Low-loss telecom-band nanofiber cavity for interfacing Yb atomic qubits

We demonstrate the fabrication of an optical nanofiber cavity designed for efficient interface with ytterbium (Yb) atoms at telecom-wavelength transitions. Replacing the conventional hydrogen-oxygen flame with a deuterium-oxygen flame in the heat-and-pull method suppresses hydroxyl-induced absorption losses and enables low-loss nanofiber production with minimal modifications to the existing fabrication system. Using this technique, we fabricate a nanofiber cavity at 1389 nm that exhibits an intrinsic round-trip loss of 0.31(2)% and a finesse of 2.0(1)×10³. This performance corresponds to a projected cooperativity of 90 when interfaced with Yb atoms, indicating that the cavity is well suited for efficient atom-photon coupling at telecom-wavelength transitions. Our results establish a practical route for developing fiber-integrated atom-photon interfaces in the telecom band, a critical step toward scalable quantum communication and distributed quantum computing.