Abstract

When we combine quantum channel simulation with quantum teleportation, we obtain remarkable results regarding the natural limitations that quantum mechanics imposes on the optimal performance of any quantum task performed over quantum channels. Usually these ultimate limits are very difficult to address since the strategies employed to assess them are very general and involve adaptive, i.e. feedback-assisted, quantum operations, where feedback from the output is used to update the input. In this scenario, we first show that port-based teleportation for channel simulation can be exploited to devise a reduction procedure (dubbed stretching), by means of which the output of an adaptive protocol over arbitrary quantum channels is decomposed in terms of the tensor product of multicopies of the channel’s Choi state. When we specify this technique for quantum channel discrimination, we are able to derive a universal computable lower bound on the probability of the error affecting the discrimination between two arbitrary finite-dimensional quantum channels. We then show that our methodology can be applied also to quantum metrology, where we characterize the Heisenberg scaling as a direct consequence of port-based teleportation. In the second part of this talk we present a different design of quantum channel simulation that relies on a suitable control system and allows to simulate average quantum channels which are expressed in terms of ensemble of channels, even when these channel-components cannot be simulated through teleportation. We then derive relative-entropy-of-entanglement upper bounds for private communication over various channels as the amplitude damping channel, non-Gaussian mixtures of bosonic lossy channels and the dephrasure channel.