32,988 research outputs found
Simple scheme for two-qubit Grover search in cavity QED
Following the proposal by F. Yamaguchi et al.[Phys. Rev. A 66, 010302 (R)
(2002)], we present an alternative way to implement the two-qubit Grover search
algorithm in cavity QED. Compared with F. Yamaguchi et al.'s proposal, with a
strong resonant classical field added, our method is insensitive to both the
cavity decay and thermal field, and doesn't require that the cavity remain in
the vacuum state throughout the procedure. Moreover, the qubit definitions are
the same for both atoms, which makes the experiment easier. The strictly
numerical simulation shows that our proposal is good enough to demonstrate a
two-qubit Grover's search with high fidelity.Comment: manuscript 10 pages, 2 figures, to appear in Phys. Rev.
Nebular Spectra of SN 1998bw Revisited: Detailed Study by One and Two Dimensional Models
Refined one- and two-dimensional models for the nebular spectra of the
hyper-energetic Type Ic supernova (SN) 1998bw, associated with the gamma-ray
burst GRB980425, from 125 to 376 days after B-band maximum are presented. One
dimensional, spherically symmetric spectrum synthesis calculations show that
reproducing features in the observed spectra, i.e., the sharply peaked [OI]
6300\AA doublet and MgI] 4570\AA emission, and the broad [FeII] blend around
5200\AA, requires the existence of a high-density O-rich core expanding at low
velocities (\lsim 8,000 km s) and of Fe-rich material moving faster
than the O-rich material. Synthetic spectra at late phases from aspherical
(bipolar) explosion models are also computed with a two-dimensional spectrum
synthesis code. The above features are naturally explained by the aspherical
model if the explosion is viewed from a direction close to the axis of symmetry
(), since the aspherical model yields a high-density O-rich
region confined along the equatorial axis. By examining a large parameter space
(in energy and mass), our best model gives following physical quantities: the
kinetic energy ergs \gsim 8 - 12 and the
main-sequence mass of the progenitor star M_{\rm ms} \gsim 30 - 35 \Msun. The
temporal spectral evolution of SN 1998bw also indicates mixing among Fe-, O-,
and C-rich regions, and highly clumpy structure.Comment: 38 pages, 22 figures. ApJ, 640 (01 April 2006 issue), in pres
Period halving of Persistent Currents in Mesoscopic Mobius ladders
We investigate the period halving of persistent currents(PCs) of
non-interacting electrons in isolated mesoscopic M\"{o}bius ladders without
disorder, pierced by Aharonov-Bhom flux. The mechanisms of the period halving
effect depend on the parity of the number of electrons as well as on the
interchain hopping. Although the data of PCs in mesoscopic systems are
sample-specific, some simple rules are found in the canonical ensemble average,
such as all the odd harmonics of the PCs disappear, and the signals of even
harmonics are non-negative. {PACS number(s): 73.23.Ra, 73.23.-b, 68.65.-k}Comment: 6 Pages with 3 EPS figure
Superluminal propagation of an optical pulse in a Doppler broadened three-state, single channel active Raman gain medium
Using a single channel active Raman gain medium we show a ns
advance time for an optical pulse of s propagating
through a 10 cm medium, a lead time that is comparable to what was reported
previously. In addition, we have verified experimentally all the features
associated with this single channel Raman gain system. Our results show that
the reported gain-assisted superluminal propagation should not be attributed to
the interference between the two frequencies of the pump field.Comment: 4 pages, 3 figure
Heralded Entanglement between Atomic Ensembles: Preparation, Decoherence, and Scaling
Heralded entanglement between collective excitations in two atomic ensembles
is probabilistically generated, stored, and converted to single photon fields.
By way of the concurrence, quantitative characterizations are reported for the
scaling behavior of entanglement with excitation probability and for the
temporal dynamics of various correlations resulting in the decay of
entanglement. A lower bound of the concurrence for the collective atomic state
of 0.9\pm 0.3 is inferred. The decay of entanglement as a function of storage
time is also observed, and related to the local dynamics.Comment: 4 page
Generation of N-qubit W state with rf-SQUID qubits by adiabatic passage
A simple scheme is presented to generate n-qubit W state with
rf-superconducting quantum interference devices (rf-SQUIDs) in cavity QED
through adiabatic passage. Because of the achievable strong coupling for
rf-SQUID qubits embedded in cavity QED, we can get the desired state with high
success probability. Furthermore, the scheme is insensitive to position
inaccuracy of the rf-SQUIDs. The numerical simulation shows that, by using
present experimental techniques, we can achieve our scheme with very high
success probability, and the fidelity could be eventually unity with the help
of dissipation.Comment: to appear in Phys. Rev.
A massive star origin for an unusual helium-rich supernova in an elliptical galaxy
The unusual helium-rich (type Ib) supernova SN 2005E is distinguished from
any supernova hitherto observed by its faint and rapidly fading light curve,
prominent calcium lines in late-phase spectra and lack of any mark of recent
star formation near the supernova location. These properties are claimed to be
explained by a helium detonation in a thin surface layer of an accreting white
dwarf (Perets et al. 2010). Here we report on observations of SN 2005cz
appeared in an elliptical galaxy, whose observed properties resemble those of
SN 2005E in that it is helium-rich and unusually faint, fades rapidly, shows
much weaker oxygen emission lines than those of calcium in the well-evolved
spectrum. We argue that these properties are best explained by a core-collapse
supernova at the low-mass end () of the range of massive stars
that explode (Smartt 2009). Such a low mass progenitor had lost its
hydrogen-rich envelope through binary interaction, having very thin oxygen-rich
and silicon-rich layers above the collapsing core, thus ejecting a very small
amount of radioactive Ni and oxygen. Although the host galaxy NGC 4589
is an elliptical, some studies have revealed evidence of recent star-formation
activity (Zhang et al. 2008), consistent with the core-collapse scenario.Comment: Accepted by Nature (24 March 2010), 32 pages including Supplementary
Informatio
Jacobi-Predictor-Corrector Approach for the Fractional Ordinary Differential Equations
We present a novel numerical method, called {\tt Jacobi-predictor-corrector
approach}, for the numerical solution of fractional ordinary differential
equations based on the polynomial interpolation and the Gauss-Lobatto
quadrature w.r.t. the Jacobi-weight function
. This method has the computational cost
O(N) and the convergent order , where and are, respectively, the
total computational steps and the number of used interpolating points. The
detailed error analysis is performed, and the extensive numerical experiments
confirm the theoretical results and show the robustness of this method.Comment: 24 pages, 5 figure
Alternative scheme for two-qubit conditional phase gate by adiabatic passage under dissipation
We check a recent proposal [H. Goto and K. Ichimura Phys. Rev. A 70, 012305
(2004)] for controlled phase gate through adiabatic passage under the influence
of spontaneous emission and the cavity decay. We show a modification of above
proposal could be used to generate the necessary conditional phase gates in the
two-qubit Grover search. Conditioned on no photon leakage either from the
atomic excited state or from the cavity mode during the gating period, we
numerically analyze the success probability and the fidelity of the two-qubit
conditional phase gate by adiabatic passage. The comparison made between our
proposed gating scheme and a previous one shows that Goto and Ichimura's scheme
is an alternative and feasible way in the optical cavity regime for two-qubit
gates and could be generalised in principle to multi-qubit gates.Comment: to appear in J. Phys.
Spectrum Analysis of the Type Ib Supernova 1999dn: Probable Identifications of C II and H-alpha
Low resolution spectra of SN 1999dn at early times are presented and compared
with synthetic spectra generated with the parameterized supernova
synthetic-spectrum code SYNOW. We find that the spectra of SN 1999dn strongly
resemble those of SN 1997X and SN 1984L, and hence we classify it as a Type Ib
event. Line-identifications are established through spectrum synthesis. Strong
evidence of both H-alpha and C II 6580 is found. We infer that H-alpha appears
first, before the time of maximum brightness, and then is blended with and
finally overwhelmed by the C II line after maximum; this favors a thin
high-velocity hydrogen skin in this Type Ib supernova.Comment: 15 pages, 3 figures. Accepted for publication in Ap
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