Quantum transduction via generalized continuous-variable teleportation

Quantum transduction converts quantum states between different frequencies. Similarly, quantum teleportation transfers quantum states between different systems. While often appreciated for quantum communication between distant locations, teleportation can also operate between different frequencies. In terms of bosonic modes, quantum teleportation relies on two-mode squeezing -- squeezed on the balanced Einstein-Podolsky-Rosen (EPR) quadratures -- for entanglement and a balanced beamsplitter plus homodyne detection for Bell measurement. Since cross-frequency band entanglement is challenging to generate, we propose to enable transduction with teleportation, while only relying on a conventional transduction device and narrow-band entanglement. Our insight is that a transduction device performs a cross-frequency-band beamsplitter, almost what is needed in a Bell measurement, except that it is often not balanced. We resolve the issue by proposing a generalized teleportation protocol with arbitrarily unbalanced EPR quadratures and matched unbalanced beamsplitters. The protocol can enhance quantum transduction, using only off-the-shelf components -- intraband beamsplitters, offline squeezing, homodyne detection and displacements. The proposed protocol achieves perfect transduction when applying to a transduction device with an arbitrarily low efficiency, at infinite squeezing. A minimum squeezing in the range of [1.195,4.343] decibels is needed to achieve quantum capacity enhancement.