We consider single photons propagating along two paths, with the polarization correlated to the path. Two
information related aspects of this translational-internal entanglement (TIE) are analyzed: a) Using the polarization
to record the path (a "flying detector" scheme), we characterize the tradeoff between path- and phaseinformation.
b) We investigate the effects of non-Markovian noise on the two-qubit quantum channel consisting
of the photon path and polarization (that are both used to encode information), and suggest noise protection
Using quantum channels to transmit classical information has been proven to be advantageous in several scenarios.
These channels have been assumed to be memoryless, meaning that consecutive transmissions of information
are uncorrelated. However, as shown experimentally, such correlations do exist, and thereby retain memory
of previous information. This memory complicates the protection of entangled-information transmission from
We have recently addressed these fundamental questions by developing a generalized master equation for multipartite
entangled systems coupled to finite-temperature baths and subject to <i>arbitrary</i> external perturbations
whose role is to provide <i>dynamical protection</i> from decay and decoherence.
Here we explore and extend the foregoing strategy to quantum optical communication schemes wherein
polarization-entangled photons traverse a bit-flip channel with temporal and spatial memory, such that the
two channels experience cross-decoherence. We introduce a novel approach to the protection of the entangled
information from decoherence in such schemes. It is based on selectively modulating the photon polarizations in
We show that by applying selective modulation, one can independently control the symmetry and spatial
memory attributes of the channel. We then explore the effects of these attributes on the channel capacity.
Remarkably, we show that there is a nontrivial interplay between the effects of asymmetry and memory on the
A unified theory is given of dynamically modified decay and decoherence of field-driven multilevel multipartite entangled states that are weakly coupled to zero-temperature baths. The theory allows for arbitrary local differences in their coupling to the environment. Due to such differences, the optimal driving-field modulation to ensure maximal fidelity is found to substantially differ from conventional π-phase flips of the single-qubit evolution.