59 research outputs found
Non-deterministic Gates for Photonic Single Rail Quantum Logic
We discuss techniques for producing, manipulating and measureing qubits
encoded optically as vacuum and single photon states. We show that a universal
set of non-deterministic gates can be constructed using linear optics and
photon counting. We investigate the efficacy of a test gate given realistic
detector efficiencies.Comment: 8 pages, 6 figure
Teleportation-based number state manipulation with number sum measurement
We examine various manipulations of photon number states which can be
implemented by teleportation technique with number sum measurement. The
preparations of the Einstein-Podolsky-Rosen resources as well as the number sum
measurement resulting in projection to certain Bell state may be done
conditionally with linear optical elements, i.e., beam splitters, phase
shifters and zero-one-photon detectors. Squeezed vacuum states are used as
primary entanglement resource, while single-photon sources are not required.Comment: 9 pages, 4 figures, Misprints are corrected. 3 figures for number sum
measurement are added. Discussion on manipulations are expanded. Calculations
for success probabilities are added. Fig.4 is adde
Evidence for geometry-dependent universal fluctuations of the Kardar-Parisi-Zhang interfaces in liquid-crystal turbulence
We provide a comprehensive report on scale-invariant fluctuations of growing
interfaces in liquid-crystal turbulence, for which we recently found evidence
that they belong to the Kardar-Parisi-Zhang (KPZ) universality class for 1+1
dimensions [Phys. Rev. Lett. 104, 230601 (2010); Sci. Rep. 1, 34 (2011)]. Here
we investigate both circular and flat interfaces and report their statistics in
detail. First we demonstrate that their fluctuations show not only the KPZ
scaling exponents but beyond: they asymptotically share even the precise forms
of the distribution function and the spatial correlation function in common
with solvable models of the KPZ class, demonstrating also an intimate relation
to random matrix theory. We then determine other statistical properties for
which no exact theoretical predictions were made, in particular the temporal
correlation function and the persistence probabilities. Experimental results on
finite-time effects and extreme-value statistics are also presented. Throughout
the paper, emphasis is put on how the universal statistical properties depend
on the global geometry of the interfaces, i.e., whether the interfaces are
circular or flat. We thereby corroborate the powerful yet geometry-dependent
universality of the KPZ class, which governs growing interfaces driven out of
equilibrium.Comment: 31 pages, 21 figures, 1 table; references updated (v2,v3); Fig.19
updated & minor changes in text (v3); final version (v4); J. Stat. Phys.
Online First (2012
Conditional generation of arbitrary multimode entangled states of light with linear optics
We propose a universal scheme for the probabilistic generation of an
arbitrary multimode entangled state of light with finite expansion in Fock
basis. The suggested setup involves passive linear optics, single photon
sources, strong coherent laser beams, and photodetectors with single-photon
resolution. The efficiency of this setup may be greatly enhanced if, in
addition, a quantum memory is available.Comment: 7 pages, 5 figure
Generation of entangled coherent states via cross phase modulation in a double electromagnetically induced transparency regime
The generation of an entangled coherent state is one of the most important
ingredients of quantum information processing using coherent states. Recently,
numerous schemes to achieve this task have been proposed. In order to generate
travelling-wave entangled coherent states, cross phase modulation, optimized by
optical Kerr effect enhancement in a dense medium in an electromagnetically
induced transparency (EIT) regime, seems to be very promising. In this
scenario, we propose a fully quantized model of a double-EIT scheme recently
proposed [D. Petrosyan and G. Kurizki, {\sl Phys. Rev. A} {\bf 65}, 33833
(2002)]: the quantization step is performed adopting a fully Hamiltonian
approach. This allows us to write effective equations of motion for two
interacting quantum fields of light that show how the dynamics of one field
depends on the photon-number operator of the other. The preparation of a
Schr\"odinger cat state, which is a superposition of two distinct coherent
states, is briefly exposed. This is based on non-linear interaction via
double-EIT of two light fields (initially prepared in coherent states) and on a
detection step performed using a beam splitter and two photodetectors.
In order to show the entanglement of a generated entangled coherent state, we
suggest to measure the joint quadrature variance of the field. We show that the
entangled coherent states satisfy the sufficient condition for entanglement
based on quadrature variance measurement. We also show how robust our scheme is
against a low detection efficiency of homodyne detectors.Comment: 15 pages, 9 figures; extensively revised version; added Section
Gravitational Lensing at Millimeter Wavelengths
With today's millimeter and submillimeter instruments observers use
gravitational lensing mostly as a tool to boost the sensitivity when observing
distant objects. This is evident through the dominance of gravitationally
lensed objects among those detected in CO rotational lines at z>1. It is also
evident in the use of lensing magnification by galaxy clusters in order to
reach faint submm/mm continuum sources. There are, however, a few cases where
millimeter lines have been directly involved in understanding lensing
configurations. Future mm/submm instruments, such as the ALMA interferometer,
will have both the sensitivity and the angular resolution to allow detailed
observations of gravitational lenses. The almost constant sensitivity to dust
emission over the redshift range z=1-10 means that the likelihood for strong
lensing of dust continuum sources is much higher than for optically selected
sources. A large number of new strong lenses are therefore likely to be
discovered with ALMA, allowing a direct assessment of cosmological parameters
through lens statistics. Combined with an angular resolution <0.1", ALMA will
also be efficient for probing the gravitational potential of galaxy clusters,
where we will be able to study both the sources and the lenses themselves, free
of obscuration and extinction corrections, derive rotation curves for the
lenses, their orientation and, thus, greatly constrain lens models.Comment: 69 pages, Review on quasar lensing. Part of a LNP Topical Volume on
"Dark matter and gravitational lensing", eds. F. Courbin, D. Minniti. To be
published by Springer-Verlag 2002. Paper with full resolution figures can be
found at ftp://oden.oso.chalmers.se/pub/tommy/mmviews.ps.g
Human Resource Flexibility as a Mediating Variable Between High Performance Work Systems and Performance
Much of the human resource management literature has demonstrated the impact of high performance
work systems (HPWS) on organizational performance. A new generation of studies is
emerging in this literature that recommends the inclusion of mediating variables between HPWS
and organizational performance. The increasing rate of dynamism in competitive environments
suggests that measures of employee adaptability should be included as a mechanism that may
explain the relevance of HPWS to firm competitiveness. On a sample of 226 Spanish firms, the
studyâs results confirm that HPWS influences performance through its impact on the firmâs
human resource (HR) flexibility
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