Multimode entanglement in reconfigurable graph states using optical frequency combs.

Multimode entanglement is an essential resource for quantum information processing and quantum metrology. However, multimode entangled states are generally constructed by targeting a specific graph configuration. This yields to a fixed experimental setup that therefore exhibits reduced versatility and scalability. Here we demonstrate an optical on-demand, reconfigurable multimode entangled state, using an intrinsically multimode quantum resource and a homodyne detection apparatus. Without altering either the initial squeezing source or experimental architecture, we realize the construction of thirteen cluster states of various sizes and connectivities as well as the implementation of a secret sharing protocol. In particular, this system enables the interrogation of quantum correlations and fluctuations for any multimode Gaussian state. This initiates an avenue for implementing on-demand quantum information processing by only adapting the measurement process and not the experimental layout.

Multipartite Entanglement of a Two-Separable State.

We consider a six-partite, continuous-variable quantum state that we have effectively generated by the parametric down-conversion of a femtosecond frequency comb. We show that, though this state is two-separable, i.e., it does not exhibit "genuine entanglement," it is undoubtedly multipartite entangled. The consideration of not only the entanglement of individual mode decompositions, but also of combinations of those, solves the puzzle and exemplifies the importance of studying different categories of multipartite entanglement.

Full multipartite entanglement of frequency-comb Gaussian states.

An analysis is conducted of the multipartite entanglement for Gaussian states generated by the parametric down-conversion of a femtosecond frequency comb. Using a recently introduced method for constructing optimal entanglement criteria, a family of tests is formulated for mode decompositions that extends beyond the traditional bipartition analyses. A numerical optimization over this family is performed to achieve maximal significance of entanglement verification. For experimentally prepared 4-, 6-, and 10-mode states, full entanglement is certified for all of the 14, 202, and 115 974 possible nontrivial partitions, respectively.

Time-resolved tryptophan fluorescence in flavodoxins.

The time-resolved fluorescence characteristics of tryptophan in flavodoxins isolated from the bacteriaDesulfovibrio gigas, Desulfovibrio vulgaris, Clostridium beijerinckii, andMegasphaera elsdenii were examined. The fluorescence decays were recorded using pulsed synchrotron radiation as the excitation source and time-correlated single-photon counting in detection. The results were analyzed as lifetime distributions using the maximum entropy method. Comparison of the fluorescence decays of normal and flavin mononucleotide-depleted flavodoxins demonstrates that radiationless energy transfer from tryptophan to flavin occurs in all flavodoxins investigated. On comparing the lifetime distribution patterns of apo and holoflavodoxins, it was noticed that a certain amount of apoprotein is present in all holoflavodoxin samples. The three-dimensional structure of two flavodoxins allowed us to compare experimental with theoretical transfer rates and the results were in fair agreement.

Motion of aromatic side chains, picosecond fluorescence, and internal energy transfer in Escherichia coli thioredoxin studied by site-directed mutagenesis, time-resolved fluorescence spectroscopy, and molecular dynamics simulations.

We have determined the picosecond fluorescence of the four aromatic amino acid residues (W28, W31, Y49, and Y70) in wild-type Escherichia coli thioredoxin (wt Trx) and a mutant Trx with W31 replaced by phenylalanine, Trx-W28-W31F. The internal motions of the four aromatic side chains were also analyzed. We examined the possibility of using internal energy transfer from tyrosine to tryptophan as a measure of long-range distances. The major features of the lifetime distribution of tryptophan fluorescence were unchanged in the W31F mutation, indicating that the environment of W28 is similar in both wt Trx and Trx-W28-W31F. However, the mutation of W31F changed the mobility of W28, situated close to the active-site disulfide/dithiol, but not the mobility of two tyrosines, Y49 and Y70, situated on the other side of the molecule. The mobility of the two tyrosine residues increased upon reduction of the active-site disulfide, indicating a looser structure with reduction. This increased motion could also be seen from molecular dynamics simulations. The change in energy transfer rates, as judged by tyrosine fluorescence lifetimes, was in agreement with energy transfer rates calculated from the molecular dynamics simulations. The anisotropy of tryptophan and tyrosine fluorescence could be separated in three parts: (I) overall rotation of the protein (10(-9)s), (II) internal mobility of side chains (10(-10)s), and (III) a very fast relaxation (10(-12)s). We can only experimentally detect this very fast relaxation when the internal motion is not present.

Side chain mobility in bovine calbindin D9k. Rotational motion of Tyr13.

The local motion of Tyr13 in wild type and mutant calbindin (Mr 8500, 75 amino acids) was investigated by time-resolved fluorescence spectroscopy performed at the MAX synchrotron in Lund, Sweden. Two-dimensional fluorescence spectroscopy (excitation-emission mapping) was used to characterize the emission of Tyr13 against the background of phenylalanine residues in the presence and absence of Ca2+. Local restricted motion of Tyr13 is observed in wild-type calbindin with only minor differences between the Ca2(+)-saturated and Ca2(+)-free forms. In a mutant, where Pro20 is exchanged for Gly and Ala14 and Asn21 are deleted, the local mobility of Tyr13 is enhanced close to values characteristic for free rotational diffusion. An increase of the overall rotational motion in this mutant form by a factor of two and the enhanced local mobility of Tyr13 indicate local and global conformational changes that also affect the Ca2(+)-binding properties. Tyr13 occurs in two isomeric species differing in lifetime of the excited state; the major species is populated to 85-90%.

Auto-traction for treatment of lumbago-sciatica. A multicentre controlled investigation.

In this controlled prospective study of the Auto-traction method for the treatment of lumbago-sciatica, 82 patients were randomly allocated to either treatment with Auto-traction for up to three 1-hour sessions in 1 week, or they were given a corset and advised to rest. The orthopaedic surgeons participating in the study worked at six different hospitals and all had limited experience of the Auto-traction method obtained during a 1-week course. All patients were clinically evaluated by an independent observer who also performed the follow-up examinations 1 and 3 weeks after the treatment sessions. In addition a 3-month follow-up was performed by letter. The Auto-traction method gave prompt relief of pain and a normalizing of the SLR test more often than treatment with only a corset and rest. The difference between the two treatment groups was statistically significant. The immediate difference noted between the treatment groups had decreased slightly at 3 weeks but was still statistically significant at this time.