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1. Single-Shot Readout and Weak Measurement of a Tin-Vacancy Qubit in Diamond

   https://doi.org/10.1103/PhysRevX.14.041008  

   Rosenthal, Eric I; Biswas, Souvik; Scuri, Giovanni; Lee, Hope; Stein, Abigail J; Kleidermacher, Hannah C; Grzesik, Jakob; Rugar, Alison E; Aghaeimeibodi, Shahriar; Riedel, Daniel; et al (October 2024, Physical Review X)

   The negatively charged tin-vacancy center in diamond ( ${\mathrm{SnV}}^{-}$) is an emerging platform for building the next generation of long-distance quantum networks. This is due to the ${\mathrm{SnV}}^{-}$’s favorable optical and spin properties including bright emission, insensitivity to electronic noise, and long spin coherence times at temperatures above 1 K. Here, we demonstrate measurement of a single ${\mathrm{SnV}}^{-}$electronic spin with a single-shot readout fidelity of 87.4%, which can be further improved to 98.5% by conditioning on multiple readouts. In the process, we develop understanding of the relationship between strain, magnetic field, spin readout, and microwave spin control. We show that high-fidelity readout is compatible with rapid microwave spin control, demonstrating a favorable parameter regime for use of the ${\mathrm{SnV}}^{-}$center as a high-quality spin-photon interface. Finally, we use weak quantum measurement to study measurement-induced dephasing; this illuminates the fundamental interplay between measurement and decoherence in quantum mechanics, and provides a universal method to characterize the efficiency of color-center spin readout. Taken together, these results overcome an important hurdle in the development of the ${\mathrm{SnV}}^{-}$-based quantum technologies and, in the process, develop techniques and understanding broadly applicable to the study of solid-state quantum emitters. Published by the American Physical Society2024 

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2. Narrow-Linewidth Tin-Vacancy Centers in a Diamond Waveguide

   https://doi.org/10.1021/acsphotonics.0c00833  

   Rugar, Alison E.; Dory, Constantin; Aghaeimeibodi, Shahriar; Lu, Haiyu; Sun, Shuo; Mishra, Sattwik Deb; Shen, Zhi-Xun; Melosh, Nicholas A.; Vučković, Jelena (September 2020, ACS Photonics)

   Integrating solid-state quantum emitters with photonic circuits is essential for realizing large-scale quantum photonic processors. Negatively charged tin-vacancy (SnV−) centers in diamond have emerged as promising candidates for quantum emitters because of their excellent optical and spin properties, including narrow-linewidth emission and long spin coherence times. SnV− centers need to be incorporated in optical waveguides for efficient onchip routing of the photons they generate. However, such integration has yet to be realized. In this Letter, we demonstrate the coupling of SnV− centers to a nanophotonic waveguide. We realize this device by leveraging our recently developed shallow ion implantation and growth method for the generation of high-quality SnV− centers and the advanced quasi-isotropic diamond fabrication technique. We confirm the compatibility and robustness of these techniques through successful coupling of narrow-linewidth SnV− centers (as narrow as 36 ± 2 MHz) to the diamond waveguide. Furthermore, we investigate the stability of waveguide-coupled SnV− centers under resonant excitation. Our results are an important step toward SnV−-based on-chip spin-photon interfaces, single-photon nonlinearity, and photon-mediated spin interactions. 

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3. A scalable cavity-based spin–photon interface in a photonic integrated circuit

   https://doi.org/10.1364/OPTICAQ.509233  

   Chen, Kevin_C; Christen, Ian; Raniwala, Hamza; Colangelo, Marco; De_Santis, Lorenzo; Shtyrkova, Katia; Starling, David; Murphy, Ryan; Li, Linsen; Berggren, Karl; et al (April 2024, Optica Quantum)

   A central challenge in quantum networking is transferring quantum states between different physical modalities, such as between flying photonic qubits and stationary quantum memories. One implementation entails using spin–photon interfaces that combine solid-state spin qubits, such as color centers in diamond, with photonic nanostructures. However, while high-fidelity spin–photon interactions have been demonstrated on isolated devices, building practical quantum repeaters requires scaling to large numbers of interfaces yet to be realized. Here, we demonstrate integration of nanophotonic cavities containing tin-vacancy (SnV) centers in a photonic integrated circuit (PIC). Out of a six-channel quantum microchiplet (QMC), we find four coupled SnV-cavity devices with an average Purcell factor of ∼7. Based on system analyses and numerical simulations, we find with near-term improvements this multiplexed architecture can enable high-fidelity quantum state transfer, paving the way toward building large-scale quantum repeaters. 

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4. Deterministic creation of strained color centers in nanostructures via high-stress thin films

   https://doi.org/10.1063/5.0171558  

   Assumpcao, D R; Jin, C; Sutula, M; Ding, S W; Pham, P; Knaut, C M; Bhaskar, M K; Panday, A; Day, A M; Renaud, D; et al (December 2023, Applied Physics Letters)

   Color centers have emerged as a leading qubit candidate for realizing hybrid spin-photon quantum information technology. One major limitation of the platform, however, is that the characteristics of individual color centers are often strain dependent. As an illustrative case, the silicon-vacancy center in diamond typically requires millikelvin temperatures in order to achieve long coherence properties, but strained silicon-vacancy centers have been shown to operate at temperatures beyond 1 K without phonon-mediated decoherence. In this work, we combine high-stress silicon-nitride thin films with diamond nanostructures to reproducibly create statically strained silicon-vacancy color centers (mean ground state splitting of 608 GHz) with strain magnitudes of ∼4×10−4. Based on modeling, this strain should be sufficient to allow for operation of a majority silicon-vacancy centers within the measured sample at elevated temperatures (1.5 K) without any degradation of their spin properties. This method offers a scalable approach to fabricate high-temperature operation quantum memories. Beyond silicon-vacancy centers, this method is sufficiently general that it can be easily extended to other platforms as well. 

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5. Field programmable spin arrays for scalable quantum repeaters

   https://doi.org/10.1038/s41467-023-36098-8  

   Wang, Hanfeng; Trusheim, Matthew E.; Kim, Laura; Raniwala, Hamza; Englund, Dirk R. (December 2023, Nature Communications)

   Abstract The large scale control over thousands of quantum emitters desired by quantum network technology is limited by the power consumption and cross-talk inherent in current microwave techniques. Here we propose a quantum repeater architecture based on densely-packed diamond color centers (CCs) in a programmable electrode array, with quantum gates driven by electric or strain fields. This ‘field programmable spin array’ (FPSA) enables high-speed spin control of individual CCs with low cross-talk and power dissipation. Integrated in a slow-light waveguide for efficient optical coupling, the FPSA serves as a quantum interface for optically-mediated entanglement. We evaluate the performance of the FPSA architecture in comparison to a routing-tree design and show an increased entanglement generation rate scaling into the thousand-qubit regime. Our results enable high fidelity control of dense quantum emitter arrays for scalable networking. 

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