8 research outputs found
Entanglement breaking channels and entanglement sudden death
The occurrence of entanglement sudden death in the evolution of a bipartite
system depends on both the initial state and the channel responsible for the
evolution. An extreme case is that of entanglement braking channels, which are
channels that acting on only one of the subsystems drives them to full
disentanglement regardless of the initial state. In general, one can find
certain combinations of initial states and channels acting on one or both
subsystems that can result in entanglement sudden death or not. Neither the
channel nor the initial state, but their combination, is responsible for this
effect, but their combination. In this work we show that, in all cases, when
entanglement sudden death occurs, the evolution can be mapped to that of an
effective entanglement breaking channel on a modified initial state. Our
results allow to anticipate which states will suffer entanglement sudden death
or not for a given evolution. An experiment with polarization entangled photons
demonstrates the utility of this result in a variety of cases
Resilience of hybrid optical angular momentum qubits to turbulence
Recent schemes to encode quantum information into the total angular momentum
of light, defining rotation-invariant hybrid qubits composed of the
polarization and orbital angular momentum degrees of freedom, present
interesting applications for quantum information technology. However, there
remains the question as to how detrimental effects such as random spatial
perturbations affect these encodings. Here, we demonstrate that alignment-free
quantum communication through a turbulent channel based on hybrid qubits can
be achieved with unit transmission fidelity. In our experiment, alignment-free
qubits are produced with q-plates and sent through a homemade turbulence
chamber. The decoding procedure, also realized with q-plates, relies on both
degrees of freedom and renders an intrinsic error-filtering mechanism that
maps errors into losses