Efficient low-threshold lasers based on an erbium-doped holey fiber

We report experimental results on the continuous-wave lasers based on a small core erbium-doped holey fiber. In a simple Fabry-Perot-type cavity with high output coupling, we demonstrate low-threshold (0.55 mW) high slope-efficiency (57.3%) operation confirming both the quality and exceptionally high gain efficiency of the fiber. In an all-fiber ring cavity where the cavity loss is reduced, we show that it is possible to achieve a low-threshold laser with extremely wide tunability (>100 nm around 1550 nm). Our results illustrate some of the unique opportunities provided by active small core holey fibers

Nucleotide specificity of the enzymatic and motile activities of dynein, kinesin, and heavy meromyosin.

The substrate specificities of dynein, kinesin, and myosin substrate turnover activity and cytoskeletal filament-driven translocation were examined using 15 ATP analogues. The dyneins were more selective in their substrate utilization than bovine brain kinesin or muscle heavy meromyosin, and even different types of dyneins, such as 14S and 22S dynein from Tetrahymena cilia and the beta-heavy chain-containing particle from the outer-arm dynein of sea urchin flagella, could be distinguished by their substrate specificities. Although bovine brain kinesin and muscle heavy meromyosin both exhibited broad substrate specificities, kinesin-induced microtubule translocation varied over a 50-fold range in speed among the various substrates, whereas heavy meromyosin-induced actin translocation varied only by fourfold. With both kinesin and heavy meromyosin, the relative velocities of filament translocation did not correlate well with the relative filament-activated substrate turnover rates. Furthermore, some ATP analogues that did not support the filament translocation exhibited filament-activated substrate turnover rates. Filament-activated substrate turnover and power production, therefore, appear to become uncoupled with certain substrates. In conclusion, the substrate specificities and coupling to motility are distinct for different types of molecular motor proteins. Such nucleotide "fingerprints" of enzymatic activities of motor proteins may prove useful as a tool for identifying what type of motor is involved in powering a motility-related event that can be reconstituted in vitro

1 um Excess Sources in the UKIDSS - I. Three T Dwarfs in the SDSS Southern Equatorial Stripe

We report the discovery of two field brown dwarfs, ULAS J0128-0041 and ULAS J0321+0051, and the rediscovery of ULAS J0226+0051 (IfA 0230-Z1), in the Sloan Digital Sky Survey (SDSS) southern equatorial stripe. They are found in the course of our follow-up observation program of 1 um excess sources in the United Kingdom Infrared Telescope Infrared Deep Sky Survey. The Gemini Multi-Object Spectrographs spectra at red optical wavelengths (6500-10500 A) are presented, which reveal that they are early-T dwarfs. The classification is also supported by their optical to near-infrared colors. It is noted that ULAS J0321+0051 is one of the faintest currently known T dwarfs. The estimated distances to the three objects are 50-110 pc, thus they are among the most distant field T dwarfs known. Dense temporal coverage of the target fields achieved by the SDSS-II Supernova Survey allows us to perform a simple time-series analysis, which leads to the finding of significant proper motions of 150-290 mas/yr or the transverse velocities of 40-100 km/s for ULAS J0128-0041 and ULAS J0226+0051. We also find that there are no detectable, long-term (a-few-year) brightness variations above a few times 0.1 mag for the two brown dwarfs.Comment: Accepted for publication in the Astronomical Journal; Typos correcte

The Quantum State of an Ideal Propagating Laser Field

We give a quantum information-theoretic description of an ideal propagating CW laser field and reinterpret typical quantum-optical experiments in light of this. In particular we show that contrary to recent claims [T. Rudolph and B. C. Sanders, Phys. Rev. Lett. 87, 077903 (2001)], a conventional laser can be used for quantum teleportation with continuous variables and for generating continuous-variable entanglement. Optical coherence is not required, but phase coherence is. We also show that coherent states play a priveleged role in the description of laser light.Comment: 4 pages RevTeX, to appear in PRL. For an extended version see quant-ph/011115

Tailoring teleportation to the quantum alphabet

We introduce a refinement of the standard continuous variable teleportation measurement and displacement strategies. This refinement makes use of prior knowledge about the target state and the partial information carried by the classical channel when entanglement is non-maximal. This gives an improvement in the output quality of the protocol. The strategies we introduce could be used in current continuous variable teleportation experiments.Comment: 16 pages, 6 figures, RevTeX, made changes as recommended by referee, other minor textual corrections, resubmitted to Phys. Rev.

qBitcoin: A Peer-to-Peer Quantum Cash System

A decentralized online quantum cash system, called qBitcoin, is given. We design the system which has great benefits of quantization in the following sense. Firstly, quantum teleportation technology is used for coin transaction, which prevents from the owner of the coin keeping the original coin data even after sending the coin to another. This was a main problem in a classical circuit and a blockchain was introduced to solve this issue. In qBitcoin, the double-spending problem never happens and its security is guaranteed theoretically by virtue of quantum information theory. Making a block is time consuming and the system of qBitcoin is based on a quantum chain, instead of blocks. Therefore a payment can be completed much faster than Bitcoin. Moreover we employ quantum digital signature so that it naturally inherits properties of peer-to-peer (P2P) cash system as originally proposed in Bitcoin.Comment: 11 pages, 2 figure

The Mach-Zehnder and the Teleporter

We suggest a self-testing teleportation configuration for photon q-bits based on a Mach-Zehnder interferometer. That is, Bob can tell how well the input state has been teleported without knowing what that input state was. One could imagine building a "locked" teleporter based on this configuration. The analysis is performed for continuous variable teleportation but the arrangement could equally be applied to discrete manipulations.Comment: 4 pages, 5 figure