20,413 research outputs found
Discrete entanglement distribution with squeezed light
We show how one can entangle distant atoms by using squeezed light.
Entanglement is obtained in steady state, and can be increased by manipulating
the atoms locally. We study the effects of imperfections, and show how to scale
up the scheme to build a quantum network.Comment: 5 pages, 4 figure
Reduction of noise in gyro outputs
Technique is described to reduce extraneous gyro output signals by using relatively inexpensive shrouds which do not increase power comsumption. Shrouds reduce noise by minimizing mass of gas spinning with rotor, reducing Reynolds number near rotor, and inducing laminar flow
Semidirect product of CCR and CAR algebras and asymptotic states in quantum electrodynamics
A C*-algebra containing the CCR and CAR algebras as its subalgebras and
naturally described as the semidirect product of these algebras is discussed. A
particular example of this structure is considered as a model for the algebra
of asymptotic fields in quantum electrodynamics, in which Gauss' law is
respected. The appearence in this algebra of a phase variable related to
electromagnetic potential leads to the universal charge quantization.
Translationally covariant representations of this algebra with energy-momentum
spectrum in the future lightcone are investigated. It is shown that vacuum
representations are necessarily nonregular with respect to total
electromagnetic field. However, a class of translationally covariant,
irreducible representations is constructed excplicitly, which remain as close
as possible to the vacuum, but are regular at the same time. The spectrum of
energy-momentum fills the whole future lightcone, but there are no vectors with
energy-momentum lying on a mass hyperboloid or in the origin.Comment: 42 pages, LaTeX; minor corrections, a reference adde
Local unitary equivalence and entanglement of multipartite pure states
The necessary and sufficient conditions for the equivalence of arbitrary
n-qubit pure quantum states under Local Unitary (LU) operations derived in [B.
Kraus Phys. Rev. Lett. 104, 020504 (2010)] are used to determine the different
LU-equivalence classes of up to five-qubit states. Due to this classification
new parameters characterizing multipartite entanglement are found and their
physical interpretation is given. Moreover, the method is used to derive
examples of two n-qubit states (with n>2 arbitrary) which have the properties
that all the entropies of any subsystem coincide, however, the states are
neither LU-equivalent nor can be mapped into each other by general local
operations and classical communication
Local unitary equivalence of multipartite pure states
Necessary and sufficient conditions for the equivalence of arbitrary n-qubit
pure quantum states under Local Unitary (LU) operations are derived. First, an
easily computable standard form for multipartite states is introduced. Two
generic states are shown to be LU-equivalent iff their standard forms coincide.
The LU-equivalence problem for non--generic states is solved by presenting a
systematic method to determine the LU operators (if they exist) which
interconvert the two states.Comment: 5 page
Particle production in p-p collisions at sqrt(s) = 17 GeV within the statistical model
A thermal-model analysis of particle production of p-p collisions at sqrt(s)
= 17 GeV using the latest available data is presented. The sensitivity of model
parameters on data selections and model assumptions is studied. The system-size
dependence of thermal parameters and recent differences in the statistical
model analysis of p-p collisions at the super proton synchrotron (SPS) are
discussed. It is shown that the temperature and strangeness undersaturation
factor depend strongly on kaon yields which at present are still not well known
experimentally. It is conclude, that within the presently available data at the
SPS it is rather unlikely that the temperature in p-p collisions exceeds
significantly that expected in central collisions of heavy ions at the same
energy.Comment: 6 pages, 3 figures, submitted to Phys. Rev.
A time-dependent variational principle for dissipative dynamics
We extend the time-dependent variational principle to the setting of
dissipative dynamics. This provides a locally optimal (in time) approximation
to the dynamics of any Lindblad equation within a given variational manifold of
mixed states. In contrast to the pure-state setting there is no canonical
information geometry for mixed states and this leads to a family of possible
trajectories --- one for each information metric. We focus on the case of the
operationally motivated family of monotone riemannian metrics and show further,
that in the particular case where the variational manifold is given by the set
of fermionic gaussian states all of these possible trajectories coincide. We
illustrate our results in the case of the Hubbard model subject to spin
decoherence.Comment: Published versio
A probabilistic and information theoretic interpretation of quantum evolutions
In quantum mechanics, outcomes of measurements on a state have a
probabilistic interpretation while the evolution of the state is treated
deterministically. Here we show that one can also treat the evolution as being
probabilistic in nature and one can measure `which unitary' happened. Likewise,
one can give an information-theoretic interpretation to evolutions by defining
the entropy of a completely positive map. This entropy gives the rate at which
the informational content of the evolution can be compressed. One cannot
compress this information and still have the evolution act on an unknown state,
but we demonstrate a general scheme to do so probabilistically. This allows one
to generalize super-dense coding to the sending of quantum information. One can
also define the ``interaction-entanglement'' of a unitary, and concentrate this
entanglement.Comment: 9 page
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