Subtraction better than addition: Entanglement in multimode squeezed vacuum post-interface with photons

TL;DR

This study compares photon-added and photon-subtracted four-mode squeezed vacuum states, revealing that photon subtraction can produce higher entanglement than addition, contrary to two-mode cases, with implications for quantum information processing.

Contribution

It demonstrates that photon subtraction enhances entanglement more effectively than addition in four-mode squeezed states, challenging previous two-mode assumptions.

Findings

Photon subtraction yields higher entanglement than addition in four-mode states.

Photon-subtracted states show greater logarithmic negativity than photon-added states.

Entanglement features are not fully captured by non-Gaussianity measures.

Abstract

We investigate the entanglement patterns of photon-added and -subtracted four-mode squeezed vacuum states. Entanglements in different scenarios are analyzed by varying the number of photons added or subtracted in certain modes, which are referred to as the "player" modes, the others being "spectators." We find that the photon-subtracted state can give us higher entanglement than the photon-added state which is in contrast of the two-mode situation. We also study the logarithmic negativity of the two-mode reduced density matrix obtained from the four-mode state which again shows that the state after photon subtraction can possess higher entanglement than that of the photon-added state, and we then compare it to that of the two-mode squeezed vacuum state. Moreover, we examine the non-Gaussianity of the photon-added and -subtracted states to find that the rich features provided by entanglement cannot be captured by the measure of non-classicality.