4,949 research outputs found
Muon bundles from the Universe
Recently the CERN ALICE experiment, in its dedicated cosmic ray run, observed
muon bundles of very high multiplicities, thereby confirming similar findings
from the LEP era at CERN (in the CosmoLEP project). Significant evidence for
anisotropy of arrival directions of the observed high multiplicity muonic
bundles is found. Estimated directionality suggests their possible
extragalactic provenance. We argue that muonic bundles of highest multiplicity
are produced by strangelets, hypothetical stable lumps of strange quark matter
infiltrating our Universe.Comment: 4 pages, Proceedings for 17th International Conference on Strangeness
in Quark Matter, Utrecht, the Netherland
On the possibility of q-scaling in high energy production processes
It has been noticed recently that transverse momenta (p_T) distributions
observed in high energy production processes exhibit remarkably universal
scaling behaviour. This is the case when a suitable variable replaces the usual
p_T. On the other hand, it is also widely known that transverse momentum
distributions in general follow a power-like Tsallis distribution, rather than
an exponential Boltzmann-Gibbs, with a (generally energy dependent)
nonextensivity parameter q. Here we show that it is possible to choose a
suitable variable such that all the data can be fitted by the same Tsallis
distribution (with the same, energy independent value of the q-parameter). Thus
they exhibit q-scaling.Comment: Final version, accepted by J.Phys.
Polarization-controlled single photons
Vacuum-stimulated Raman transitions are driven between two magnetic substates
of a rubidium-87 atom strongly coupled to an optical cavity. A magnetic field
lifts the degeneracy of these states, and the atom is alternately exposed to
laser pulses of two different frequencies. This produces a stream of single
photons with alternating circular polarization in a predetermined
spatio-temporal mode. MHz repetition rates are possible as no recycling of the
atom between photon generations is required. Photon indistinguishability is
tested by time-resolved two-photon interference.Comment: 4 pages, 3 figure
Antiresonance phase shift in strongly coupled cavity QED
We investigate phase shifts in the strong coupling regime of single-atom
cavity quantum electrodynamics (QED). On the light transmitted through the
system, we observe a phase shift associated with an antiresonance and show that
both its frequency and width depend solely on the atom, despite the strong
coupling to the cavity. This shift is optically controllable and reaches 140
degrees - the largest ever reported for a single emitter. Our result offers a
new technique for the characterization of complex integrated quantum circuits.Comment: 5 pages, 5 figure
Analysis of the entanglement between two individual atoms using global Raman rotations
Making use of the Rydberg blockade, we generate entanglement between two
atoms individually trapped in two optical tweezers. In this paper we detail the
analysis of the data and show that we can determine the amount of entanglement
between the atoms in the presence of atom losses during the entangling
sequence. Our model takes into account states outside the qubit basis and
allows us to perform a partial reconstruction of the density matrix describing
the two atom state. With this method we extract the amount of entanglement
between pairs of atoms still trapped after the entangling sequence and measure
the fidelity with respect to the expected Bell state. We find a fidelity
for the 62% of atom pairs remaining in the traps at
the end of the entangling sequence
Entanglement of two individual neutral atoms using Rydberg blockade
We report the generation of entanglement between two individual Rb
atoms in hyperfine ground states and which are held in
two optical tweezers separated by 4 m. Our scheme relies on the Rydberg
blockade effect which prevents the simultaneous excitation of the two atoms to
a Rydberg state. The entangled state is generated in about 200 ns using pulsed
two-photon excitation. We quantify the entanglement by applying global Raman
rotations on both atoms. We measure that 61% of the initial pairs of atoms are
still present at the end of the entangling sequence. These pairs are in the
target entangled state with a fidelity of 0.75.Comment: text revised, with additional reference
Coherent excitation of a single atom to a Rydberg state
We present the coherent excitation of a single Rubidium atom to the Rydberg
state (58d3/2) using a two-photon transition. The experimental setup is
described in detail, as well as experimental techniques and procedures. The
coherence of the excitation is revealed by observing Rabi oscillations between
ground and Rydberg states of the atom. We analyze the observed oscillations in
detail and compare them to numerical simulations which include imperfections of
our experimental system. Strategies for future improvements on the coherent
manipulation of a single atom in our settings are given
Unified model for network dynamics exhibiting nonextensive statistics
We introduce a dynamical network model which unifies a number of network
families which are individually known to exhibit -exponential degree
distributions. The present model dynamics incorporates static (non-growing)
self-organizing networks, preferentially growing networks, and (preferentially)
rewiring networks. Further, it exhibits a natural random graph limit. The
proposed model generalizes network dynamics to rewiring and growth modes which
depend on internal topology as well as on a metric imposed by the space they
are embedded in. In all of the networks emerging from the presented model we
find q-exponential degree distributions over a large parameter space. We
comment on the parameter dependence of the corresponding entropic index q for
the degree distributions, and on the behavior of the clustering coefficients
and neighboring connectivity distributions.Comment: 11 pages 8 fig
Consequences of temperature fluctuations in observables measured in high energy collisions
We review the consequences of intrinsic, nonstatistical temperature
fluctuations as seen in observables measured in high energy collisions. We do
this from the point of view of nonextensive statistics and Tsallis
distributions. Particular attention is paid to multiplicity fluctuations as a
first consequence of temperature fluctuations, to the equivalence of
temperature and volume fluctuations, to the generalized thermodynamic
fluctuations relations allowing us to compare fluctuations observed in
different parts of phase space, and to the problem of the relation between
Tsallis entropy and Tsallis distributions. We also discuss the possible
influence of conservation laws on these distributions and provide some examples
of how one can get them without considering temperature fluctuations.Comment: Revised version of the invited contribution to The European Physical
Journal A (Hadrons and Nuclei) topical issue about 'Relativistic Hydro- and
Thermodynamics in Nuclear Physics' guest eds. Tamas S. Biro, Gergely G.
Barnafoldi and Peter Va
Entanglement of two individual atoms using the Rydberg blockade
We report on our recent progress on the manipulation of single rubidium atoms
trapped in optical tweezers and the generation of entanglement between two
atoms, each individually trapped in neighboring tweezers. To create an
entangled state of two atoms in their ground states, we make use of the Rydberg
blockade mechanism. The degree of entanglement is measured using global
rotations of the internal states of both atoms. Such internal state rotations
on a single atom are demonstrated with a high fidelity.Comment: Proceeding of the 19th International Conference on Laser Spectroscopy
ICOLS 2009, 7-13 June 2009, Hokkaido, Japa
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