Entanglement in a linear coherent feedback chain of nondegenerate optical parametric amplifiers
For researchers in quantum optics and quantum information, this work provides an incremental extension of previous dual-NOPA results to larger chains, demonstrating improved power efficiency for entanglement generation.
This paper analyzes linear quantum networks of up to 6 nondegenerate optical parametric amplifiers (NOPAs) in a coherent feedback chain, showing that networks with more NOPAs require less total pump power to achieve the same degree of Einstein-Podolsky-Rosen (EPR) entanglement in the absence of losses and delays, and reports on internal entanglement synchronization between cavity modes.
This paper is concerned with linear quantum networks of $N$ nondegenerate optical parametric amplifiers (NOPAs), with $N$ up to 6, which are interconnected in a coherent feedback chain. Each network connects two communicating parties (Alice and Bob) over two transmission channels. In previous work we have shown that a dual-NOPA coherent feedback network generates better Einstein-Podolsky-Rosen (EPR) entanglement (i.e., more two-mode squeezing) between its two outgoing Gaussian fields than a single NOPA, when the same total pump power is consumed and the systems undergo the same transmission losses over the same distance. This paper aims to analyze stability, EPR entanglement between two outgoing fields of interest, and bipartite entanglement of two-mode Gaussian states of cavity modes of the $N$-NOPA networks under the effect of transmission and amplification losses, as well as time delays. It is numerically shown that, in the absence of losses and delays, the network with more NOPAs in the chain requires less total pump power to generate the same degree of EPR entanglement. Moreover, we report on the internal entanglement synchronization that occurs in the steady state between certain pairs of Gaussian oscillator modes inside the NOPA cavities of the networks.