10,214 research outputs found
Entanglement, BEC, and superfluid-like behavior of two-mode photon systems
A system of two interacting photon modes, without constraints on the photon
number, in the presence of a Kerr nonlinearity, exhibits BEC if the transfer
amplitude is greater than the mode frequency. A symmetry-breaking field (SBF)
can be introduced by taking into account a classical electron current. The
ground state, in the limit of small nonlinearity, becomes a squeezed state, and
thus the modes become entangled. The smaller is the SBF, the greater is
entanglement. Superfluid-like behavior is observed in the study of entanglement
growth from an initial coherent state, since in the short-time range the growth
does not depend on the SBF amplitude, and on the initial state amplitude. On
the other hand, the latter is the only parameter which determines entanglement
in the absence of the SBF
Teleportation on a quantum dot array
We present a model of quantum teleportation protocol based on a double
quantum dot array. The unknown qubit is encoded using a pair of quantum dots,
coupled by tunneling, with one excess electron. It is shown how to create
maximally entangled states with this kind of qubits using an adiabatically
increasing Coulomb repulsion between different pairs. This entangled states are
exploited to perform teleportation again using an adiabatic coupling between
them and the incoming unknown state. Finally, a sudden separation of Bob's
qubit enables a time evolution of Alice's state providing a modified version of
standard Bell measurement. Substituting the four quantum dots entangled state
with a chain of coupled DQD's, a quantum channel with high fidelity arises from
this scheme allowing the transmission over long distances.Comment: 4 pages, 2 figure
Dark Radiation or Warm Dark Matter from long lived particle decays in the light of Planck
Although Planck data supports the standard \Lambda CDM model, it still allows
for the presence of Dark Radiation corresponding up to about half an extra
standard neutrino species. We propose a scenario for obtaining a fractional
"effective neutrino species" from a thermally produced particle which decays
into a much lighter stable relic plus standard fermions. At lifetimes much
longer than 1 sec, both the relic particles and the non-thermal neutrino
component contribute to Dark Radiation. By increasing the stable-to-unstable
particle mass ratio, the relic particle no longer acts as Dark Radiation but
instead becomes a candidate for Warm Dark Matter with mass O(1keV - 100GeV). In
both cases it is possible to address the lithium problem.Comment: 18 pages, 2 figures; v3 matches version to be published in PL
Nonlinear Relaxation in Population Dynamics
We analyze the nonlinear relaxation of a complex ecosystem composed of many
interacting species. The ecological system is described by generalized
Lotka-Volterra equations with a multiplicative noise. The transient dynamics is
studied in the framework of the mean field theory and with random interaction
between the species. We focus on the statistical properties of the asymptotic
behaviour of the time integral of the i-th population and on the distribution
of the population and of the local field.Comment: 11 pages, 4 figures, in press in Int. Journal of Fractals (2001
Selective writing and read-out of a register of static qubits
We propose a setup comprising an arbitrarily large array of static qubits
(SQs), which interact with a flying qubit (FQ). The SQs work as a quantum
register, which can be written or read-out by means of the FQ through quantum
state transfer (QST). The entire system, including the FQ's motional degrees of
freedom, behaves quantum mechanically. We demonstrate a strategy allowing for
selective QST between the FQ and a single SQ chosen from the register. This is
achieved through a perfect mirror located beyond the SQs and suitable
modulation of the inter-SQ distances.Comment: 14 pages, 4 figure
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