405 research outputs found
Readout scheme of the fullerene-based quantum computer by a single electron transistor
The readout of the quantum spin state is a challenge for any spin-based
quantum computing implementation. We propose a scheme, based on the achieved
technique of single electron transistor (SET), to implement the readout of
electronic spin state inside a doped fullerene by means of the
magnetic dipole-dipole coupling and spin filters. In the presence of an
external magnetic field, we show how to perform the spin state detection by
transforming the information contained in the spin state into the tunneling
current. The robustness of our scheme against sources of error is discussed.Comment: RevTex, 1 table and two figures. Latest versio
Central exclusive production of longlived gluinos at the LHC
We examine the possibility of producing gluino pairs at the LHC via the
exclusive reaction pp -> p+gluino+gluino+p in the case where the gluinos are
long lived. Such long lived gluinos are possible if the scalar super-partners
have large enough masses. We show that it may be possible to observe the
gluinos via their conversion to R-hadron jets and measure their mass to better
than 1% accuracy for masses below 350 GeV with 300/fb of data.Comment: 13 pages, 9 figures. Minor corrections to version
Disordered Hubbard Model with Attraction: Coupling Energy of Cooper Pairs in Small Clusters
We generalize the Cooper problem to the case of many interacting particles in
the vicinity of the Fermi level in the presence of disorder. On the basis of
this approach we study numerically the variation of the pair coupling energy in
small clusters as a function of disorder. We show that the Cooper pair energy
is strongly enhanced by disorder, which at the same time leads to the
localization of pairs.Comment: revtex, 5 pages, 6 figure
Effects of Neutrino Oscillation on the Supernova Neutrino Spectrum
The effects of three-flavor neutrino oscillation on the supernova neutrino
spectrum are studied. We calculate the expected event rate and energy spectra,
and their time evolution at the Superkamiokande (SK) and the Sudbury Neutrino
Observatory (SNO), by using a realistic neutrino burst model based on numerical
simulations of supernova explosions. We also employ a realistic density profile
based on a presupernova model for the calculation of neutrino conversion
probability in supernova envelopes. These realistic models and numerical
calculations allow us to quantitatively estimate the effects of neutrino
oscillation in a more realistic way than previous studies. We then found that
the degeneracy of the solutions of the solar neutrino problem can be broken by
the combination of the SK and SNO detections of a future Galactic supernova.Comment: 10 pages, 14 figures, corrected versio
Parity Violation in Proton-Proton Scattering
Measurements of parity-violating longitudinal analyzing powers (normalized
asymmetries) in polarized proton-proton scattering provide a unique window on
the interplay between the weak and strong interactions between and within
hadrons. Several new proton-proton parity violation experiments are presently
either being performed or are being prepared for execution in the near future:
at TRIUMF at 221 MeV and 450 MeV and at COSY (Kernforschungsanlage Juelich) at
230 MeV and near 1.3 GeV. These experiments are intended to provide stringent
constraints on the set of six effective weak meson-nucleon coupling constants,
which characterize the weak interaction between hadrons in the energy domain
where meson exchange models provide an appropriate description. The 221 MeV is
unique in that it selects a single transition amplitude (3P2-1D2) and
consequently constrains the weak meson-nucleon coupling constant h_rho{pp}. The
TRIUMF 221 MeV proton-proton parity violation experiment is described in some
detail. A preliminary result for the longitudinal analyzing power is Az = (1.1
+/-0.4 +/-0.4) x 10^-7. Further proton-proton parity violation experiments are
commented on. The anomaly at 6 GeV/c requires that a new multi-GeV
proton-proton parity violation experiment be performed.Comment: 13 Pages LaTeX, 5 PostScript figures, uses espcrc1.sty. Invited talk
at QULEN97, International Conference on Quark Lepton Nuclear Physics --
Nonperturbative QCD Hadron Physics & Electroweak Nuclear Processes --, Osaka,
Japan May 20--23, 199
Pulsed Magnetic Field Measurements of the Composite Fermion Effective Mass
Magnetotransport measurements of Composite Fermions (CF) are reported in 50 T
pulsed magnetic fields. The CF effective mass is found to increase
approximately linearly with the effective field , in agreement with our
earlier work at lower fields. For a of 14 T it reaches , over 20
times the band edge electron mass. Data from all fractions are unified by the
single parameter for all the samples studied over a wide range of
electron densities. The energy gap is found to increase like at
high fields.Comment: Has final table, will LaTeX without error
Optical Detection of a Single Nuclear Spin
We propose a method to optically detect the spin state of a 31-P nucleus
embedded in a 28-Si matrix. The nuclear-electron hyperfine splitting of the
31-P neutral-donor ground state can be resolved via a direct frequency
discrimination measurement of the 31-P bound exciton photoluminescence using
single photon detectors. The measurement time is expected to be shorter than
the lifetime of the nuclear spin at 4 K and 10 T.Comment: 4 pages, 3 figure
Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star
We investigate the initial progenitor mass dependence of the early-phase
neutrino signal from supernovae taking neutrino oscillations into account. The
early-phase analysis has advantages in that it is not affected by the time
evolution of the density structure of the star due to shock propagation or
whether the remnant is a neutron star or a black hole. The initial mass affects
the evolution of the massive star and its presupernova structure, which is
important for two reasons when considering the neutrino signal. First, the
density profile of the mantle affects the dynamics of neutrino oscillation in
supernova. Second, the final iron core structure determines the features of the
neutrino burst, i.e., the luminosity and the average energy. We find that both
effects are rather small. This is desirable when we try to extract information
on neutrino parameters from future supernova-neutrino observations. Although
the uncertainty due to the progenitor mass is not small for intermediate
(), we
can, nevertheless, determine the character of the mass hierarchy and whether
is very large or very small.Comment: 8 pages, 15 figure
Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation
The fully nonlinear response of a many-level tunneling system to a strong
alternating field of high frequency is studied in terms of the
Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent
tunneling current is calculated exactly and its resonance structure is
elucidated. In particular, it is shown that under certain reasonable conditions
on the physical parameters, the Fourier component is sharply peaked at
, where is the spacing between
two levels. This frequency multiplication results from the highly nonlinear
process of photon absorption (or emission) by the tunneling system. It is
also conjectured that this effect (which so far is studied mainly in the
context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from
[email protected], submitted to Phys.Rev.
A switchable controlled-NOT gate in a spin-chain NMR quantum computer
A method of switching a controlled-NOT gate in a solid-stae NMR quantum
computer is presented. Qubits of I=1/2 nuclear spins are placed periodically
along a quantum spin chain (1-D antiferromagnet) having a singlet ground state
with a finite spin gap to the lowest excited state caused by some quantum
effect. Irradiation of a microwave tuned to the spin gap energy excites a
packet of triplet magnons at a specific part of the chain where control and
target qubits are involved. The packet switches on the Suhl-Nakamura
interaction between the qubits, which serves as a controlled NOT gate. The
qubit initialization is achieved by a qubit initializer consisting of
semiconducting sheets attached to the spin chain, where spin polarizations
created by the optical pumping method in the semiconductors are transferred to
the spin chain. The scheme allows us to separate the initialization process
from the computation, so that one can optimize the computation part without
being restricted by the initialization scheme, which provides us with a wide
selection of materials for a quantum computer.Comment: 8 pages, 5 figure
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