4,987 research outputs found
Impact of strong magnetic fields on collision mechanism for transport of charged particles
One of the main applications in plasma physics concerns the energy production
through thermo-nuclear fusion. The controlled fusion is achieved by magnetic
confinement i.e., the plasma is confined into a toroidal domain (tokamak) under
the action of huge magnetic fields. Several models exist for describing the
evolution of strongly magnetized plasmas, most of them by neglecting the
collisions between particles. The subject matter of this paper is to
investigate the effect of large magnetic fields with respect to a collision
mechanism. We consider here linear collision Boltzmann operators and derive, by
averaging with respect to the fast cyclotronic motion due to strong magnetic
forces, their effective collision kernels
Cooling a quantum circuit via coupling to a multiqubit system
The cooling effects of a quantum LC circuit coupled inductively with an
ensemble of artificial qubits are investigated. The particles may decay
independently or collectively through their interaction with the environmental
vacuum electromagnetic field reservoir. For appropriate bath temperatures and
the resonator's quality factors, we demonstrate an effective cooling well below
the thermal background. In particular, we found that for larger samples the
cooling efficiency is better for independent qubits. However, the cooling
process can be faster for collectively interacting particles.Comment: 5 pages, 3 figure
Optimal Light Beams and Mirror Shapes for Future LIGO Interferometers
We report the results of a recent search for the lowest value of thermal
noise that can be achieved in LIGO by changing the shape of mirrors, while
fixing the mirror radius and maintaining a low diffractional loss. The result
of this minimization is a beam with thermal noise a factor of 2.32 (in power)
lower than previously considered Mesa Beams and a factor of 5.45 (in power)
lower than the Gaussian beams employed in the current baseline design. Mirrors
that confine these beams have been found to be roughly conical in shape, with
an average slope approximately equal to the mirror radius divided by arm
length, and with mild corrections varying at the Fresnel scale. Such a mirror
system, if built, would impact the sensitivity of LIGO, increasing the event
rate of observing gravitational waves in the frequency range of maximum
sensitivity roughly by a factor of three compared to an Advanced LIGO using
Mesa beams (assuming all other noises remain unchanged). We discuss the
resulting beam and mirror properties and study requirements on mirror tilt,
displacement and figure error, in order for this beam to be used in LIGO
detectors.Comment: 9 pages, 11 figure
Loading atom lasers by collectivity-enhanced optical pumping
The effect of collectivity on the loading of an atom laser via optical
pumping is discussed. In our model, atoms in a beam are laser-excited and
subsequently spontaneously decay into a trapping state. We consider the case of
sufficiently high particle density in the beam such that the spontaneous
emission is modified by the particle interaction. We show that the collective
effects lead to a better population of the trapping state over a wide range of
system parameters, and that the second order correlation function of the atoms
can be controlled by the applied laser field.Comment: 5 pages, 7 figure
Quantum tunneling through vacuum-multiparticle induced potentials
The vacuum cavity mode induces a potential barrier and a well when an
ultra-slow excited atom enters the interaction region so that it can be
reflected or transmitted with a certain probability. We demonstrate here that a
slow-velocity excited particle tunnels freely through a vacuum electromagnetic
field mode filled with ground state atoms. The reason for this is the
trapping of the moving atom into its upper state due to multiparticle
influences and the corresponding decoupling from the interaction with the
environment such that the emitter does not {\it see} the induced potentials.Comment: Multiparticle samples, quantum tunneling, vacuum induced potential
Fast, Efficient Calculations of the Two-Body Matrix Elements of the Transition Operators for Neutrinoless Double Beta Decay
To extract information about the neutrino properties from the study of
neutrinoless double-beta (0\nu\beta\beta) decay one needs a precise computation
of the nuclear matrix elements (NMEs) associated with this process. Approaches
based on the Shell Model (ShM) are among the nuclear structure methods used for
their computation. ShM better incorporates the nucleon correlations, but have
to face the problem of the large model spaces and computational resources. The
goal is to develop a new, fast algorithm and the associated computing code for
efficient calculation of the two-body matrix elements (TBMEs) of the
0\nu\beta{\beta} decay transition operator, which are necessary to calculate
the NMEs. This would allow us to extend the ShM calculations for double-beta
decays to larger model spaces, of about 9-10 major harmonic oscillator shells.
The improvement of our code consists in a faster calculation of the radial
matrix elements. Their computation normally requires the numerical evaluation
of two-dimensional integrals: one over the coordinate space and the other over
the momentum space. By rearranging the expressions of the radial matrix
elements, the integration over the coordinate space can be performed
analytically, thus the computation reduces to sum up a small number of
integrals over momentum. Our results for the NMEs are in a good agreement with
similar results from literature, while we find a significant reduction of the
computation time for TBMEs, by a factor of about 30, as compared with our
previous code that uses two-dimensional integrals.Comment: 6 pages, one figur
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