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Quantum information with optical centers in diamond films

Subject Area Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
Term from 2006 to 2011
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 24204133
 
Final Report Year 2012

Final Report Abstract

1) Bright single photon emitters: We have demonstrated a novel solid-state single photon emitter with unique properties: To this end, we have produced single Silicon-Vacancy (SiV) color centers using a novel material system consisting of nano-diamonds of approximately 150 nm size grown by a Chemical Vapor Deposition process on an iridium film. The color centers exhibit extraordinary narrow electronic transitions (zero-phonon lines, ZPL) down to 0.7 nm at room temperature with a fraction of up to 88 % of photons emitted into the ZPL. Single photon count rates above 5 Mcps at saturation make these SiV centers the brightest diamond-based single photon sources to date. The emission is found to be linearly polarized to a high degree. The much improved spectral properties (e.g. small linewidth, high count rates) as compared to earlier works are attributed to the high crystalline quality and low impurity content of the nano-diamonds as well as to the high collection efficiency from the iridium surface. Thus, the SiV color centers observed were proven to be much better than their reputation. Furthermore, the advanced material system for the first time allowed for detailed spectroscopy of single SiV centers. Here, we have measured for the first time the fine structure of a single SiV center at cryogenic temperatures, thus confirming its atomic composition. Polarization measurements of single SiV centers surprisingly show evidence for orientation of the center's dipole along h110i direction which is contradictory to current theoretical models for the SiV center. Another novel result is the detection of a narrow line within the region of the sideband spectrum around 825 nm which has been identified as a second electronic transition by temperature-dependent spectroscopy and photon cross-correlation measurements. Further spectroscopic investigations will be necessary to clarify the symmetry and the internal level structure of the SiV center. 2) Photonic crystal microcavities: Using a very similar material system, i.e. a thin, single-crystal diamond film on iridium, we were able to demonstrate for the first time photonic crystal cavities in single crystal diamond. The fabrication process combines production of a free standing diamond membrane of 300 nm thickness and milling of the photonic crystal structure into the diamond film by a focused ion beam. The resulting one- and two-dimensional microcavities feature quality factors in the range 500 … 700 currently limited by fabrication imperfections. The diamond film contains a large ensemble of SiV centers which can be coupled to the photonic crystal cavity modes. In order to actively tune the cavity modes we have developed a digital etching technique: By successively oxidizing the diamond membrane the cavity modes are blue-tuned by 3 nm on average per oxidation step. Using this oxidation method, we tune a mode of the 2D cavity into resonance with the ZPL of an ensemble of SiV centers. On resonance, we see a clear enhancement of the intensity by a factor of 2.8 compared to the off resonant spectrum resulting from a spectrally resolved Purcell enhancement of the SiV centers' spontaneous emission. Further investigations will focus on improvement of the quality factors by optimized fabrication processes and deterministic coupling of single color centers to the cavities.

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