arXiv subjects

Julian M. Bopp

Publications and source records attributed to Julian M. Bopp.

6 recordsLinked to original sources

arXiv2025

Waveguide-integrated colour centres in silicon carbide with broadband photonic crystal reflectors for efficient readout

Spin-active colour centres in 4H silicon carbide are promising candidates as building blocks for quantum information applications. To increase the photon count rate of the emitters at low temperatures, the colour centres must be integrated into nanophotonic structures and characterised under cryogenic conditions. Here, we design and fabricate waveguide structures attached with an efficient Dinosaur photonic crystal reflector at one side. The devices show broadband reflection over a range of 60 THz with a peak reflectance above 80 %. Additionally, colour centres were integrated into these structures and characterised at cryogenic conditions. The emission was collected by a tapered-waveguide-tapered-fibre interface. Although the spectral stability of the emitters must be further improved for high excitation powers, the saturation intensity in standard PLE measurements is about 104 kcps. The count rate can be further improved to about 125 kcps with a charge-resonance check measurement scheme. To highlight the relevance of our devices, we theoretically show that these count rates enable optical single-shot readout with a fidelity exceeding 98 %.

quant-ph↗

arXiv2025

Dinosaur Photonic Crystal Cavity Interfaces for Color Center Coupling to Triangular Nanostructures

Waveguide-coupled photonic crystal cavities with a triangular cross section fabricated by angled etching are suitable to interface embedded color centers with flying photonic qubits in quantum information applications. Moreover, their fabrication requires fewer processing steps compared to nanostructures produced by quasi-isotropic undercutting. As an alternative to established hole-based photonic crystal cavities, we introduce corrugated triangular 'Dinosaur' photonic crystal cavities, and develop a tapered, quasi loss-free cavity-waveguide interface to adiabatically interconvert Bloch and waveguide modes. We optimize the cavity-waveguide interface to minimize photon losses and demonstrate that its adjustment allows precise tuning of the light-matter interaction.

physics.optics↗

arXiv2023

Coherent microwave, optical, and mechanical quantum control of spin qubits in diamond

Diamond has emerged as a highly promising platform for quantum network applications. Color centers in diamond fulfill the fundamental requirements for quantum nodes: they constitute optically accessible quantum systems with long-lived spin qubits. Furthermore, they provide access to a quantum register of electronic and nuclear spin qubits and they mediate entanglement between spins and photons. All these operations require coherent control of the color center's spin state. This review provides a comprehensive overview of the state-of-the-art, challenges, and prospects of such schemes, including, high fidelity initialization, coherent manipulation, and readout of spin states. Established microwave and optical control techniques are reviewed, and moreover, emerging methods such as cavity-mediated spin-photon interactions and mechanical control based on spin-phonon interactions are summarized. For different types of color centers, namely, nitrogen-vacancy and group-IV color centers, distinct challenges persist that are subject of ongoing research. Beyond fundamental coherent spin qubit control techniques, advanced demonstrations in quantum network applications are outlined, for example, the integration of individual color centers for accessing (nuclear) multi-qubit registers. Finally, we describe the role of diamond spin qubits in the realization of future quantum information applications.

quant-ph↗

arXiv2023

Diamond-on-chip infrared absorption magnetic field camera

Integrated and fiber-packaged magnetic field sensors with a sensitivity sufficient to sense electric pulses propagating along nerves in life science applications and with a spatial resolution fine enough to resolve their propagation directions will trigger a tremendous step ahead not only in medical diagnostics, but in understanding neural processes. Nitrogen-vacancy centers in diamond represent the leading platform for such sensing tasks under ambient conditions. Current research on uniting a good sensitivity and a high spatial resolution is facilitated by scanning or imaging techniques. However, these techniques employ moving parts or bulky microscope setups. Despite being far developed, both approaches cannot be integrated and fiber-packaged to build a robust, adjustment-free hand-held device. In this work, we introduce novel concepts for spatially resolved magnetic field sensing and 2-D gradiometry with an integrated magnetic field camera. The camera is based on infrared absorption optically detected magnetic resonance (IRA-ODMR) mediated by perpendicularly intersecting infrared and pump laser beams forming a pixel matrix. We demonstrate our 3-by-3 pixel sensor's capability to reconstruct the position of an electromagnet in space. Furthermore, we identify routes to enhance the magnetic field camera's sensitivity and spatial resolution as required for complex sensing applications.

physics.app-ph↗

arXiv2023

Fabrication of Sawfish photonic crystal cavities in bulk diamond

Color centers in diamond are quantum systems with optically active spin-states that show long coherence times and are therefore a promising candidate for the development of efficient spin-photon interfaces. However, only a small portion of the emitted photons is generated by the coherent optical transition of the zero-phonon line (ZPL), which limits the overall performance of the system. Embedding these emitters in photonic crystal cavities improves the coupling to the ZPL photons and increases their emission rate. Here, we demonstrate the fabrication process of "Sawfish" cavities, a design recently proposed that has the experimentally-realistic potential to simultaneously enhance the emission rate by a factor of 46 and couple photons into a single-mode fiber with an efficiency of 88%. The presented process allows for the fabrication of fully suspended devices with a total length of 20.5 $μ$m and features size as small as 40 nm. The optical characterization shows fundamental mode resonances that follow the behavior expected from the corresponding design parameters and quality (Q) factors as high as 3825. Finally, we investigate the effects of nanofabrication on the devices and show that, despite a noticeable erosion of the fine features, the measured cavity resonances deviate by only 0.9 (1.2)% from the corresponding simulated values. This proves that the Sawfish design is robust against fabrication imperfections, which makes it an attractive choice for the development of quantum photonic networks.

physics.optics↗

arXiv2022

'Sawfish' Photonic Crystal Cavity for Near-Unity Emitter-to-Fiber Interfacing in Quantum Network Applications

Photon loss is one of the key challenges to overcome in complex photonic quantum applications. Photon collection efficiencies directly impact the amount of resources required for measurement-based quantum computation and communication networks. Promising resources include solid-state quantum light sources, however, efficiently coupling light from a single quantum emitter to a guided mode remains demanding. In this work, we eliminate photon losses by maximizing coupling efficiencies in an emitter-to-fiber interface. We develop a waveguide-integrated 'Sawfish' photonic crystal cavity and use finite element simulations to demonstrate that our system transfers, with 97.4% efficiency, the zero-phonon line emission of a negatively-charged tin vacancy center in diamond adiabatically to a single-mode fiber. A surrogate model trained by machine learning provides quantitative estimates of sensitivities to fabrication tolerances. Our corrugation-based design proves robust under state-of-the-art nanofabrication parameters, maintaining an emitter-to-fiber coupling efficiency of 88.6%. To demonstrate its potential in reducing resource requirements, we apply the Sawfish cavity to a recent one-way quantum repeater protocol.

quant-ph↗