4,524 research outputs found
HI observations of dwarf galaxies out to a distance of 50 Mpc
Here we report our preliminary findings from an HI search for dwarf galaxies in three environmentally distinct regions of the sky: a galactic void, a galactic cluster, and an interaction field. This study is sensitive at the 5(sigma) level to hydrogen masses as low as 5 x 10(exp 5) solar mass. We have made three possible detections of previously uncatalogued objects: one in the void field, and two in the cluster field. Reduction of the interaction field is in progress
Encoding a qubit in an oscillator
Quantum error-correcting codes are constructed that embed a
finite-dimensional code space in the infinite-dimensional Hilbert space of a
system described by continuous quantum variables. These codes exploit the
noncommutative geometry of phase space to protect against errors that shift the
values of the canonical variables q and p. In the setting of quantum optics,
fault-tolerant universal quantum computation can be executed on the protected
code subspace using linear optical operations, squeezing, homodyne detection,
and photon counting; however, nonlinear mode coupling is required for the
preparation of the encoded states. Finite-dimensional versions of these codes
can be constructed that protect encoded quantum information against shifts in
the amplitude or phase of a d-state system. Continuous-variable codes can be
invoked to establish lower bounds on the quantum capacity of Gaussian quantum
channels.Comment: 22 pages, 8 figures, REVTeX, title change (qudit -> qubit) requested
by Phys. Rev. A, minor correction
Monopolies—Interstate Commerce—Organized Baseball
Toolson v. New York Yankees, Inc. et al ., 101 F. Supp. 93 (S. D. Cal. 1951)
Income Tax—Costs in Violation of Ceiling Prices Held Deductible
Commissioner v. Weisman, 197 F. 2d 221 (1st Cir. 1952); Hofferbert v. Anderson Oldsmobile, Inc., 197 F. 2d 504 (4th Cir. 1952); Commissioner v. Guminski, 198 F. 2d 265 (5th Cir. 1952)
On the Mass of M31
Recent work by several groups has established the properties of the dwarf
satellites to M31. We reexamine the reported kinematics of this group employing
a fresh technique we have developed previously. By calculating the distribution
of a chi statistic (which we define in the paper) for the M31 system, we
conclude that the total mass (disk plus halo) of the primary is unlikely to be
as great as that of our own Milky Way. In fact the chi distribution for M31
indicates that, like NGC 3992, it does not have a massive halo. In contrast,
the analysis of the satellites of NGC 1961 and NGC 5084 provides strong
evidence for massive halos surrounding both spiral galaxies.Comment: To appear in MNRAS, 10 pages with 6 figure
Quantum Communication and Computing With Atomic Ensembles Using Light-Shift Imbalance Induced Blockade
Recently, we have shown that for conditions under which the so-called
light-shift imbalance induced blockade (LSIIB) occurs, the collective
excitation of an ensemble of a multi-level atom can be treated as a closed two
level system. In this paper, we describe how such a system can be used as a
quantum bit (qubit) for quantum communication and quantum computing.
Specifically, we show how to realize a C-NOT gate using the collective qubit
and an easily accessible ring cavity, via an extension of the so-called
Pellizzari scheme. We also describe how multiple, small-scale quantum computers
realized using these qubits can be linked effectively for implementing a
quantum internet. We describe the details of the energy levels and transitions
in 87Rb atom that could be used for implementing these schemes.Comment: 16 pages, 9 figures. Accepted in Phys. Rev.
Generation and manipulation of squeezed states of light in optical networks for quantum communication and computation
We analyze a fiber-optic component which could find multiple uses in novel
information-processing systems utilizing squeezed states of light. Our approach
is based on the phenomenon of photon-number squeezing of soliton noise after
the soliton has propagated through a nonlinear optical fiber. Applications of
this component in optical networks for quantum computation and quantum
cryptography are discussed.Comment: 12 pages, 2 figures; submitted to Journal of Optics
Generation of Kerr non-Gaussian motional states of trapped ions
Non-Gaussian states represent a powerful resource for quantum information
protocols in the continuous variables regime. Cat states, in particular, have
been produced in the motional degree of freedom of trapped ions by controlled
displacements dependent on the ionic internal state. An alternative method
harnesses the Kerr nonlinearity naturally existent in this kind of system. We
present detailed calculations confirming its feasibility for typical
experimental conditions. Additionally, this method permits the generation of
complex non-Gaussian states with negative Wigner functions. Especially,
superpositions of many coherent states are achieved at a fraction of the time
necessary to produce the cat state.Comment: 6 pages, 5 figure
The extent of NGC 6822 revealed by its C stars population
Using the CFH12K camera, we apply the four band photometric technique to
identify 904 carbon stars in an area 28' x 42' centered on NGC 6822. A few C
stars, outside of this area were also discovered with the Las Campanas Swope
Telescope. The NGC 6822 C star population has an average I of 19.26 mag leading
to an average absolute I magnitude of
-4.70 mag, a value essentially identical to the mean magnitude obtained for
the C stars in IC 1613. Contrary to stars highlighting the optical image of NGC
6822, C stars are seen at large radial distances and trace a huge slightly
elliptical halo which do not coincide with the huge HI cloud surrounding
NGC6822. The previously unknown stellar component of NGC 6822 has a exponential
scale length of 3.0' +/- 0.1' and can be traced to five scale lengths. The C/M
ratio of NGC 6822 is evaluated to br 1.0 +/- 0.2.Comment: accepted, to be published in A
Photon-Number-Splitting versus Cloning Attacks in Practical Implementations of the Bennett-Brassard 1984 protocol for Quantum Cryptography
In practical quantum cryptography, the source sometimes produces multi-photon
pulses, thus enabling the eavesdropper Eve to perform the powerful
photon-number-splitting (PNS) attack. Recently, it was shown by Curty and
Lutkenhaus [Phys. Rev. A 69, 042321 (2004)] that the PNS attack is not always
the optimal attack when two photons are present: if errors are present in the
correlations Alice-Bob and if Eve cannot modify Bob's detection efficiency, Eve
gains a larger amount of information using another attack based on a 2->3
cloning machine. In this work, we extend this analysis to all distances
Alice-Bob. We identify a new incoherent 2->3 cloning attack which performs
better than those described before. Using it, we confirm that, in the presence
of errors, Eve's better strategy uses 2->3 cloning attacks instead of the PNS.
However, this improvement is very small for the implementations of the
Bennett-Brassard 1984 (BB84) protocol. Thus, the existence of these new attacks
is conceptually interesting but basically does not change the value of the
security parameters of BB84. The main results are valid both for Poissonian and
sub-Poissonian sources.Comment: 11 pages, 5 figures; "intuitive" formula (31) adde
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