Integrated scheme for transferring quantum entanglement via backward acousto-optic polarization conversion in a thin-film lithium niobate resonator

We present a numerical study of the design of a microwave-to-optical quantum converter based on Brillouin backscattering in a single thin-film lithium niobate racetrack resonator. The conversion involves TE0 to TM0 polarization conversion mediated by an even-parity acoustic mode that can be excited by a conventional symmetric interdigital transducer. Co-localization of the optical and acoustic fields within a single resonator enhances their interaction, while the signal is separated from the strong optical pump by propagation direction, polarization, and frequency. Combining full-vector electromagnetic and acoustic calculations with a pulsed entanglement transfer protocol, we obtain a vacuum coupling of g0/2π = 2 kHz for the designed perimeter and show that cooperativity of C = 1 is achieved with a calculated on-chip pump power of approximately 2.94 μW for Qopt = 107 and Qac = 105. Under these assumptions, the protocol enables entanglement transfer from a superconducting qubit to a flying telecom photon, supporting the proposed architecture as a compact platform for integrated quantum transduction.