Generating continuous variable entangled states for quantum teleportation using a superposition of number-conserving operations

Abstract

We investigate the states generated in continuous variable (CV) optical fields on operating them with a number-conserving operator of the type $s\hat{a}\hat{a}^†+ t\hat{a}^†\hat{a}$, formed by the generalised superposition of products of field annihilation ($\hat{a}$) and creation ($\hat{a}^†$) operators, with $s^2+t^2=1$. Such an operator is experimentally realizable and can be suitably manipulated to generate nonclassical optical states when applied on single- and two-mode coherent, thermal, and squeezed input states. At low intensities, these nonclassical states can interact with a secondary mode via a linear optical device to generate two-mode discrete entangled states, which can serve as a resource in quantum information protocols. The advantage of these operations are tested by applying the generated entangled states as quantum channels in CV quantum teleportation, under the Braunstein and Kimble protocol. We observe that, under these operations, while the average fidelity of CV teleportation is enhanced for the nonclassical channel formed using input squeezed states, it remains at the classical threshold for input coherent and thermal states. This is due to the fact that though these operations can introduce discrete entanglement in all input states, it enhances the Einstein-Podolosky-Rosen (EPR) correlations only in the nonclassical squeezed state inputs, leading to an advantage in CV teleportation. This shows that nonclassical optical states generated using the above operations on classical coherent and thermal state inputs are not resourceful for CV teleportation. This investigation could prove useful in efficient implementation of noisy non-Gaussian channels, formed by linear operations, in future teleportation protocols.