that shall be directly fabricated on the diamond surface using two-photon polymerization. Several optical designs and photoresists are evaluated for their expected coupling efficiency into single-mode fibers and their tolerance to fabrication errors. Additionally, an analytical solution for single lens collimation of the emission of a point source in diamond at a specific wavelength is presented, as well as considerations regarding the degradation of wavefront quality in multi-wavelength Fresnel designs.