Carsten Arend

Narrowband fluorescent nanodiamonds produced from chemical vapor deposition films

We report on the production of nanodiamonds (NDs) with 70–80 nm size via bead assisted sonic disintegration (BASD) of a polycrystalline chemical vapor deposition film. The high crystalline quality NDs display intense narrowband (7 nm) room temperature luminescence at 738 nm from in situ incorporated silicon vacancy centers. We demonstrate bright, narrowband single photon emission with >100 000 cps. Due to the narrow fluorescence bandwidth as well as the near-infrared emission these NDs are also suitable as fluorescence labels with significantly enhanced performance for in vivo imaging.

Deterministic Coupling of a Single Silicon-Vacancy Color Center to a Photonic Crystal Cavity in Diamond

Deterministic coupling of single solid-state emitters to nanocavities is the key for integrated quantum information devices. We here fabricate a photonic crystal cavity around a preselected single silicon-vacancy color center in diamond and demonstrate modification of the emitters internal population dynamics and radiative quantum efficiency. The controlled, room-temperature cavity coupling gives rise to a resonant Purcell enhancement of the zero-phonon transition by a factor of 19, coming along with a 2.5-fold reduction of the emitters lifetime.

All-optical formation of coherent dark states of silicon-vacancy spins in diamond

Spin impurities in diamond can be versatile tools for a wide range of solid-state-based quantum technologies, but finding spin impurities that offer sufficient quality in both photonic and spin properties remains a challenge for this pursuit. The silicon-vacancy center has recently attracted much interest because of its spin-accessible optical transitions and the quality of its optical spectrum. Complementing these properties, spin coherence is essential for the suitability of this center as a spin-photon quantum interface. Here, we report all-optical generation of coherent superpositions of spin states in the ground state of a negatively charged silicon-vacancy center using coherent population trapping. Our measurements reveal a characteristic spin coherence time, T2*, exceeding 45 nanoseconds at 4 K. We further investigate the role of phonon-mediated coupling between orbital states as a source of irreversible decoherence. Our results indicate the feasibility of all-optical coherent control of silicon-vacancy spins using ultrafast laser pulses.

Evaluation of nitrogen- and silicon-vacancy defect centres as single photon sources in quantum key distribution

We demonstrate a quantum key distribution (QKD) testbed for room temperature single photon sources based on defect centres in diamond. A BB84 protocol over a short free-space transmission line is implemented. The performance of nitrogen-vacancy (NV) as well as silicon-vacancy defect (SiV) centres is evaluated. An extrapolation for the future applicability of such sources in quantum information processing is discussed.

Ultrafast all-optical coherent control of silicon vacancy colour centres in diamond

Complete control of the state of a quantum bit (qubit) is a fundamental requirement for any quantum information processing (QIP) system. In this context, all-optical control techniques offer the advantage of a well-localized and potentially ultrafast manipulation of individual qubits in multi-qubit systems. Recently, the negatively charged silicon vacancy centre (SiV−) in diamond has emerged as a novel promising system for QIP due to its superior spectral properties and advantageous electronic structure, offering an optically accessible Λ-type level system with large orbital splittings. Here, we report on all-optical resonant as well as Raman-based coherent control of a single SiV− using ultrafast pulses as short as 1 ps, significantly faster than the centres phonon-limited ground state coherence time of about 40 ns. These measurements prove the accessibility of a complete set of single-qubit operations relying solely on optical fields and pave the way for high-speed QIP applications using SiV− centres.

Low temperature investigations and surface treatments of colloidal narrowband fluorescent nanodiamonds

We report fluorescence investigations and Raman spectroscopy on colloidal nanodiamonds (NDs) obtained via bead assisted sonic disintegration (BASD) of a polycrystalline chemical vapor deposition film. The BASD NDs contain in situ created silicon vacancy (SiV) centers. Whereas many NDs exhibit emission from SiV ensembles, we also identify NDs featuring predominant emission from a single bright SiV center. We demonstrate oxidation of the NDs in air as a tool to optimize the crystalline quality of the NDs via removing damaged regions resulting in a reduced ensemble linewidth as well as single photon emission with increased purity. We furthermore investigate the temperature dependent zero-phonon-line fine-structure of a bright single SiV center as well as the polarization properties of its emission and absorption.

Photoluminescence excitation and spectral hole burning spectroscopy of silicon vacancy centers in diamond

Silicon-vacancy (SiV) centers in diamond are promising systems for quantum information applications due to their bright single-photon emission and optically accessible spin states. Furthermore, SiV centers in low-strain diamond are insensitive to perturbations of the dielectric environment; i.e., they show very weak spectral diffusion. This property renders ensembles of SiV centers interesting for sensing applications. We here report on photoluminescence excitation (PLE) spectroscopy on an SiV ensemble in a low strain, chemical vapor deposition-grown high-quality diamond layer, where we measure the fine structure with high resolution and obtain the line widths and splittings of the SiV centers. We investigate the temperature dependence of the width and position of the fine structure peaks. Our measurements reveal line widths of about 10 GHz as compared to a lifetime limited width on the order of 0.1 GHz. This difference arises from the inhomogeneous broadening of the transitions caused by residual strain. To overcome inhomogeneous broadening we use spectral hole burning spectroscopy, which enables us to measure a nearly lifetime limited homogeneous line width of 279 MHz. Furthermore, we demonstrate evidence of coherent interaction in the system by driving a

Low-noise quantum frequency down-conversion of indistinguishable photons

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Site selective growth of heteroepitaxial diamond nanoislands containing single SiV centers

scheme. Additional measurements on single emitters created by ion implantation confirm the homogeneous line widths seen in the spectral hole burning experiments and relate the ground-state splitting to the decoherence rate.

Low-noise quantum frequency down-conversion of indistinguishable photons(Conference Presentation)

We present experimental results on quantum frequency down-conversion of indistinguishable single photons emitted by an InAs/GaAs quantum dot at 904 nm to the telecom C-band at 1557 nm. Hong-Ou-Mandel (HOM) interference measurements are shown prior to and after the down-conversion step. We perform Monte-Carlo simulations of the HOM experiments taking into account the time delays of the different interferometers used and the signal-to-background ratio and further estimate the impact of spectral diffusion on the degree of indistinguishability. By that we conclude that the down-conversion step does not introduce any loss of HOM interference visibility. A noise-free conversion-process along with a high conversion-efficiency (> 30 %) emphasize that our scheme is a promising candidate for an efficient source of indistinguishable single photons at telecom wavelengths.