Teleportation-based filtering for gravitational-wave detectors

Employing the principle of quantum teleportation in gravitational-wave detectors provides a method to address technical challenges associated with implementing quantum filters for squeezed-light injection. A recent proposal [Phys. Rev. A 110, 022601] has shown that an arbitrary number of effective squeezing-angle rotations can be achieved by cascading quantum teleportation, yielding sensitivity equivalent to frequency-dependent prefiltering. A natural question is whether the teleportation-based protocol can also realize frequency-dependent postfiltering. In this work, we examine this possibility and show that, with perfect teleportation fidelity, postfiltering can be fully implemented. In practice, however, various imperfections make the sensitivity nearly equivalent to that of teleportation-based prefiltering. We apply this scheme to the low-frequency detector in the Einstein Telescope xylophone configuration and find that teleportation-based postfiltering could also be a candidate for the detector's design.