40,743 research outputs found
Fisher information in quantum statistics
Braunstein and Caves (1994) proposed to use Helstrom's {\em quantum
information} number to define, meaningfully, a metric on the set of all
possible states of a given quantum system. They showed that the quantum
information is nothing else than the maximal Fisher information in a
measurement of the quantum system, maximized over all possible measurements.
Combining this fact with classical statistical results, they argued that the
quantum information determines the asymptotically optimal rate at which
neighbouring states on some smooth curve can be distinguished, based on
arbitrary measurements on identical copies of the given quantum system.
We show that the measurement which maximizes the Fisher information typically
depends on the true, unknown, state of the quantum system. We close the
resulting loophole in the argument by showing that one can still achieve the
same, optimal, rate of distinguishability, by a two stage adaptive measurement
procedure.
When we consider states lying not on a smooth curve, but on a manifold of
higher dimension, the situation becomes much more complex. We show that the
notion of ``distinguishability of close-by states'' depends strongly on the
measurement resources one allows oneself, and on a further specification of the
task at hand. The quantum information matrix no longer seems to play a central
role.Comment: This version replaces the previous versions of February 1999 (titled
'An Example of Non-Attainability of Expected Quantum Information') and that
of November 1999. Proofs and results are much improved. To appear in J. Phys.
Multiple point principle as a mechanism for the suppression of FCNC and CP--violation phenomena in the 2HDM
We argue that multiple point principle (MPP) can be used to ensure CP
conservation and the absence of flavour changing neutral currents within the
two Higgs doublet model (2HDM). We also discuss Higgs phenomenology in the MPP
inspired 2HDM.Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTeX, 2 eps
figures,CERN preprint number added, references update
Fixed point scenario in the Two Higgs Doublet Model inspired by degenerate vacua
We consider the renormalisation group flow of Higgs and Yukawa couplings
within the simplest non--supersymmetric two Higgs doublet extension of the
Standard Model (SM). In this model the couplings are adjusted so that the
multiple point principle (MPP) assumption, which implies the existence of a
large set of degenerate vacua at some high energy scale , is realised.
When the top quark Yukawa coupling at the scale is large, the
solutions of RG equations in this MPP inspired 2 Higgs Doublet Model (2HDM)
converge to quasi--fixed points. We analyse the Higgs spectrum and couplings in
the quasi--fixed point scenario and compute a theoretical upper bound on the
lightest Higgs boson mass. When the scale is low, the coupling of the
SM--like Higgs scalar to the top quark can be significantly larger in the
considered model than in the SM, resulting in the enhanced production of Higgs
bosons at the LHC.Comment: 16 pages, 3 figures, CERN preprint number added, references update
Results of bottom trawl surveys carried out in Vietnamese waters (20-200 m) in 1996-1997
Bottom trawl surveys were conducted in the southwest monsoon season in 1996 (survey 1) and in the northeast monsoon season in 1996-97 (survey 2) throughout Vietnamese waters. The surveys mainly covered the depth zone 50-200 m but in the northeast monsoon season the depth zone 20-50 m was included in the northern and southern areas. Overall, 273 trawl hauls were conducted. The total biomass for Vietnamese waters in the depth zone 20-200 m was estimated at 700 000 t . Biomass estimates are given for the most abundant species. A relatively higher mean catch-per-unit effort (CPUE) was obtained from survey 2 than from survey 1 and in partcular at depth ranges 50-100 and 100-200 m in south Vietnam. Overall, the dominant families were Monacanthidae (34%), Carangidae (15%), Trichiuridae (9%) and Synodontidae (6%)
On the Smallness of the Cosmological Constant in SUGRA Models Inspired by Degenerate Vacua
In the no-scale supergravity global symmetries protect local supersymmetry
and a zero value for the cosmological constant. The breakdown of these
symmetries, which ensures the vanishing of the vacuum energy density, results
in a set of degenerate vacua with broken and unbroken supersymmetry leading to
the natural realisation of the multiple point principle (MPP). In the MPP
inspired SUGRA models the cosmological constant is naturally tiny.Comment: Parallel talk at SUSY09, Boston, USA, June 2009, 5 page
The one-way CNOT simulation
In this paper we present the complete simulation of the quantum logic CNOT
gate in the one-way model, that consists entirely of one-qubit measurements on
a particular class of entangled states.Comment: 7 pages, 2 figure
Can the X(3872) be a 1^{++} four-quark state?
We use QCD spectral sum rules to test the nature of the meson X(3872),
assumed to be an exotic four-quark (c\bar{c}q\bar{q}) state with J^{PC}=1^{++}.
For definiteness, we work with the current proposed recently by Maiani et al
[1], at leading order in \alpha_s, consider the contributions of higher
dimension condensates and keep terms which are linear in the light quark mass
m_q. We find M_X=(3925+- 127) MeV which is compatible, within the errors, with
he experimental candidate X(3872), while the SU(3) breaking-terms lead to an
unusual mass-splitting M_{X^{s}}-M_X=- (61+-30) MeV. The mass-difference
between the neutral states due to isospin violation of about (2.6-3.9) MeV is
much smaller than the value (8+-3) MeV proposed in [1]. For the b-quark, we
predict M_{X_b}= (10144+-106) MeV for the X_b(b\bar{b}q \bar{q}), which is much
below the {\bar B}B* threshold in contrast to the {\bar B}B* molecule
prediction [2], and for the X_b^s(b\bar{b}s \bar{s}), a mass-splitting
M_{X^s_{b}}-M_{X_b}=-(121+-182) MeV. Our analysis also indicates that the
mass-splitting between the ground state and the radial excitation of about
(225~250) MeV is much smaller than in the case of ordinary mesons and is
(within the errors) flavour-independent. We also extract the decay constants,
analogous to f_\pi, of such mesons, which are useful for further studies of
their leptonic and hadronic decay widths. The uncertainties of our estimates
are mainly due to the ones from the c and b quark masses.Comment: 16 pages, 10 figures. Version to appear in Phys. Rev.
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