157 research outputs found
Photon polarization and Wigner's little group
To discuss one-photon polarization states we find an explicit form of the
Wigner's little group element in the massless case for arbitrary Lorentz
transformation. As is well known, when analyzing the transformation properties
of the physical states, only the value of the phase factor is relevant. We show
that this phase factor depends only on the direction of the momentum
and does not depend on the frequency . Finally, we use
this observation to discuss the transformation properties of the linearly
polarized photons and the corresponding reduced density matrix. We find that
they transform properly under Lorentz group.Comment: Version published in Phys. Rev. A, few typos correcte
Entangled Light in Moving Frames
We calculate the entanglement between a pair of polarization-entangled photon
beams as a function of the reference frame, in a fully relativistic framework.
We find the transformation law for helicity basis states and show that, while
it is frequency independent, a Lorentz transformation on a momentum-helicity
eigenstate produces a momentum-dependent phase. This phase leads to changes in
the reduced polarization density matrix, such that entanglement is either
decreased or increased, depending on the boost direction, the rapidity, and the
spread of the beam.Comment: 4 pages and 3 figures. Minor corrections, footnote on optimal basis
state
Carcass Characteristics Of Purebred And Crossbred Nellore Females Fed Solely Pasture
This research aimed to compare carcasses of purebred and crossbred Nellore females reared uniquely on pasture (Brachiaria decumbens and Brachiaria brizantha cv. Marandu). Breeds assessed consisted of purebred Nellore (16) and Nellore x Santa Gertrudis crossbred (16), being 32 ± 1.5 months old. All animals were slaughtered as they reached 450 kg. Crossbred females showed higher slaughter, hot and cold carcass weights and longer lengths (P < 0.05). Conversely, purebred animals attained greater carcass yields (P < 0.05). Nonetheless, crossbred females had higher primal cut weights and plate/ flank percentage (P < 0.05). Also, non-carcass components as kidneys, liver, kidney-pelvic-heart fat showed higher weights for crossbred females (P < 0.05). Thus, regarding beef cattle reared and finished exclusively on grazing areas, crossbred females (Nellore x Santa Gertrudis) may be the most profitable ones for cattle raisers, since they produce heavier slaughtering carcasses. Notwithstanding, they might be interesting for meat industry, for yielding more in prime cuts than purebreds, even if raised at the same conditions and slaughtered at same age.3764213422
Relativistic BB84, relativistic errors, and how to correct them
The Bennett-Brassard cryptographic scheme (BB84) needs two bases, at least
one of them linearly polarized. The problem is that linear polarization
formulated in terms of helicities is not a relativistically covariant notion:
State which is linearly polarized in one reference frame becomes depolarized in
another one. We show that a relativistically moving receiver of information
should define linear polarization with respect to projection of
Pauli-Lubanski's vector in a principal null direction of the Lorentz
transformation which defines the motion, and not with respect to the helicity
basis. Such qubits do not depolarize.Comment: revtex
Relativistic entanglement in single-particle quantum states using Non-Linear entanglement witnesses
In this study, the spin-momentum correlation of one massive spin-1/2 and
spin-1 particle states, which are made based on projection of a relativistic
spin operator into timelike direction is investigated. It is shown that by
using Non-Linear entanglement witnesses (NLEWs), the effect of Lorentz
transformation would decrease both the amount and the region of entanglement.Comment: 16 pages, 2 figures; to be published in Quantum Inf Process,
10.1007/s11128-011-0289-z (2011
Evolution of entanglement under echo dynamics
Echo dynamics and fidelity are often used to discuss stability in quantum
information processing and quantum chaos. Yet fidelity yields no information
about entanglement, the characteristic property of quantum mechanics. We study
the evolution of entanglement in echo dynamics. We find qualitatively different
behavior between integrable and chaotic systems on one hand and between random
and coherent initial states for integrable systems on the other. For the latter
the evolution of entanglement is given by a classical time scale. Analytic
results are illustrated numerically in a Jaynes Cummings model.Comment: 5 RevTeX pages, 3 EPS figures (one color) ; v2: considerable revision
;inequality proof omitte
On Relativistic Quantum Information Properties of Entangled Wave Vectors of Massive Fermions
We study special relativistic effects on the entanglement between either
spins or momenta of composite quantum systems of two spin-1/2 massive
particles, either indistinguishable or distinguishable, in inertial reference
frames in relative motion. For the case of indistinguishable particles, we
consider a balanced scenario where the momenta of the pair are well-defined but
not maximally entangled in the rest frame while the spins of the pair are
described by a one-parameter () family of entangled bipartite states. For
the case of distinguishable particles, we consider an unbalanced scenario where
the momenta of the pair are well-defined and maximally entangled in the rest
frame while the spins of the pair are described by a one-parameter ()
family of non-maximally entangled bipartite states. In both cases, we show that
neither the spin-spin () nor the momentum-momentum () entanglements
quantified by means of Wootters' concurrence are Lorentz invariant quantities:
the total amount of entanglement regarded as the sum of these entanglements is
not the same in different inertial moving frames. In particular, for any value
of the entangling parameters, both and -entanglements are attenuated
by Lorentz transformations and their parametric rates of change with respect to
the entanglements observed in a rest frame have the same monotonic behavior.
However, for indistinguishable (distinguishable) particles, the change in
entanglement for the momenta is (is not) the same as the change in entanglement
for spins. As a consequence, in both cases, no entanglement compensation
between spin and momentum degrees of freedom occurs.Comment: 21 pages, 8 figure
Quantum Communication in Rindler Spacetime
A state that an inertial observer in Minkowski space perceives to be the
vacuum will appear to an accelerating observer to be a thermal bath of
radiation. We study the impact of this Davies-Fulling-Unruh noise on
communication, particularly quantum communication from an inertial sender to an
accelerating observer and private communication between two inertial observers
in the presence of an accelerating eavesdropper. In both cases, we establish
compact, tractable formulas for the associated communication capacities
assuming encodings that allow a single excitation in one of a fixed number of
modes per use of the communications channel. Our contributions include a
rigorous presentation of the general theory of the private quantum capacity as
well as a detailed analysis of the structure of these channels, including their
group-theoretic properties and a proof that they are conjugate degradable.
Connections between the Unruh channel and optical amplifiers are also
discussed.Comment: v3: 44 pages, accepted in Communications in Mathematical Physic
Spin Fidelity for Three-qubit Greenberger-Horne-Zeilinger and W States Under Lorentz Transformations
Constructing the reduced density matrix for a system of three massive
spin particles described by a wave packet with Gaussian momentum
distribution and a spin part in the form of GHZ or W state, the fidelity for
the spin part of the system is investigated from the viewpoint of moving
observers in the jargon of special relativity. Using a numerical approach, it
turns out that by increasing the boost speed, the spin fidelity decreases and
reaches to a non-zero asymptotic value that depends on the momentum
distribution and the amount of momentum entanglement.Comment: 12pages, 2 figure
Finite-Temperature Transport in Finite-Size Hubbard Rings in the Strong-Coupling Limit
We study the current, the curvature of levels, and the finite temperature
charge stiffness, D(T,L), in the strongly correlated limit, U>>t, for Hubbard
rings of L sites, with U the on-site Coulomb repulsion and t the hopping
integral. Our study is done for finite-size systems and any band filling. Up to
order t we derive our results following two independent approaches, namely,
using the solution provided by the Bethe ansatz and the solution provided by an
algebraic method, where the electronic operators are represented in a
slave-fermion picture. We find that, in the U=\infty case, the
finite-temperature charge stiffness is finite for electronic densities, n,
smaller than one. These results are essencially those of spinless fermions in a
lattice of size L, apart from small corrections coming from a statistical flux,
due to the spin degrees of freedom. Up to order t, the Mott-Hubbard gap is
\Delta_{MH}=U-4t, and we find that D(T) is finite for n<1, but is zero at
half-filling. This result comes from the effective flux felt by the holon
excitations, which, due to the presence of doubly occupied sites, is
renormalized to
\Phi^{eff}=\phi(N_h-N_d)/(N_d+N_h), and which is zero at half-filling, with
N_d and N_h being the number of doubly occupied and empty lattice sites,
respectively. Further, for half-filling, the current transported by any
eigenstate of the system is zero and, therefore, D(T) is also zero.Comment: 15 pages and 6 figures; accepted for PR
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