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1. Atomic fluorescence collection into planar photonic devices

   https://doi.org/10.1364/OPTICAQ.540626  

   Smedley, Orion; Natarajan, Vighnesh; Jaramillo, Oscar; Rivy, Hamim_Mahmud; Mehta, Karan_K (January 2025, Optica Quantum)

   Fluorescence collection from individual emitters plays a key role in state detection and remote entanglement generation, fundamental functionalities in many quantum platforms. Planar photonics have been demonstrated for robust and scalable addressing of trapped-ion systems, motivating consideration of similar elements for the complementary challenge of photon collection. Here, using an argument from the reciprocity principle, we show that far-field photon collection efficiency can be simply expressed in terms of the fields associated with the collection optic at the emitter position alone. We calculate collection efficiencies into ideal paraxial and fully vectorial focused Gaussian modes parameterized in terms of focal waist, and further quantify the modest enhancements possible with more general beam profiles, establishing design requirements for efficient collection. Toward practical implementation, we design, fabricate, and characterize two diffractive collection elements operating atλ = 397 nm; a forward emitting design is predicted to offer 0.25% collection efficiency into a single waveguide mode, while a more efficient reverse-emitting design offers 1.14% collection efficiency, albeit with more demanding fabrication requirements. Close agreement between simulated and measured emission for both designs indicates practicality of these collection efficiencies, and we indicate avenues to improved devices approaching the limits predicted for ideal beams. We point out a particularly simple integrated waveguide configuration for polarization-based remote entanglement generation enabled by integrated collection. 

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2. Inverse-designed photon extractors for optically addressable defect qubits

   https://doi.org/10.1364/OPTICA.408611  

   Chakravarthi, Srivatsa; Chao, Pengning; Pederson, Christian; Molesky, Sean; Ivanov, Andrew; Hestroffer, Karine; Hatami, Fariba; Rodriguez, Alejandro_W; Fu, Kai-Mei_C (December 2020, Optica)

   Solid-state defect qubit systems with spin-photon interfaces show great promise for quantum information and metrology applications. Photon collection efficiency, however, presents a major challenge for defect qubits in high refractive index host materials. Inverse-design optimization of photonic devices enables unprecedented flexibility in tailoring critical parameters of a spin-photon interface including spectral response, photon polarization, and collection mode. Further, the design process can incorporate additional constraints, such as fabrication tolerance and material processing limitations. Here, we design and demonstrate a compact hybrid gallium phosphide on diamond inverse-design planar dielectric structure coupled to single near-surface nitrogen-vacancy centers formed by implantation and annealing. We observe up to a 14-fold broadband enhancement in photon extraction efficiency, in close agreement with simulations. We expect that such inverse-designed devices will enable realization of scalable arrays of single-photon emitters, rapid characterization of new quantum emitters, efficient sensing, and heralded entanglement schemes. 

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3. 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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4. Mm-Wave Beam Steering Antennas Using Stacked Parallel Plate Lens Antenna Subarrays

   https://doi.org/10.1109/USNC-URSI52151.2023.10237493  

   Jebreil, Omar; Mumcu, Gokhan (July 2023, IEEE)

   A millimeter (mm)-wave beam steering antenna consisting of subarrays of parallel plate lenses is presented for the first time. As compared to a previously reported antenna that utilized subarrays of dielectric slab waveguide lenses, the presented antenna allows to design and control the beamwidth of the radiation pattern in the plane orthogonal to the beam steering plane by stacking the parallel plate lens subarrays. Additionally, full wave simulations of the presented antenna show performance improvements in gain, side lobe level, and field of view in comparison to the previously reported dielectric slab waveguide-based realization. 

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5. A planar cloverleaf antenna for circularly polarized microwave fields in atomic and molecular physics experiments

   https://doi.org/10.1063/5.0167572  

   Yuan, Weijun; Zhang, Siwei; Bigagli, Niccolò; Warner, Claire; Stevenson, Ian; Will, Sebastian (December 2023, Review of Scientific Instruments)

   We report on the design and characterization of a compact microwave antenna for atomic and molecular physics experiments. The antenna is comprised of four loop antennas arranged in a cloverleaf shape, allowing for precise adjustment of polarization by tuning the relative phase of the loops. We optimize the antenna for left-circularly polarized microwaves at 3.5 GHz and characterize its near-field performance using ultracold NaCs molecules as a precise quantum sensor. Observing an unusually high Rabi frequency of 2π × 46.1(2) MHz, we extract an electric field amplitude of 33(2) V/cm at 22 mm distance from the antenna. The polarization ellipticity is 2.3(4)°, corresponding to a 24 dB suppression of right-circular polarization. The cloverleaf antenna is planar and provides large optical access, making it highly suitable for quantum control of atoms and molecules and potentially other quantum systems that operate in the microwave regime. 

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