This is a reply to the comment from E. Amselem et al. on our paper (Phys. Rev. Lett. 109, 150401 (2012), arXiv:1207.0059).
We report an experiment that uses the environmental selection, a key concept in the recent theory of quantum Darwinism, as a mechanism to realize the entanglement filter, a useful quantum information device that filters out certain entangled states.
In the experiment, the environment of two qubits is controlled to favor an entangled state and kill other competing components in the input state. The initial state has vanishing entanglement, but the state surviving after interaction with the environment is close to a maximally entangled state, with an entanglement fidelity of $(94.7pm 1.9)%$ measured through the quantum state tomography. We experimentally demonstrate that the generated entanglement is robust under change of the initial state configurations and the environmental parameters.
We report an experiment that demonstrates full function of a quantum router using entangled photons, where the paths of a single-photon pulse are controlled in a coherent fashion by polarization of another single photon. Through a projective measurem
ent, we prepare the polarization of the control photon in arbitrary superposition states, leading to coherent routing of the target photon in quantum superposition of different paths. We demonstrate quantum nature of this router through optical measurements based on quantum state tomography and show an average fidelity of $(93.24pm 0.23)%$ for the quantum routing operation.
We report the first state-independent experimental test of quantum contextuality on a single photonic qutrit (three-dimensional system), based on a recent theoretical proposal [Yu and Oh, Phys. Rev. Lett. 108, 030402 (2012)]. Our experiment spotlight
s quantum contextuality in its most basic form, in a way that is independent of either the state or the tensor product structure of the system.
