26,925 research outputs found
Requirement for quantum computation
We identify "proper quantum computation" with computational processes that
cannot be efficiently simulated on a classical computer. For optical quantum
computation, we establish "no-go" theorems for classes of quantum optical
experiments that cannot yield proper quantum computation, and we identify
requirements for optical proper quantum computation that correspond to
violations of assumptions underpinning the no-go theorems.Comment: 11 pages, no figure
New Results from a Near-Infrared Search for Hidden Broad-Line Regions in Ultraluminous Infrared Galaxies
This paper reports the latest results from a near-infrared search for hidden
broad-line regions (BLRs: FWHM >~ 2,000 km/s) in ultraluminous infrared
galaxies (ULIGs). The new sample contains thirty-nine ULIGs from the 1-Jy
sample selected for their lack of BLRs at optical wavelengths. The results from
this new study are combined with those from our previous optical and
near-infrared surveys to derive the fraction of all ULIGs with optical or
near-infrared signs of genuine AGN activity (either a BLR or [Si VI] emission).
Comparisons of the dereddened emission-line luminosities of the optical or
obscured BLRs detected in the ULIGs of the 1-Jy sample with those of optical
quasars indicate that the obscured AGN/quasar in ULIGs is the main source of
energy in at least 15 -- 25% of all ULIGs in the 1-Jy sample. This fraction is
30 -- 50% among ULIGs with L_ir > 10^{12.3} L_sun. These results are compatible
with those from recent mid-infrared spectroscopic surveys carried out with ISO.
(abridged)Comment: 40 pages including 10 figures and 3 tables (Table 3 should be printed
in landscape mode
INTERNATIONAL TRADE POLICY: CHALLENGES AND OPPORTUNITIES FOR U.S. AGRICULTURE
International Relations/Trade,
Major Galaxy Mergers and the Growth of Supermassive Black Holes in Quasars
Despite observed strong correlations between central supermassive black holes
(SMBHs) and star-formation in galactic nuclei, uncertainties exist in our
understanding of their coupling. We present observations of the ratio of
heavily-obscured to unobscured quasars as a function of cosmic epoch up to z~3,
and show that a simple physical model describing mergers of massive, gas-rich
galaxies matches these observations. In the context of this model, every
obscured and unobscured quasar represent two distinct phases that result from a
massive galaxy merger event. Much of the mass growth of the SMBH occurs during
the heavily-obscured phase. These observations provide additional evidence for
a causal link between gas-rich galaxy mergers, accretion onto the nuclear SMBH
and coeval star formation.Comment: Accepted for publication in Science. Published by Science Express on
March 25th. 17 pages, 5 figures, including supplemental online materia
Quantum Encodings in Spin Systems and Harmonic Oscillators
We show that higher-dimensional versions of qubits, or qudits, can be encoded
into spin systems and into harmonic oscillators, yielding important advantages
for quantum computation. Whereas qubit-based quantum computation is adequate
for analyses of quantum vs classical computation, in practice qubits are often
realized in higher-dimensional systems by truncating all but two levels,
thereby reducing the size of the precious Hilbert space. We develop natural
qudit gates for universal quantum computation, and exploit the entire
accessible Hilbert space. Mathematically, we give representations of the
generalized Pauli group for qudits in coupled spin systems and harmonic
oscillators, and include analyses of the qubit and the infinite-dimensional
limits.Comment: 4 pages, published versio
STOL Simulation Requirements for Development of Integrated Flight/propulsion Control Systems
The role and use of simulation as a design tool in developing integrated systems where design criteria is largely unavailable is well known. This paper addresses additional simulation needs for the development of Integrated Flight/Propulsion Control Systems (IFPCS) which will improve the probability of properly interpreting simulation results. These needs are based on recent experience with power approach flying qualities evaluations of an advanced fighter configuration which incorporated Short Takeoff and Landing (STOL) technologies and earlier experiences with power approach flying qualities evaluations on the AFTI/F-16 program. The use of motion base platforms with axial and normal degrees of freedom will help in evaluating pilot coupling and workload in the presence of high frequency low amplitude axial accelerations produced by high bandwidth airspeed controllers in a gusty environment
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