Novel Single Photon Emitters Based on Color Centers in Diamond

Abstract

Exploitation of emerging quantum technologies requires efficient fabrication of key building blocks. Single photon sources are one of these fundamental constituents that are presently pushing the bounds of existing materials and fabrication techniques. Color centers in diamond are very attractive in this respect since they are the only photostable solid-state single photon emitters operating at room temperature known to date.The Nitrogen-Vacancy (NV) complex is one example of such an optical center and has been subject to intensive research due to the availability of optical readout of its individual electronic spin state. However, the NV center has fundamental limitations: strong phonon coupling of the excited state which results in a broad photoluminescence spectrum (~ 100 nm) of which the zero-phonon line makes up only 4%. Emission of single photons in the zero phonon line is then extremely weak, typically on the order of a few thousands of photons per second. Such count rates are insufficient for the realization of advanced quantum information processing protocols.To move beyond the limitations of the NV there is an emerging need to identify and fabricate novel diamond based single photon emitters with improved photo-physical characteristics. Development of such emitters is the main goal of this thesis.We first concentrate on the recent progress in materials science and fabrication techniques of high quality nanodiamond crystals. We demonstrate the ability to grow high quality, submicron sized diamond crystals with a control over their final size and density using a microwave assisted chemical vapor deposition.We then study two methodologies to engineer diamond based single photon emitters in the grown nanodiamonds. In the first, nickel is implanted into the substrate onto which the nanocrystals are subsequently grown. During the diamond growth, the substrate is slightly etched and the nickel atoms diffuse and incorporate into the growing crystals. In the second we employ direct ion implantation of nickel into already deposited individual diamond nanocrystals. Optical and correlation spectroscopy measurements reveal that these methodologies are effective to fabricate nickel related single photon emitters, with zero phonon lines centered in the near infra-red and a short excited state lifetime (~3 ns).ii Furthermore, the ability of diamond to host various luminescence centers prompted the discovery of a new class of ultra bright single photon emitters. These new emitters found in diamond crystals grown on sapphire substrate and assigned to chromium, which is present in the substrate and incorporated into the crystal during the growth. Nanodiamonds hosting these centers deliver outstanding performance such as narrow photoluminescence in the near infra-red and ultra bright single photon emission with count rate of ~ 3.2×10 6 counts/s -the brightest single photon source known to date.Importantly, some of the emitters exhibit a photon statistics without any photon bunching at saturation, indicating a two-...

Diamond nanophotonics

“…Due to the large band-gap energy of 5.46 eV, it is likely that localized defect states are present in the forbidden band. Not surprisingly over 500 such “deep trap” centers are meanwhile known in diamond [15–16]. Their fluorescence emission covers a broad spectral range reaching from the UV to the far IR.…”

“…A drawback, on the other hand, is the inevitable damage caused to the diamond lattice, which leads to an additional photoluminescence (PL) background and disturbances of the photoluminescence emission [18]. Furthermore, not every color center in diamond can be produced by implantation with an adequate yield [15]. The direct synthesis of diamond crystals by microwave plasma enhanced chemical vapor deposition (MWPECVD) offers an alternative route to integrate color centers and was investigated in addition to ion implantation [19–20].…”

“…A frequently applied method is to expose a solid state source containing the dopant material directly to the reactive plasma [15,19,21]. We also used this approach for the doping of nanodiamond crystals with silicon, which will be discussed in section 5.5.…”