20,362 research outputs found
Search for Lorentz Violation in a Short-Range Gravity Experiment
An experimental test of the Newtonian inverse square law at short range has
been used to set limits on Lorentz violation in the pure gravity sector of the
Standard-Model Extension. On account of the planar test mass geometry,
nominally null with respect to inverse square forces, the limits derived for
the SME coefficients of Lorentz violation are on the order s ~ 10000.Comment: Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28-July 2, 201
Entanglement sharing among qudits
Consider a system consisting of n d-dimensional quantum particles (qudits),
and suppose that we want to optimize the entanglement between each pair. One
can ask the following basic question regarding the sharing of entanglement:
what is the largest possible value Emax(n,d) of the minimum entanglement
between any two particles in the system? (Here we take the entanglement of
formation as our measure of entanglement.) For n=3 and d=2, that is, for a
system of three qubits, the answer is known: Emax(3,2) = 0.550. In this paper
we consider first a system of d qudits and show that Emax(d,d) is greater than
or equal to 1. We then consider a system of three particles, with three
different values of d. Our results for the three-particle case suggest that as
the dimension d increases, the particles can share a greater fraction of their
entanglement capacity.Comment: 4 pages; v2 contains a new result for 3 qudits with d=
Entanglement splitting of pure bipartite quantum states
The concept of entanglement splitting is introduced by asking whether it is
possible for a party possessing half of a pure bipartite quantum state to
transfer some of his entanglement with the other party to a third party. We
describe the unitary local transformation for symmetric and isotropic splitting
of a singlet into two branches that leads to the highest entanglement of the
output. The capacity of the resulting quantum channels is discussed. Using the
same transformation for less than maximally entangled pure states, the
entanglement of the resulting states is found. We discuss whether they can be
used to do teleportation and to test the Bell inequality. Finally we generalize
to entanglement splitting into more than two branches.Comment: 6 pages, 2 figures, extended version, to be published in Phys. Rev.
Extracting Classical Correlations from a Bipartite Quantum System
In this paper we discuss the problem of splitting the total correlations for
a bipartite quantum state described by the Von Neumann mutual information into
classical and quantum parts. We propose a measure of the classical correlations
as the difference between the Von Neumann mutual information and the relative
entropy of entanglement. We compare this measure with different measures
proposed in the literature.Comment: 5 pages, 1 figur
Quantum secret sharing
Secret sharing is a procedure for splitting a message into several parts so
that no subset of parts is sufficient to read the message, but the entire set
is. We show how this procedure can be implemented using GHZ states. In the
quantum case the presence of an eavesdropper will introduce errors so that his
presence can be detected. We also show how GHZ states can be used to split
quantum information into two parts so that both parts are necessary to
reconstruct the original qubit.Comment: 6 pages, revtex, revised version, to appear in Phys. Rev.
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
On Multipartite Pure-State Entanglement
We show that pure states of multipartite quantum systems are multiseparable
(i.e. give separable density matrices on tracing any party) if and only if they
have a generalized Schmidt decomposition. Implications of this result for the
quantification of multipartite pure-state entanglement are discussed. Further,
as an application of the techniques used here, we show that any purification of
a bipartite PPT bound entangled state is tri-inseparable, i.e. has none of its
three bipartite partial traces separable.Comment: 8 Pages ReVTeX, 4 figures (eps); v2: Revised terminology, added two
references and other minor changes; v3: Minor changes, added two references,
added author's middle initial; v4: One footnote remove
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
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