1,623 research outputs found
Quantum mode filtering of non-Gaussian states for teleportation-based quantum information processing
We propose and demonstrate an effective mode-filtering technique of
non-Gaussian states generated by photon-subtraction. More robust non-Gaussian
states have been obtained by removing noisy low frequencies from the original
mode spectrum. We show that non-Gaussian states preserve their non-classicality
after quantum teleportation to a higher degree, when they have been
mode-filtered. This is indicated by a stronger negativity of
the Wigner function at the origin, compared to for states
that have not been mode-filtered. This technique can be straightforwardly
applied to various kinds of photon-subtraction protocols, and can be a key
ingredient in a variety of applications of non-Gaussian states, especially
teleportation-based protocols towards universal quantum information processing
Evolutionary origin of power-laws in Biochemical Reaction Network; embedding abundance distribution into topology
The evolutionary origin of universal statistics in biochemical reaction
network is studied, to explain the power-law distribution of reaction links and
the power-law distributions of chemical abundances. Using cell models with
catalytic reaction network, we find evidence that the power-law distribution in
abundances of chemicals emerges by the selection of cells with higher growth
speeds. Through the further evolution, this inhomogeneity in chemical
abundances is shown to be embedded in the distribution of links, leading to the
power-law distribution. These findings provide novel insights into the nature
of network evolution in living cells.Comment: 11 pages, 3 figure
Minimum cbits for remote preperation and measurement of a qubit
We show that a qubit chosen from equatorial or polar great circles on a Bloch
spehere can be remotely prepared with one cbit from Alice to Bob if they share
one ebit of entanglement. Also we show that any single particle measurement on
an arbitrary qubit can be remotely simulated with one ebit of shared
entanglement and communication of one cbit.Comment: Latex, 7 pages, minor changes, references adde
A New Constraint on the Ly Fraction of UV Very Bright Galaxies at Redshift 7
We study the extent to which very bright (-23.0 < MUV < -21.75) Lyman-break
selected galaxies at redshifts z~7 display detectable Lya emission. To explore
this issue, we have obtained follow-up optical spectroscopy of 9 z~7 galaxies
from a parent sample of 24 z~7 galaxy candidates selected from the 1.65 sq.deg
COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared
public survey data, and new ultra-deep Subaru z'-band imaging (which we also
present and describe in this paper). Our spectroscopy has yielded only one
possible detection of Lya at z=7.168 with a rest-frame equivalent width EW_0 =
3.7 (+1.7/-1.1) Angstrom. The relative weakness of this line, combined with our
failure to detect Lya emission from the other spectroscopic targets allows us
to place a new upper limit on the prevalence of strong Lya emission at these
redshifts. For conservative calculation and to facilitate comparison with
previous studies at lower redshifts, we derive a 1-sigma upper limit on the
fraction of UV bright galaxies at z~7 that display EW_0 > 50 Angstrom, which we
estimate to be < 0.23. This result may indicate a weak trend where the fraction
of strong Lya emitters ceases to rise, and possibly falls between z~6 and z~7.
Our results also leave open the possibility that strong Lya may still be more
prevalent in the brightest galaxies in the reionization era than their fainter
counterparts. A larger spectroscopic sample of galaxies is required to derive a
more reliable constraint on the neutral hydrogen fraction at z~7 based on the
Lya fraction in the bright galaxies.Comment: 20 pages, 7 figures, accepted for publication in Ap
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
Peres-Horodecki separability criterion for continuous variable systems
The Peres-Horodecki criterion of positivity under partial transpose is
studied in the context of separability of bipartite continuous variable states.
The partial transpose operation admits, in the continuous case, a geometric
interpretation as mirror reflection in phase space. This recognition leads to
uncertainty principles, stronger than the traditional ones, to be obeyed by all
separable states. For all bipartite Gaussian states, the Peres-Horodecki
criterion turns out to be necessary and sufficient condition for separability.Comment: 6 pages, no figure
New Improved Photometric Redshifts of Galaxies in the HDF
We report new improved photometric redshifts of 1048 galaxies in the Hubble
Deep Field (HDF). A standard chi^2 minimizing method is applied to seven-color
UBVIJHK photometry by Fernandez-Soto, Lanzetta, & Yahil (1999). We use 187
template SEDs representing a wide variety of morphology and age of observed
galaxies based on a population synthesis model by Kodama & Arimoto (1997). We
introduce two new recipes. First, the amount of the internal absorption is
changed as a free parameter in the range of E(B-V)=0.0 to 0.5 with an interval
of 0.1. Second, the absorption due to intergalactic HI clouds is also changed
by a factor of 0.5, 1.0, and 1.5 around the opacity given by Madau (1995). The
total number of template SEDs is thus 187x6x3=3,366, except for the redshift
grid. The dispersion sigma_z of our photometric redshifts with respect to
spectroscopic redshifts is sigma_z=0.08 and 0.24 for z2, respectively,
which are smaller than the corresponding values (sigma_z=0.09 and 0.45) by
Fernandez-Soto et al. Improvement is significant, especially in z>2. This is
due to smaller systematic errors which are largely reduced mainly by including
three opacities due to intergalactic HI clouds. We discuss redshift
distribution N(z) and cosmic star formation rate based on our new photometric
redshifts.Comment: 24 pages including 16 eps figures; accepted for publication in Ap
Generation and Eight-port Homodyne Characterization of Time-bin Qubits for Continuous-variable Quantum Information Processing
We experimentally generate arbitrary time-bin qubits using continuous-wave
light. The advantage unique to our qubit is its compatibility with
deterministic continuous-variable quantum information processing. This
compatibility comes from its optical coherence with continuous waves,
well-defined spatio-temporal mode, and frequency spectrum within the
operational bandwidth of the current continuous-variable technology. We also
demonstrate an efficient scheme to characterize time-bin qubits via eight-port
homodyne measurement. This enables the complete characterization of the qubits
as two-mode states, as well as a flexible analysis equivalent to the
conventional scheme based on a Mach-Zehnder interferometer and
photon-detection
On the distillation and purification of phase-diffused squeezed states
Recently it was discovered that non-Gaussian decoherence processes, such as
phase-diffusion, can be counteracted by purification and distillation protocols
that are solely built on Gaussian operations. Here, we make use of this
experimentally highly accessible regime, and provide a detailed experimental
and theoretical analysis of several strategies for purification/distillation
protocols on phase-diffused squeezed states. Our results provide valuable
information for the optimization of such protocols with respect to the choice
of the trigger quadrature, the trigger threshold value and the probability of
generating a distilled state
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