21 research outputs found
Complementarity and correlations
We provide an interpretation of entanglement based on classical correlations
between measurement outcomes of complementary properties: states that have
correlations beyond a certain threshold are entangled. The reverse is not true,
however. We also show that, surprisingly, all separable nonclassical states
exhibit smaller correlations for complementary observables than some strictly
classical states. We use mutual information as a measure of classical
correlations, but we conjecture that the first result holds also for other
measures (e.g. the Pearson correlation coefficient or the sum of conditional
probabilities).Comment: Published version (+1 reference
A review on super dense coding over covariant noisy channels
We study the performance of the super dense coding protocol in the presence
of quantum channels with covariant noise. We first consider the bipartite case
and review in a unified way the case of general Pauli channels. We discuss both
the cases of unitary and non-unitary encoding. We also study the multipartite
scenario and investigate the case of many senders and one receiver.Comment: 11 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1107.359
Optimal super dense coding over noisy quantum channels
We investigate super dense coding in the presence of noise, i.e. the
subsystems of the entangled resource state have to pass a noisy unital quantum
channel between the sender and the receiver. We discuss explicitly the case of
Pauli channels in arbitrary dimension and derive the super dense coding
capacity (i.e. the optimal information transfer) for some given resource
states. We also study the case that the initial resource state can be chosen:
for the qubit depolarizing channel we show that there is a threshold value for
the noise parameter, below which the super dense coding protocol is optimized
by a maximally entangled initial state, while above the threshold the dense
coding capacity for any entangled initial state is smaller than the one for a
product state. Finally, we provide an example of a noisy channel where
non-unitary pre-processing increases the super dense coding capacity, as
compared to only unitary encoding.Comment: 22 pages, 5 figure