Entropy gain and the Choi–Jamiolkowski correspondence for infinite-dimensional quantum evolutions

We consider the entropy gain for infinite-dimensional evolutions and show that unlike in the finite-dimensional case, there are many channels with positive minimal entropy gain. We obtain a new lower bound and compute the minimal entropy gain for a broad class of bosonic Gaussian channels. We mathematically formulate the Choi–Jamiolkowski (CJ) correspondence between channels and states in the infinite-dimensional case in a form close to the form used in quantum information theory. In particular, we obtain an explicit expression for the CJ operator defining a general nondegenerate bosonic Gaussian channel and compute its norm.