An Integrated Bell-State Analyzer on a Thin Film Lithium Niobate Platform

Trapped ions are excellent candidates for quantum computing and quantum networks because of their long coherence times, ability to generate entangled photons as well as high fidelity single- and two-qubit gates. To scale up trapped-ion quantum computing, we need to develop a Bell-state analyzer on a reconfigurable platform that can herald high fidelity entanglement between remote ions. Thin-film lithium niobate is an attractive platform for its large transparency window and high electro-optic coefficient. However, trapped ions naturally emit polarization-encoded photonic qubits, while thin-film lithium niobate devices are polarization-sensitive due to the large mode anisotropy created during fabrication. In this work, we design a photonic Bell-state analyzer on a thin film lithium niobate platform for polarization-encoded qubits. We optimize the dimensions of the bell state analyzer and input coupler to achieve polarization-insensitive operation. We achieve high fidelity entanglement between two trapped ions and determine > 99.99% fidelity in the final optimized device. The proposed Bell-state analyzer can scale up trapped ion quantum computing as well as other optically active spin qubits, such as color centers in diamond, quantum dots, and rare-earth ions.