Entanglement Enhancement in Multimode Integrated Circuits

TL;DR

This paper explores how multimode integrated circuits with multiple squeezed input states can enhance entanglement through photon subtraction, showing increased entanglement sensitivity and practical feasibility with current technology.

Contribution

It extends entanglement enhancement protocols to multimode integrated circuits, demonstrating increased entanglement with multiple squeezed inputs and analyzing optimal mode numbers.

Findings

Entanglement gain is maximized with a small number of modes, around four.

Multiple squeezed inputs improve entanglement sensitivity.

The scheme is feasible with current integrated optics technology.

Abstract

The faithful distribution of entanglement in continuous variable systems is essential to many quantum information protocols. As such, entanglement distillation and enhancement schemes are a cornerstone of many applications. The photon subtraction scheme offers enhancement with a relatively simple setup and has been studied in various scenarios. Motivated by recent advances in integrated optics, particularly the ability to build stable multimode interferometers with squeezed input states, a multimodal extension to the enhancement via photon subtraction protocol is studied. States generated with multiple squeezed input states, rather than a single input source, are shown to be more sensitive to the enhancement protocol, leading to increased entanglement at the output. Numerical results show the gain in entanglement is not monotonic with the number of modes or the degree of squeezing in the additional modes. Consequently, the advantage due to having multiple squeezed inputs states can be maximized when the number of modes is still relatively small (e.g., $4$). The requirement for additional squeezing is within the current realm of implementation, making this scheme achievable with present technologies.