Applications of quantum photonics to quantum communications and quantum simulation or computing require a scalable, compact and low-cost technology for future widespread deployment. The silicon-on-insulator (SOI) platform is highly attractive in this context, offering the possibility to implement a large panel of integrated devices for the coherent manipulation, encoding and detection of single photons. However, the lack of a source able to emit a single photon pulse on demand increases the complexity and limits the performances of quantum photonic chips.
The recent observation of photon antibunching for isolated punctual defects in implanted silicon, such as the G (See
PHELIQS highlight on Jan. 12, 2021) or the W (
Y. Baron et al, ACS Photonics. 9, 2337 2022) color center is a game changing advance. It shows that the spontaneous emission of such a color center can be used to generate one and only one photon on demand. In view of practical applications, single photons must be prepared in a well-defined quantum state. As shown for other single photon emitters such as quantum dots, this can be achieved by embedding the emitter inside an optical cavity, so as to harness quantum cavity effects and tailor spontaneous emission.
In this context, we have recently observed a strong enhancement of the zero-phonon emission of G centers embedded in SOI microrings. The microrings have been fabricated at the Upstram Nanofabrication Facility (PTA) in Grenoble, starting from a SOI wafer containing G centers, produced through carbon implantation and thermal annealing. The resonant modes of the ring show up on the photoluminescence spectra and display a Q around 3000. Through a fine tuning of the ring diameter by 5nm steps, we obtain a spectral resonance between the zero-phonon line of the G centers and one of the resonant modes of the ring. A five-fold enhancement of the zero-phonon photoluminescence (PL) signal is observed at resonance thanks to Purcell-enhancement, in agreement with theoretical estimates [1].
However, we did not observe on G centers a shortening of the photoluminescence decay time, since their relaxation is dominated by non-radiative processes and phonon-assisted emission. For this reason, the G center does not appear to be the best candidate for building a highly efficient single-photon source.
We focus now our efforts on other color centers that display a higher radiative quantum efficiency, such as the W center. Additionally, other on-going efforts aim at integrating a single color center, instead of color centers ensembles, inside SOI cavities.
Figure: Electron micrograph (a) and photoluminescence map (b) of a SOI microring containing an ensemble of G centers. (c) Photoluminescence spectra obtained for five rings of increasing diameter, in steps of 5 nm. We observe a strong enhancement of the “zero-phonon” emission line of the G centers (whose spectral position is indicated by the dashed line) when it resonates with a cavity mode (here the mode m=15, whose spectral position is marked by an arrow). This condition is satisfied for the ring R3.