  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 a Bell-state analyzer on a
reconfigurable platform that can herald high fidelity entanglement between
ions. In this work, we design a photonic Bell-state analyzer on a
reconfigurable thin film lithium niobate platform for polarization-encoded
qubits. We optimize the device to achieve high fidelity entanglement between
two trapped ions and find >99% fidelity. The proposed device 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.
