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1. Triangular cross-section beam splitters in silicon carbide for quantum information processing

   https://doi.org/10.1557/s43579-024-00557-0  

   Majety, Sridhar; Saha, Pranta; Kekula, Zbynka; Dhuey, Scott; Radulaski, Marina (May 2024, MRS Communications)

   Abstract Triangular cross-section color center photonics in silicon carbide is a leading candidate for scalable implementation of quantum hardware. Within this geometry, we model low-loss beam splitters for applications in key quantum optical operations such as entanglement and single-photon interferometry. We consider triangular cross-section single-mode waveguides for the design of a directional coupler. We optimize parameters for a 50:50 beam splitter. Finally, we test the experimental feasibility of the designs by fabricating triangular waveguides in an ion beam etching process and identify suitable designs for short-term implementation. 

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2. Universal interference-based construction of Gaussian operations in hybrid quantum systems

   https://doi.org/10.1038/s41534-022-00581-9  

   Zhang, Mengzhen; Chowdhury, Shoumik; Jiang, Liang (June 2022, npj Quantum Information)

   Abstract Beam-splitter operations are an indispensable resource for processing quantum information encoded in bosonic modes. In hybrid quantum systems, however, it can be challenging to implement reliable beam-splitters between two distinct modes due to various experimental imperfections. Without beam-splitters, realizing arbitrary Gaussian operations between bosonic modes can become highly non-trivial or even infeasible. In this work, we develop interference-based protocols for engineering Gaussian operations in multi-mode hybrid bosonic systems without requiring beam-splitters. Specifically, for a given generic multi-mode Gaussian unitary coupler, we demonstrate a universal scheme for constructing Gaussian operations on a desired subset of the modes, requiring only multiple uses of the given coupler interleaved with single-mode Gaussian unitaries. Our results provide efficient construction of operations crucial to quantum information science, and are derived from fundamental physical properties of bosonic systems. The proposed scheme is thus widely applicable to existing platforms and couplers, with the exception of certain edge cases. We introduce a systematic approach to identify and treat these edge cases by utilizing an intrinsically invariant structure associated with our interference-based construction. 

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3. Topological Qubits as Carriers of Quantum Information in Optics

   https://doi.org/10.3390/app9030575  

   Jaeger, Gregg; Simon, David; Sergienko, Alexander (February 2019, Applied Sciences)

   Winding number is a topologically significant quantity that has found valuable applications in various areas of mathematical physics. Here, topological qubits are shown capable of formation from winding number superpositions and so of being used in the communication of quantum information in linear optical systems, the most common realm for quantum communication. In particular, it is shown that winding number qubits appear in several aspects of such systems, including quantum electromagnetic states of spin, momentum, orbital angular momentum, polarization of beams of particles propagating in free-space, optical fiber, beam splitters, and optical multiports. 

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4. Integrated visible-light polarization rotators and splitters for atomic quantum systems

   https://doi.org/10.1364/OL.509747  

   Hattori, Ashton; Sneh, Tal; Notaros, Milica; Corsetti, Sabrina; Callahan, Patrick_T; Kharas, Dave; Mahony, Thomas; McConnell, Robert; Chiaverini, John; Notaros, Jelena (March 2024, Optics Letters)

   In this work, we design and experimentally demonstrate the first, to the best of our knowledge, integrated polarization splitters and rotators at blue wavelengths. We develop compact and efficient designs for both a polarization splitter and rotator at a 422-nm wavelength, an important laser-cooling transition for⁸⁸Sr⁺ions. These devices are fabricated in a 200-mm wafer-scale process and experimentally demonstrated, resulting in a measured polarization-splitter transverse-electric thru-port coupling of 98.0% and transverse-magnetic tap-port coupling of 77.6% for a compact 16-µm-long device and a polarization-rotator conversion efficiency of 92.2% for a separate compact 111-µm-long device. This work paves the way for more sophisticated integrated control of trapped-ion and neutral-atom quantum systems. 

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5. Scientific Computing with Diffractive Optical Neural Networks

   https://doi.org/10.1002/aisy.202300536  

   Chen, Ruiyang; Tang, Yingheng; Ma, Jianzhu; Gao, Weilu (October 2023, Advanced Intelligent Systems)

   Diffractive optical neural networks (DONNs) are emerging as high‐throughput and energy‐efficient hardware platforms to perform all‐optical machine learning (ML) in machine vision systems. However, the current demonstrated applications of DONNs are largely image classification tasks, which undermine the prospect of developing and utilizing such hardware for other ML applications. Herein, the deployment of an all‐optical reconfigurable DONNs system for scientific computing is demonstrated numerically and experimentally, including guiding two‐dimensional quantum material synthesis, predicting the properties of two‐dimensional quantum materials and small molecular cancer drugs, predicting the device response of nanopatterned integrated photonic power splitters, and the dynamic stabilization of an inverted pendulum with reinforcement learning. Despite a large variety of input data structures, a universal feature engineering approach is developed to convert categorical input features to images that can be processed in the DONNs system. The results open up new opportunities for employing DONNs systems for a broad range of ML applications. 

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