Enhancing entanglement of the two-mode squeezed vacuum state by arbitrary combinations of photon additions and subtractions
Yang Yang · Journal of the Optical Society of America B · 2019
We investigate the problem of enhancing quantum entanglement of the two-mode squeezed vacuum state by asymmetric combinations of photon additions and subtractions. Suppose a combination of N operations is performed on the two-mode squeezed vacuum state, in which each operation may be either photon addition or photon subtraction and may be performed on either mode A or mode B of the state; then there are (N+1)2N possible combinations in all. We calculate in detail the entanglement enhancement by all possible combinations for each given N∈{1,2,…,5,6}, respectively, and find that when the squeezing parameter is small, combinations such as aa†aa†…, a†aa†a…, and their equivalent ones always achieve the greatest enhancement of entanglement, while combinations such as aaaa…, a†a†a†a†…, and their equivalent ones always achieve the lowest enhancement of entanglement; when the squeezing parameter is great enough, entanglement enhancement by each combination is nearly the same. We also compare the maximal and minimal entanglement achieved by such combinations for N=1 to 6, and find that when the squeezing parameter is small, a combination of more operations may generate even less entanglement than a combination of fewer operations.