Complementarity and Information in "Delayed-choice for entanglement swapping"

Building on Peres's idea of "Delayed-choice for extanglement swapping" we show that even the degree to which quantum systems were entangled can be defined after they have been registered and may even not exist any more. This does not arise as a paradox if the quantum state is viewed as just a representative of information. Moreover such a view gives a natural quantification of the complementarity between the measure of information about the input state for teleportation and the amount of entanglement of the resulting swapped entangled state.Comment: 5 pages, 2 figures, submitted to the special issue of Foundation of Physics in honor of Asher Peres' 70th birthda

Optical properties of the NGC 5328 group of galaxies

We present the results of a photometric and spectroscopic study of seven members of the NGC 5328 group of galaxies, a chain of galaxies spanning over 200 kpc (H_0 = 70 km/s/Mpc). We analyze the galaxy structure and study the emission line properties of the group members looking for signatures of star formation and AGN activity. We finally attempt to infer, from the modeling of line-strength indices, the stellar population ages of the early-type members. We investigate also the presence of a dwarf galaxy population associated with the bright members. The group is composed of a large fraction of early-type galaxies including NGC 5328 and NGC 5330, two bona fide ellipticals at the center of the group. In both galaxies no recent star formation episodes are detected by the H_beta vs. MgFe indices of these galaxies. 2MASX J13524838-2829584 has extremely boxy isophotes which are believed to be connected to a merging event: line strength indices suggest that this object probably had a recent star formation episode. A warped disc component emerges from the model subtracted image of 2MASX J13530016-2827061 which is interpreted as a signature of an ongoing interaction with the rest of the group. Ongoing star formation and nuclear activity is present in the projected outskirts of the group. The two early-type galaxies 2MASX J13523852-2830444 and 2MASX J13525393-2831421 show spectral signatures of star formation, while a Seyfert 2 type nuclear activity is detected in MCG -5-33-29.Comment: 18 pages, 12 figures, accepted for publication in MNRA

Comment on "Exclusion of time in the theorem of Bell" by K. Hess and W. Philipp

A recent Letter by Hess and Philipp claims that Bell's theorem neglects the possibility of time-like dependence in local hidden variables, hence is not conclusive. Moreover the authors claim that they have constructed, in an earlier paper, a local realistic model of the EPR correlations. However, they themselves have neglected the experimenter's freedom to choose settings, while on the other hand, Bell's theorem can be formulated to cope with time-like dependence. This in itself proves that their toy model cannot satisfy local realism, but we also indicate where their proof of its local realistic nature fails.Comment: Latex needs epl.cl

Quantum state transmission in a cavity array via two-photon exchange

The dynamical behavior of a coupled cavity array is investigated when each cavity contains a three-level atom. For the uniform and staggered intercavity hopping, the whole system Hamiltonian can be analytically diagonalized in the subspace of single-atom excitation. The quantum state transfer along the cavities is analyzed in detail for distinct regimes of parameters, and some interesting phenomena including binary transmission, selective localization of the excitation population are revealed. We demonstrate that the uniform coupling is more suitable for the quantum state transfer. It is shown that the initial state of polariton located in the first cavity is crucial to the transmission fidelity, and the local entanglement depresses the state transfer probability. Exploiting the metastable state, the distance of the quantum state transfer can be much longer than that of Jaynes-Cummings-Hubbard model. A higher transmission probability and longer distance can be achieved by employing a class of initial encodings and final decodings.Comment: 8 pages, 7 figures. to appear in Phys. Rev.

Experimental Demonstration of Decoherence-Free One-Way Information Transfer

We report the experimental demonstration of a one-way quantum protocol reliably operating in the presence of decoherence. Information is protected by designing an appropriate decoherence-free subspace for a cluster state resource. We demonstrate our scheme in an all-optical setup, encoding the information into the polarization states of four photons. A measurement-based one-way information-transfer protocol is performed with the photons exposed to severe symmetric phase-damping noise. Remarkable protection of information is accomplished, delivering nearly ideal outcomes.Comment: 5 pages, 3 figures, RevTeX

A Bell-type test of energy-time entangled qutrits

We have performed a Bell-type test for energy-time entangled qutrits. A method of inferring the Bell violation in terms of an associated interference visibility is derived. Using this scheme we obtained a Bell value of $2.784 \pm 0.023$, representing a violation of $34 \sigma$ above the limit for local variables. The scheme has been developed for use at telecom wavelengths and using proven long distance quantum communication architecture to optimize the utility of this high dimensional entanglement resource.Comment: replaced lost acknowledement

A Novel Protocol-Authentication Algorithm Ruling Out a Man-in-the-Middle Attack in Quantum Cryptography

In this work we review the security vulnerability of Quantum Cryptography with respect to "man-in-the-middle attacks" and the standard authentication methods applied to counteract these attacks. We further propose a modified authentication algorithm which features higher efficiency with respect to consumption of mutual secret bits.Comment: 4 pages, submitted to the International Journal of Quantum Information, Proceedings of the meeting "Foundations of Quantum Information", Camerino, April 200