Color centers integrated with nanophotonic devices have emerged as a compelling platform for quantum science and technology. Here, we integrate tin-vacancy centers in a diamond waveguide and investigate the interaction with light at the single-photon level in both reflection and transmission. We observe single-emitter-induced extinction of the transmitted light up to 25% and measure the nonlinear effect on the photon statistics. Furthermore, we demonstrate fully tunable interference between the reflected single-photon field and laser light backscattered at the fiber end and show the corresponding controlled change between bunched and antibunched photon statistics in the reflected field.

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We present our optimized diamond fabrication process based on quasi-isotropic crystal-plane-dependent reactive-ion-etching at low and high temperature plasma regime. We demonstrate successful integration of SnV centers in diamond waveguides showing quantum non-linear effects. We report on our latest results on all-diamond photonic crystal cavities.

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We demonstrate heralded initialization of charge state and optical transition frequency of diamond tin-vacancy centers, using (off-)resonant lasers, photon detection and real-time logic. Using this, we show frequency tunability > 100 MHz and strongly improved optical coherence.

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We demonstrate coherent coupling of a single diamond Tin-Vacancy center to a fiber-based microcavity, showing a cavity transmission dip of 50 % on resonance, and altered photon statistics in cavity transmission.

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The generation of entanglement between distant quantum systems is at the core of quantum networking. In recent years, numerous theoretical protocols for remote-entanglement generation have been proposed, many of which have been experimentally realized. Here, we provide a modular theoretical framework to elucidate the general mechanisms of photon-mediated entanglement generation between single spins in atomic or solid-state systems. Our framework categorizes existing protocols at various levels of abstraction and allows for combining the elements of different schemes in new ways. These abstraction layers make it possible to readily compare protocols for different quantum hardware. To enable the practical evaluation of protocols tailored to specific experimental parameters, we have devised numerical simulations based on the framework with our codes available online.

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We report on the realization of a fiber-based microcavity, exhibiting low cavity length fluctuations in combination with full spatial and spectral tunability. The microcavity is used to demonstrate Purcell-enhancement of diamond Tin-Vacancy centers.@en

A large-scale quantum network, where many nodes are connected via entanglement and can share and process quantum information, will allow applications that are now unattainable. While some are known, ranging from distributed quantum computing to enhanced quantum sensing and quantum communication, the full potential of such a fundamentally new technology is yet to be discovered. Color centers in diamond, with their excellent optical properties, long spin coherence times, and versatile control over local nuclear spins, are a leading platform for building quantum network nodes and recently allowed crucial proof-of-principle experiments. Going beyond experiments and towards a large and functional network requires faster entanglement generation and a scalable architecture. Integration of color centers in nanophotonic structures paves the way to solving these challenges, enhancing the interface between the spins and photons that carry quantum information across the network. Furthermore, combining diamond nanophotonic devices with integrated photonic and electronic circuits is a promising way to realize a large-scale quantum system. This thesis is about integrated spin-photon interfaces in diamonds and how to generate entanglement between them and includes experimental and theoretical results toward this goal.

First, we introduce the Group-IV color centers in diamond, which thanks to their symmetry properties are robust against electric field noise and compatible with integration in nano-scale structures. Focusing on the tin-vacancy (SnV) center, we discuss the main features and effects that play a role in its use as a spin-photon interface. We then present experimental results going from the fabrication and characterization of bulk diamond samples with SnV centers to the integration in nanophotonic waveguides, where we show stable and coherent optical lines and measure the extinction of the transmission signal caused by a single SnV center with contrast up to 35%.

Then, we investigate the interaction between a single SnV center and a weak coherent light field in a single-mode waveguide. We perform spectroscopy of the transmitted and reflected signals, and demonstrate the single-photon nature of the interaction by measuring the effect on the photon statistics in both fields.

Finally, we introduce a theoretical framework for photon-mediated entanglement generation protocols between spin-based quantum systems. This allows us to understand, categorize, and construct entanglement protocols in terms of abstract building blocks, that can be combined with hardware modeling for a more detailed description of the protocols. To showcase the framework, we analyze three different entanglement protocols, considering silicon-vacancy (SiV) centers coupled to photonic crystal cavities as the hardware, and we quantitatively compare them using a software package built to match the structure of the framework.@en

We show diamond Tin-Vacancy centers, coherently-coupled to a tunable microcavity. The exceptional optical properties of this emitter in combination with a stable, high quality cavity enables a cavity transmission signal modulated by a single emitter.

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Diamond tin-vacancy centers have emerged as a promising platform for quantum information science and technology. A key challenge for their use in more-complex quantum experiments and scalable applications is the ability to prepare the center in the desired charge state with the optical transition at a predefined frequency. Here we report on heralding such successful preparation using a combination of laser excitation, photon detection, and real-time logic. We first show that fluorescence photon counts collected during an optimized resonant probe pulse strongly correlate with the subsequent charge state and optical-transition frequency, enabling real-time heralding of the desired state through threshold photon counting. We then implement and apply this heralding technique to photoluminescence-excitation measurements, coherent optical driving, and an optical Ramsey experiment, finding strongly increased optical coherence with increasing threshold. Finally, we demonstrate that the prepared optical frequency follows the probe laser across the inhomogeneous linewidth, enabling tuning of the transition frequency over multiple homogeneous linewidths.

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Efficient coupling of optically active qubits to optical cavities is a key challenge for solid-state-based quantum optics experiments and future quantum technologies. Here we present a quantum photonic interface based on a single tin-vacancy center in a micrometer-thin diamond membrane coupled to a tunable open microcavity. We use the full tunability of the microcavity to selectively address individual tin-vacancy centers within the cavity mode volume. Purcell enhancement of the tin-vacancy center optical transition is evidenced both by optical excited state lifetime reduction and by optical linewidth broadening. As the emitter selectively reflects the single-photon component of the incident light, the coupled emitter-cavity system exhibits strong quantum nonlinear behavior. On resonance, we observe a transmission dip of 50% for low incident photon number per Purcell-reduced excited state lifetime, while the dip disappears as the emitter is saturated with higher photon number. Moreover, we demonstrate that the emitter strongly modifies the photon statistics of the transmitted light by observing photon bunching. This work establishes a versatile and tunable platform for advanced quantum optics experiments and proof-of-principle demonstrations on quantum networking with solid-state qubits.@en

We show coupling of an SnV center to a diamond waveguide of 20% with almost transform-limited optical transitions. Besides, we show control over the SnV spin qubit and extend its coherence to over a millisecond.

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We fabricate single tin-vacancy centres in diamond, we perform spectroscopy and coherent population trapping to verify optical driving of the spin states. We investigate the integration in diamond waveguides to realise an efficient spin-photon interface.

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