Abstract Silicon is a leading material platform for photonic quantum technologies. However, a key challenge remains the efficient integration of high-performance single-photon sources in the near infrared. Here we present an all-silicon single-photon source at 1217 nm wavelength, fabricated by nanoscale positioning of a single W center in a circular Bragg grating cavity. The operation wavelength corresponds to the W center’s zero-phonon line that is enhanced by the cavity. Under above-gap continuous-wave excitation, we obtain a saturated photon count rate of 1.29 × 10 6 counts/s with pronounced photon antibunching ( g (2) (0) = 0.06 ± 0.02). Triggered operation under weak pulsed excitation produces single photons with 93 ± 2% purity. At saturation, we reveal purity degradation due to repumping processes, that could be mitigated using selective excitation schemes in the future. These results represent a major step towards on-demand sources of indistinguishable single photons in silicon photonics.
Abstract Silicon is a leading material platform for photonic quantum technologies. However, a key challenge remains the efficient integration of high-performance single-photon sources in the near infrared. Here we present an all-silicon single-photon source at 1217 nm wavelength, fabricated by nanoscale positioning of a single W center in a circular Bragg grating cavity. The operation wavelength corresponds to the W center’s zero-phonon line that is enhanced by the cavity. Under above-gap continuous-wave excitation, we obtain a saturated photon count rate of 1.29 × 10 6 counts/s with pronounced photon antibunching ( g (2) (0) = 0.06 ± 0.02). Triggered operation under weak pulsed excitation produces single photons with 93 ± 2% purity. At saturation, we reveal purity degradation due to repumping processes, that could be mitigated using selective excitation schemes in the future. These results represent a major step towards on-demand sources of indistinguishable single photons in silicon photonics.
Photons are excellent carriers of quantum information. The generation, manipulation and read-out of photonic quantum states have enabled pioneering investigations in quantum physics, paving the way to groundbreaking technologies. Integrated quantum photonics, that is the processing of photons on-chip, is at the forefront of this revolution. In particular, silicon integrated circuits have emerged as the dominant material platform for large-scale quantum photonics. However, the difficulty to inject single photons on-demand in a silicon chip is a major obstacle to the level of complexity of current systems. In this context, the isolation of individual fluorescent defects in silicon, called color centers, opens an avenue toward the integration of atomic sources of single photons. While several color centers have demonstrated an ability to generate antibunched photons, practical applications require tailoring of their emission through quantum electrodynamics effects in optical cavities.This PhD thesis is devoted to cavity quantum electrodynamics with color centers in silicon optical cavities, in view of building an efficient source of single photons. The efforts are first focused on ensembles of G centers in microring cavities. The optical properties of cavity-coupled G centers are studied using microphotoluminescence spectroscopy, and an enhancement of their zero-phonon emission rate by Purcell effect is demonstrated. However, a quantitative analysis reveals a poor quantum efficiency, motivating the choice of another emitter for further experiments. Subsequently, the efforts are focused on the W center. Purcell enhancement of the overall recombination rate is observed for an ensemble of W centers in a circular Bragg grating cavity. Using a quantitative analysis based on finite-difference time-domain calculation, a high quantum efficiency is estimated. The results being encouraging for the purpose of single photon emission, an optical setup is developed for single-emitter spectroscopy and a strategy is devised to fabricate individually-adressable emitters, leading to the isolation of single W centers in unpatterned silicon-on-insulator. Using a nanofabrication process allowing for deterministic positionning, the emitters are embedded into circular Bragg grating cavities, resulting in an increase of the photoluminescence intensity by orders of magnitude by Purcell effect. This work leads to the demonstration of a source of triggered single photons.A next milestone will be the demonstration of a single photon source for integrated photonic circuits, based on a color center in a waveguide-coupled optical cavity. Beyond the interest for integrated quantum photonics, the observation of bright photoluminescence from single color centers opens perspectives for further experiments, allowing to probe fundamental questions relative to their photophysics.
Monolithic integration of single-photon sources into silicon photonics offers a compelling solution for realizing scalable quantum telecommunication architectures. Among the candidate silicon color centers, the C-center features a zero-phonon emission in the telecom L-band, corresponding to the spectral window of minimum transmission loss in optical fibers. Despite this advantage, isolating single C-centers has remained an unrealized challenge in solid-state quantum optics. In this work, we report the isolation of a single silicon C-center. We enhance the spontaneous emission rate of the zero-phonon line by coupling the single emitter to a nanophotonic crystal cavity, observing a fivefold reduction in the excited-state lifetime compared to bulk conditions, which corresponds to a Purcell factor lower bound of 33. Second-order autocorrelation measurements confirm single-photon emission from the investigated defect, obtaining an optical purity of g(2)(0)=0.23 without background correction. Our results establish a native telecom L-band quantum light source in silicon, laying the foundation for ultra-low-loss and long-distance quantum applications.
Silicon-based semiconductor nanofabrication technology has achieved a remarkable level of sophistication and maturity, and color centers in silicon naturally inherit this advantage. Besides, their emissions appear in telecommunication bands, which makes them play a crucial role in the construction of a quantum network. To address the challenge of weak spontaneous emission, different optical cavities are fabricated to enhance the emission rate. However, the relative location between cavity and emitter is random, which greatly reduces the success probability of enhancement. Here, we report on a fluorescence-localization technique (FLT) for precisely locating a single G center in silicon and embedding it in the center of a circular Bragg grating cavity in situ, achieving 240-times improvement of the success probability. We observe a 30-fold enhancement of luminescence, 2.5-fold acceleration of the emission from a single G center, corresponding to a Purcell factor exceeding 11. Our findings pave the way for large-scale integration of quantum light sources.
Generating single photons on demand in silicon is a challenge to the scalability of silicon-on-insulator integrated quantum photonic chips. While several defects acting as artificial atoms have recently demonstrated an ability to generate antibunched single photons, practical applications require tailoring of their emission through quantum cavity effects. In this work, we perform cavity quantum electrodynamics experiments with ensembles of artificial atoms embedded in silicon-on-insulator microresonators. The emitters under study, known as W color centers, are silicon tri-interstitial defects created upon self-ion implantation and thermal annealing. The resonators consist of circular Bragg grating cavities, designed for moderate Purcell enhancement ( F p = 12.5) and efficient luminescence extraction (η coll = 40% for a numerical aperture of 0.26) for W centers located at the mode antinode. When the resonant frequency mode of the cavity is tuned with the zero-phonon transition of the emitters at 1218 nm, we observe a 20-fold enhancement of the zero-phonon line intensity, together with a 2-fold decrease of the total relaxation time in time-resolved photoluminescence experiments. Based on finite-difference time-domain simulations, we propose a detailed theoretical analysis of Purcell enhancement for an ensemble of W centers, considering the overlap between the emitters and the resonant cavity mode. We obtain a good agreement with our experimental results assuming a quantum efficiency of 65 ± 10% for the emitters in bulk silicon. Therefore, W centers open promising perspectives for the development of on-demand sources of single photons by harnessing cavity quantum electrodynamics in silicon photonic chips.
Sources of individual photons have applications in quantum cryptography, computation, and metrology, but truly scalable sources are still needed. The authors couple silicon-vacancy centers to a high-Q microcavity, yielding a room-temperature source with the potential for high efficiency, brightness, and spectral purity. This setup improves spectral density by more than two orders of magnitude and could offer single-photon rates above 1 GHz, as well as generation of indistinguishable photons.
Silicon G centers show significant promise as single photon sources in a scalable silicon platform. But these color centers have large nonradiative decay and a low Debye-Waller factor, limiting their usability in quantum applications. In this work, we demonstrate bright Purcell-enhanced emission from a silicon G center by coupling it to a nanophotonic cavity. The nanobeam cavity enhances the spontaneous emission rate of a single G center by a factor of 6, corresponding to a Purcell factor greater than 31 when accounting for decay into the phonon sideband. We obtain a spontaneous emission rate of 0.97 ns, which is the fastest single photon emission rate reported in silicon. With this radiative enhancement, we achieve an order of magnitude improvement in emitter brightness compared to previously reported values. These results pave the way for scalable quantum light sources on a silicon photonic chip.