34,478 research outputs found
Entropy Bound for the Classical Capacity of a Quantum Channel Assisted by Classical Feedback
We prove that the classical capacity of an arbitrary quantum channel assisted
by a free classical feedback channel is bounded from above by the maximum
average output entropy of the quantum channel. As a consequence of this bound,
we conclude that a classical feedback channel does not improve the classical
capacity of a quantum erasure channel, and by taking into account energy
constraints, we conclude the same for a pure-loss bosonic channel. The method
for establishing the aforementioned entropy bound involves identifying an
information measure having two key properties: 1) it does not increase under a
one-way local operations and classical communication channel from the receiver
to the sender and 2) a quantum channel from sender to receiver cannot increase
the information measure by more than the maximum output entropy of the channel.
This information measure can be understood as the sum of two terms, with one
corresponding to classical correlation and the other to entanglement.Comment: v2: 6 pages, 1 figure, final version published in conference
proceeding
Lepton flavor violating and conversion in unparticle physics
We have studied lepton flavor violation processes and
conversion in nuclei induced by unparticle. Both and conversion rate strongly
depend on the scale dimension and the unparticle coupling
(K=V, A, S, P). Present experimental upper bounds on
, and put stringent constraints on the parameters of unaprticle physics. The
scale dimensions around 2 are favored for the unparticle scale
of and the unparticle coupling of
. is proportional to
for the pure vector and scalar couplings between
unparticle and SM fermions, this peculiar atomatic number dependence can be
used to distinguish unparticle from other theoretical models.Comment: 16 pages, 5 figure
Variational Derivation of Relativistic Fermion-Antifermion Wave Equations in QED
We present a variational method for deriving relativistic two-fermion wave
equations in a Hamiltonian formulation of QED. A reformulation of QED is
performed, in which covariant Green functions are used to solve for the
electromagnetic field in terms of the fermion fields. The resulting modified
Hamiltonian contains the photon propagator directly. The reformulation permits
one to use a simple Fock-space variational trial state to derive relativistic
fermion-antifermion wave equations from the corresponding quantum field theory.
We verify that the energy eigenvalues obtained from the wave equation agree
with known results for positronium.Comment: 25 pages, accepted in Journal of Mathematical Physics (2004
Three realizations of quantum affine algebra
In this article we establish explicit isomorphisms between three realizations
of quantum twisted affine algebra : the Drinfeld ("current")
realization, the Chevalley realization and the so-called realization,
investigated by Faddeev, Reshetikhin and Takhtajan.Comment: 15 page
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