Room-temperature single photon emitters based on silicon-vacancy centers in diamond nanocrystals

Abstract

Single-photon sources with well-defined spectral properties are of special interest to applications in quantum cryptography, quantum computation and quantum metrology. Silicon-vacancy (SiV) color centers in diamond nanocrystals are especially promising single photon sources due to their narrow emission bandwidth down to 0.7 nm and the high emission rate up to several Mcps into the zero-phonon-line (ZPL) at room temperature [1]. To further enhance the single photon emission rate and the spectral linewidth, SiV centers can be coupled to optical systems such as dielectric antennas [2] or fiber based micro-cavities [3]. Both these approaches require nanodiamonds with sizes < 100 nm to minimize scattering losses and good crystal quality, i.e. low strain, to preserve the advantageous optical properties of the SiV center. One possible approach to produce SiV centers in nanodiamonds is to exploit chemical vapor deposition (CVD), employing in situ incorporation of Si and stop the process when the desired size of the diamond crystals is reached [4]. Even though this method yields excellent spectral properties, relocating the nanodiamonds from the substrate is challenging.

Here we report a technique to produce SiV centers in nanodiamonds exploiting a wet-milling process to produce nanodiamonds containing single SiV centers [5, 6]. The starting material was a polycrystalline diamond film [7] directly grown by a CVD process on a silicon substrate. Plasma enhanced CVD with a 1% methane gas mixture and a sacrificial silicone source in the chamber was used to grow on purified 5 nm nanodiamond seeds (Plasmachem). The film was crushed to crystals with an average size of 50 nm, 70 nm and 100 nm (Fig. 1a), through a wet-milling process in a vibration mill with steel beads. The high amount of steel containment was removed with an extensive acid treatment. After consecutive steps of annealing and oxidizing the nanodiamonds to remove residual surface contamination, the observed zero-phonon-lines include linewidths as narrow as 0.95 nm (Fig. 1b). The center wavelengths of the zero-phonon-lines vary among SiV centers in distinct nanodiamonds, resulting in an overall distribution accumulating at approximately 740 nm. Most SiV centers exhibit ZPL linewidths of 1-2 nm, only ZPLs of a center wavelength around 740 nm display broader linewidths (Fig. 1c). Some of the nanodiamonds contain single SiV centers as proven by photon correlation measurements. Therefore, they are favorable candidates for the integration in optical systems like fiber microcavities.