16,201 research outputs found
Mixedness and teleportation
We show that on exceeding a certain degree of mixedness (as quantified by the
von Neumann entropy), entangled states become useless for teleporatation. By
increasing the dimension of the entangled systems, this entropy threshold can
be made arbitrarily close to maximal. This entropy is found to exceed the
entropy threshold sufficient to ensure the failure of dense coding.Comment: 6 pages, no figure
Building multiparticle states with teleportation
We describe a protocol which can be used to generate any N-partite pure
quantum state using Einstein-Podolsky-Rosen (EPR) pairs. This protocol employs
only local operations and classical communication between the N parties
(N-LOCC). In particular, we rely on quantum data compression and teleportation
to create the desired state. This protocol can be used to obtain upper bounds
for the bipartite entanglement of formation of an arbitrary N-partite pure
state, in the asymptotic limit of many copies. We apply it to a few
multipartite states of interest, showing that in some cases it is not optimal.
Generalizations of the protocol are developed which are optimal for some of the
examples we consider, but which may still be inefficient for arbitrary states.Comment: 11 pages, 1 figure. Version 2 contains an example for which protocol
P3 is better than protocol P2. Correction to references in version
Method of convex rigid frames and applications in studies of multipartite quNit pure-states
In this Letter we suggest a method of convex rigid frames in the studies of
the multipartite quNit pure-states. We illustrate what are the convex rigid
frames and what is the method of convex rigid frames. As the applications we
use this method to solve some basic problems and give some new results (three
theorems): The problem of the partial separability of the multipartite quNit
pure-states and its geometric explanation; The problem of the classification of
the multipartite quNit pure-states, and give a perfect explanation of the local
unitary transformations; Thirdly, we discuss the invariants of classes and give
a possible physical explanation.Comment: 6 pages, no figur
Bounds on relative entropy of entanglement for multi-party systems
We present upper and lower bounds to the relative entropy of entanglement of
multi-party systems in terms of the bi-partite entanglements of formation and
distillation and entropies of various subsystems. We point out implications of
our results to the local reversible convertibility of multi-party pure states
and discuss their physical basis in terms of deleting of information.Comment: 4 pages, no figure
F(750), We Miss You as a Bound State of 6 Top and 6 Antitop Quarks, Multiple Point Principle
We review our speculation, that in the pure Standard Model the exchange of
Higgses, including also the ones "eaten by and Z", and of gluons
together make a bound state of 6 top plus 6 anti top quarks bind so strongly
that its mass gets down to about 1/3 of the mass of the collective mass 12
of the 12 constituent quarks. The true importance of this speculated
bound state is that it makes it possible to uphold, even inside the Standard
Mode, our proposal for what is really a new law of nature saying that there are
several phases of empty space, vacua, all having very small energy densities
(of the order of the present energy density in the universe). The reason
suggested for believing in this new law called the "Multiple (Criticality)
Point Principle" is, that estimating the mass of the speculated bound state
using the "Multiple Point Principle" leads to two consistent mass-values; and
they even agree with a crude bag-model like estimate of the mass of this bound
state. Very, unfortunately, the statistical fluctuation so popular last year,
when interpreted as the digamma resonance F(750), turned out not to be a real
resonance, because our estimated bound state mass is just around the mass of
750 GeV.Comment: 25 pages, 11 figures, Corfu Summer Institute 2016 "School and
Workshops on Elementary Particle Physics and Gravity", 31 August - 23
September, 2016, Corfu, Greec
Solar System experiments do not yet veto modified gravity models
The dynamical equivalence between modified and scalar-tensor gravity theories
is revisited and it is concluded that it breaks down in the limit to general
relativity. A gauge-independent analysis of cosmological perturbations in both
classes of theories lends independent support to this conclusion. As a
consequence, the PPN formalism of scalar-tensor gravity and Solar System
experiments do not veto modified gravity, as previously thought.Comment: 7 pages, latex, submitted to Phys. Rev.
Quantum cobwebs: Universal entangling of quantum states
Entangling an unknown qubit with one type of reference state is generally
impossible. However, entangling an unknown qubit with two types of reference
states is possible. To achieve this, we introduce a new class of states called
zero sum amplitude (ZSA) multipartite, pure entangled states for qubits and
study their salient features. Using shared-ZSA state, local operation and
classical communication we give a protocol for creating multipartite entangled
states of an unknown quantum state with two types of reference states at remote
places. This provides a way of encoding an unknown pure qubit state into a
multiqubit entangled state. We quantify the amount of classical and quantum
resources required to create universal entangled states. This is possibly a
strongest form of quantum bit hiding with multiparties.Comment: Invited talk in II Winter Institute on FQTQO: Quantum Information
Processing, held at S. N. Bose Center for Basic Science, Kolkata, during Jan
2-11, 2002. (To appear in Pramana-J. of Physics, 2002.
Multipartite entanglement in 2 x 2 x n quantum systems
We classify multipartite entangled states in the 2 x 2 x n (n >= 4) quantum
system, for example the 4-qubit system distributed over 3 parties, under local
filtering operations. We show that there exist nine essentially different
classes of states, and they give rise to a five-graded partially ordered
structure, including the celebrated Greenberger-Horne-Zeilinger (GHZ) and W
classes of 3 qubits. In particular, all 2 x 2 x n-states can be
deterministically prepared from one maximally entangled state, and some
applications like entanglement swapping are discussed.Comment: 9 pages, 3 eps figure
Asymmetric universal entangling machine
We give a definition of asymmetric universal entangling machine which
entangles a system in an unknown state to a specially prepared ancilla. The
machine produces a fixed state-independent amount of entanglement in exchange
to a fixed degradation of the system state fidelity. We describe explicitly
such a machine for any quantum system having levels and prove its
optimality. We show that a -dimensional ancilla is sufficient for reaching
optimality. The introduced machine is a generalization to a number of widely
investigated universal quantum devices such as the symmetric and asymmetric
quantum cloners, the symmetric quantum entangler, the quantum information
distributor and the universal-NOT gate.Comment: 28 pages, 3 figure
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