6,456 research outputs found
Exploiting quantum parallelism to simulate quantum random many-body systems
We present an algorithm that exploits quantum parallelism to simulate randomness in a quantum system. In our scheme, all possible realizations of the random parameters are encoded quantum mechanically in a superposition state of an auxiliary system. We show how our algorithm allows for the efficient simulation of dynamics of quantum random spin chains with known numerical methods. We propose an experimental realization based on atoms in optical lattices in which disorder could be simulated in parallel and in a controlled way through the interaction with another atomic species
Electromagnetic radiation initiated by hadronic jets from microquasars in the ISM
Microquasars are potential candidates to produce a non-negligible fraction of
the observed galactic cosmic rays. The protons accelerated at the jet
termination shock interact with the interstellar medium and may produce
detectable fluxes of extended emission at different energy bands: high-energy
and very high-energy gamma-rays produced by neutral pion-decay, synchrotron and
bremsstrahlung emission in a wide energy range generated by the secondary
electrons produced by charged pion-decay. We discuss the association between
this scenario and some of the unidentified EGRET sources in the galactic plane.Comment: (1)Universitat de Barcelona (2)Max Planck institute fur kernphysik,
11 pages, 14 figures, accepted for publication in Astronomy & Astrophysic
Phase diagram of Landau-Zener phenomena in coupled one-dimensional Bose quantum fluids
We study stationary and dynamical properties of the many-body Landau-Zener
dynamics of a Bose quantum fluid confined in two coupled one-dimensional
chains, using a many-body generalization recently reported [Y.-A. Chen et al.],
within the decoupling approximation and the one-level band scheme. The energy
spectrum evidences the structure of the avoided level crossings as a function
of the on-site inter particle interaction strength. On the dynamical side, a
phase diagram of the transfer efficiency across ground-state and inverse sweeps
is presented. A totally different scenario with respect to the original
single-particle Landau-Zener scheme is found for ground-state sweeps, in which
a breakdown of the adiabatic region emerges as the sweep rate decreases. On the
contrary, the transfer efficiency across inverse sweeps reveals consistent
results with the single-particle Landau-Zener predictions. In the strong
coupling regime, we find that there is a critical value of the on-site
interaction for which the transfer of particles starts to vanish independently
of the sweep rate. Our results are in qualitative agreement with those of the
experimental counterpart.Comment: 15 pages, submitted to Phys. Rev. A (new version
Constraining supersymmetry from the satellite experiments
In this paper we study the detectability of -rays from dark matter
annihilation in the subhalos of the Milky Way by the satellite-based
experiments, EGRET and GLAST. We work in the frame of supersymmetric extension
of the standard model and assume the lightest neutralino being the dark matter
particles. Based on the N-body simulation of the evolution of dark matter
subhalos we first calculate the average intensity distribution of this new
class of -ray sources by neutralino annihilation. It is possible to
detect these -ray sources by EGRET and GLAST. Conversely, if these
sources are not detected the nature of the dark matter particls will be
constrained by these experiments, which, however, depending on the
uncertainties of the subhalo profile.Comment: 19 pages, 5 gigures; references added, more discussions adde
Nonthermal processes and neutrino emission from the black hole GRO J0422+32 in a bursting state
GRO J0422+32 is a member of the class of low-mass X-ray binaries (LMXBs). It
was discovered during an outburst in 1992. During the entire episode a
persistent power-law spectral component extending up to MeV was
observed, which suggests that nonthermal processes should have occurred in the
system. We study relativistic particle interactions and the neutrino production
in the corona of GRO J0422+32, and explain the behavior of GRO J0422+32 during
its recorded flaring phase. We have developed a magnetized corona model to fit
the spectrum of GRO J0422+32 during the low-hard state. We also estimate
neutrino emission and study the detectability of neutrinos with 1 km
detectors, such as IceCube. The short duration of the flares ( hours) and
an energy cutoff around a few TeV in the neutrino spectrum make neutrino
detection difficult. There are, however, many factors that can enhance neutrino
emission. The northern-sky coverage and full duty cycle of IceCube make it
possible to detect neutrino bursts from objects of this kind through
time-dependent analysis.Comment: 12 pages, 11 figures, accepted for publication in A&
Direct equivalence between quantum phase transition phenomena in radiation-matter and magnetic systems: scaling of entanglement
We show that the quantum phase transition arising in a standard
radiation-matter model (Dicke model) belongs to the same universality class as
the infinitely-coordinated, transverse field XY model. The effective
qubit-qubit exchange interaction is shown to be proportional to the square of
the qubit-radiation coupling. A universal finite-size scaling is derived for
the corresponding two-qubit entanglement (concurrence) and a size-consistent
effective Hamiltonian is proposed for the qubit subsystem.Comment: 4 pages, 3 figures. Minor changes. Published versio
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