8,768 research outputs found
THE APM CLUSTER SURVEY: CLUSTER DETECTION AND LARGE-SCALE STRUCTURE
The APM Cluster Survey was based on a modification of Abell's original
classification scheme for galaxy clusters. Here we discuss the results of an
investigation of the stability of the statistical properties of the cluster
catalogue to changes in the selection parameters. For a poor choice of
selection parameters we find clear indications of line-of-sight clusters, but
there is a wide range of input parameters for which the statistical properties
of the catalogue are stable. We conclude that clusters selected in this way are
indeed useful as tracers of large-scale structure.Comment: to appear in Proceedings of the XXXth Moriond Conference. 4 pages,
gzipped, uuencoded postscript (inc. 2 figures
The CGLMP Bell Inequalities and Quantum Theory
Quantum non-locality tests have been of interest since the original EPR
paper. The present paper discusses whether the CGLMP (Bell) inequalities
obtained by Collins et al are possible tests for showing that quantum theory is
not underpinned by local hidden variable theory (LHVT). It is found by applying
Fine's theorem that the CGLMP approach involves a LHVT for the probabilities
associated with measurements on two observables (each from one of the two
sub-subsystems), even though the underlying probabilities for measurements of
all four observables involve a hidden variable theory which is not required to
be local. Although the CGLMP inequalities involve probabilities for
measurements of one observable per sub-system and are compatible with the
Heisenberg uncertainty principle, there is no unambiguous quantum measurement
process linked to the probabilities in the CGLMP inequalities. Quantum
measurements corresponding to the different classical measurements that give
the same CGLMP probability are found to yield different CGLMP probabilities.
However, violation of a CGLMP inequality based on any one of the possible
quantum measurement sequences is sufficient to show that the Collins et al LHVT
does not predict the same results as quantum theory. This is found to occur for
a state considered in their paper - though for observables whose physical
interpretation is unclear. In spite of the problems of comparing the HVT
inequalities with quantum expressions, it is concluded that the CGLMP
inequalities are indeed suitable for ruling out local hidden variable theories.
The state involved could apply to a macroscopic system, so the CGLMP Bell
inequalities are important for finding cases of macroscopic violations of Bell
locality. Possible experiments in double-well Bose condensates involving atoms
with two hyperfine components are discussed.Comment: 23 pages, 0 figures. Version 4. Significant revision of previous
version. Relation of CGLMP inequalities to local hidden variable theories
demonstrated via Fine's theore
Theory of decoherence in Bose-Einstein condensate interferometry
A full treatment of decoherence and dephasing effects in BEC interferometry
has been developed based on using quantum correlation functions for treating
interferometric effects. The BEC is described via a phase space distribution
functional of the Wigner type for the condensate modes and the positive P type
for the non-condensate modes. Ito equations for stochastic condensate and
non-condensate field functions replace the functional Fokker-Planck equation
for the distribution functional and stochastic averages of field function
products determine the quantum correlation functions.Comment: Proceedings DICE 06 Conference, 11-15 Sept 2006, Piombino, Ital
Theory of decoherence in Bose-Einstein condensate interferometry
A full treatment of decoherence and dephasing effects in BEC interferometry
has been developed based on using quantum correlation functions for treating
interferometric effects. The BEC is described via a phase space distribution
functional of the Wigner type for the condensate modes and the positive P type
for the non-condensate modes. Ito equations for stochastic condensate and
non-condensate field functions replace the functional Fokker-Planck equation
for the distribution functional and stochastic averages of field function
products determine the quantum correlation functions.Comment: Proceedings DICE 06 Conference, 11-15 Sept 2006, Piombino, Ital
Theory of decoherence in Bose-Einstein condensate interferometry
A full treatment of decoherence and dephasing effects in BEC interferometry
has been developed based on using quantum correlation functions for treating
interferometric effects. The BEC is described via a phase space distribution
functional of the Wigner type for the condensate modes and the positive P type
for the non-condensate modes. Ito equations for stochastic condensate and
non-condensate field functions replace the functional Fokker-Planck equation
for the distribution functional and stochastic averages of field function
products determine the quantum correlation functions.Comment: Proceedings DICE 06 Conference, 11-15 Sept 2006, Piombino, Ital
Cascade atom in high-Q cavity: The spectrum for non-Markovian decay
The spontaneous emission spectrum for a three level cascade configuration
atom in a single mode high-Q cavity coupled to a zero temperature reservoir of
continuum external modes is determined from the atom-cavity mode master
equation using the quantum regression theorem. Initially the atom is in its
upper state and the cavity mode empty of photons. Following Glauber, the
spectrum is defined via the response of a detector atom. Spectra are calculated
for the detector located inside the cavity (case A), outside the cavity end
mirror (Case B-end emission), or placed for emission out the side of the cavity
(Case C). The spectra for case A and case B are found to be essentially the
same. In all the cases the predicted lineshapes are free of instrumental
effects and only due to cavity decay. Spectra are presented for intermediate
and strong coupling regime situations (where both atomic transitions are
resonant with the cavity frequency), for cases of non-zero cavity detuning, and
for cases where the two atomic transition frequencies differ. The spectral
features for Cases B(A) and C are qualitatively similar, with six spectral
peaks for resonance cases and eight for detuned cases. These general features
of the spectra can be understood via the dressed atom model. However, Case B
and C spectra differ in detail, with the latter exhibiting a deep spectral hole
at the cavity frequency due to quantum interference effects.Comment: 29 pages, 14 figures; v2: very minor correction to two equations,
thicker lines in some figure
On the CCD Calibration of Zwicky galaxy magnitudes & The Properties of Nearby Field Galaxies
We present CCD photometry for galaxies around 204 bright (m_Z < 15.5) Zwicky
galaxies in the equatorial extension of the APM Galaxy Survey, sampling and
area over 400 square degrees, which extends 6 hours in right ascension. We fit
a best linear relation between the Zwicky magnitude system, m_Z, and the CCD
photometry, B, by doing a likehood analysis that corrects for Malmquist bias.
This fit yields a mean scale error in Zwicky of 0.38 mag per magnitude: ie
Delta m_Z = (0.62 \pm 0.05) Delta B and a mean zero point of = -0.35
\pm 0.15 mag. The scatter around this fit is about 0.4 mag. Correcting the
Zwicky magnitude system with the best fit model results in a 60% lower
normalization and 0.35 mag brighter M_* in the luminosity function. This brings
the CfA2 luminosity function closer to the other low redshift estimations (eg
Stromlo-APM or LCRS). We find a significant positive angular correlation of
magnitudes and position in the sky at scales smaller than about 5 armin, which
corresponds to a mean separation of 120 Kpc/h. We also present colours, sizes
and ellipticities for galaxies in our fields which provides a good local
reference for the studies of galaxy evolution.Comment: Full size figures can be found in
http://www.ieec.fcr.es/cosmo-www/zwicky.ps Version accepted for publication
in MNRAS. Extended discussion on properties of nearby galaxies. References
added. An inconsistency in the R band isophote used has been corrected. Main
results and conclusions are unchange
Field Quantization, Photons and Non-Hermitean Modes
Field quantization in three dimensional unstable optical systems is treated
by expanding the vector potential in terms of non-Hermitean (Fox-Li) modes in
both the cavity and external regions. The cavity non-Hermitean modes (NHM) are
treated using the paraxial and monochromaticity approximations. The NHM
bi-orthogonality relationships are used in a standard canonical quantization
procedure based on introducing generalised coordinates and momenta for the
electromagnetic (EM) field. The quantum EM field is equivalent to a set of
quantum harmonic oscillators (QHO), associated with either the cavity or the
external region NHM. This confirms the validity of the photon model in unstable
optical systems, though the annihilation and creation operators for each QHO
are not Hermitean adjoints. The quantum Hamiltonian for the EM field is the sum
of non-commuting cavity and external region contributions, each of which is sum
of independent QHO Hamiltonians for each NHM, but the external field
Hamiltonian also includes a coupling term responsible for external NHM photon
exchange processes. Cavity energy gain and loss processes is associated with
the non-commutativity of cavity and external region operators, given in terms
of surface integrals involving cavity and external region NHM functions on the
cavity-external region boundary. The spontaneous decay of a two-level atom
inside an unstable cavity is treated using the essential states approach and
the rotating wave approximation. Atomic transitions leading to cavity NHM
photon absorption have a different coupling constant to those leading to photon
emission, a feature resulting from the use of NHM functions. Under certain
conditions the decay rate is enhanced by the Petermann factor.Comment: 38 pages, tex, 2 figures, ps. General expression for decay rate
added. To be published in Journal of Modern Optic
New spin squeezing and other entanglement tests for two mode systems of identical bosons
For any quantum state representing a physical system of identical particles, the density operator must satisfy the symmetrization principle (SP) and conform to super-selection rules (SSR) that prohibit coherences between differing total particle numbers. Here we consider bi-partitite states for massive bosons, where both the system and sub-systems are modes (or sets of modes) and particle numbers for quantum states are determined from the mode occupancies. Defining non-entangled or separable states as those prepared via local operations (on the sub-systems) and classical communication processes, the sub-system density operators are also required to satisfy the SP and conform to the SSR, in contrast to some other approaches. Whilst in the presence of this additional constraint the previously obtained sufficiency criteria for entanglement, such as the sum of the ˆSx and ˆSy variances for the Schwinger spin components being less than half the mean boson number, and the strong correlation test of |haˆm (bˆ†)ni|2 being greater than h(aˆ†)maˆm (bˆ†)nbˆni(m, n = 1, 2, . . .) are still valid, new tests are obtained in our work. We show that the presence of spin squeezing in at least one of the spin components ˆSx , ˆSy and ˆSz is a sufficient criterion for the presence of entanglement and a simple correlation test can be constructed of |haˆm (bˆ†)ni|2 merely being greater than zero.We show that for the case of relative phase eigenstates, the new spin squeezing test for entanglement is satisfied (for the principle spin operators), whilst the test involving the sum of the ˆSx and ˆSy variances is not. However, another spin squeezing entanglement test for Bose–Einstein condensates involving the variance in ˆSz being less than the sum of the squared mean values for ˆSx and ˆSy divided by the boson number was based on a concept of entanglement inconsistent with the SP, and here we present a revised treatment which again leads to spin squeezing as an entanglement test
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