127 research outputs found
Phase measurements with weak reference pulses
Quantum state discrimination for two coherent states with opposite phases as
measured relative to a reference pulse is analyzed as functions of the
intensities of both the signal states and of the reference pulse. This problem
is relevant for Quantum Key Distribution with phase encoding. We consider both
the optimum measurements and simple measurements that require only
beamsplitters and photodetectors.Comment: 5 pages, 5 figures. I apologize for this boring pape
Quantum teleportation of light beams
We experimentally demonstrate quantum teleportation for continuous variables
using squeezed-state entanglement. The teleportation fidelity for a real
experimental system is calculated explicitly, including relevant imperfection
factors such as propagation losses, detection inefficiencies and phase
fluctuations. The inferred fidelity for input coherent states is F = 0.61 +-
0.02, which when corrected for the efficiency of detection by the output
observer, gives a fidelity of 0.62. By contrast, the projected result based on
the independently measured entanglement and efficiencies is 0.69. The
teleportation protocol is explained in detail, including a discussion of
discrepancy between experiment and theory, as well as of the limitations of the
current apparatus.Comment: 17 pages, 19 figures, submitted to PR
On quantum teleportation with beam-splitter-generated entanglement
Following the lead of Cochrane, Milburn, and Munro [Phys. Rev. A {\bf 62},
062307 (2000)], we investigate theoretically quantum teleportation by means of
the number-sum and phase-difference variables. We study Fock-state entanglement
generated by a beam splitter and show that two-mode Fock-state inputs can be
entangled by a beam splitter into close approximations of maximally entangled
eigenstates of the phase difference and the photon-number sum
(Einstein-Podolsky-Rosen -- EPR -- states). Such states could be experimentally
feasible with on-demand single-photon sources. We show that the teleportation
fidelity can reach near unity when such ``quasi-EPR'' states are used as the
quantum channel.Comment: 7 pages (two-column), 7 figures, submitted to Phys. Rev. A. Text
unmodified, postscript error correcte
Quantum correlated twin atomic beams via photo-dissociation of a molecular Bose-Einstein condensate
We study the process of photo-dissociation of a molecular Bose-Einstein
condensate as a potential source of strongly correlated twin atomic beams. We
show that the two beams can possess nearly perfect quantum squeezing in their
relative numbers.Comment: Corrected LaTeX file layou
Multiorder coherent Raman scattering of a quantum probe field
We study the multiorder coherent Raman scattering of a quantum probe field in
a far-off-resonance medium with a prepared coherence. Under the conditions of
negligible dispersion and limited bandwidth, we derive a Bessel-function
solution for the sideband field operators. We analytically and numerically
calculate various quantum statistical characteristics of the sideband fields.
We show that the multiorder coherent Raman process can replicate the
statistical properties of a single-mode quantum probe field into a broad comb
of generated Raman sidebands. We also study the mixing and modulation of photon
statistical properties in the case of two-mode input. We show that the prepared
Raman coherence and the medium length can be used as control parameters to
switch a sideband field from one type of photon statistics to another type, or
from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.
Study of Loschmidt Echo for a qubit coupled to an XY-spin chain environment
We study the temporal evolution of a central spin-1/2 (qubit) coupled to the
environment which is chosen to be a spin-1/2 transverse XY spin chain. We
explore the entire phase diagram of the spin-Hamiltonian and investigate the
behavior of Loschmidt echo(LE) close to critical and multicritical point(MCP).
To achieve this, the qubit is coupled to the spin chain through the anisotropy
term as well as one of the interaction terms. Our study reveals that the echo
has a faster decay with the system size (in the short time limit) close to a
MCP and also the scaling obeyed by the quasiperiod of the collapse and revival
of the LE is different in comparison to that close to a QCP. We also show that
even when approached along the gapless critical line, the scaling of the LE is
determined by the MCP where the energy gap shows a faster decay with the system
size. This claim is verified by studying the short-time and also the collapse
and revival behavior of the LE at a quasicritical point on the ferromagnetic
side of the MCP. We also connect our observation to the decoherence of the
central spin.Comment: Accepted for publication in EPJ
Character of superposed states under deterministic LOCC
In this paper we investigate the effect of superposition of states on local
conversion of pure bipartite states under deterministic LOCC. We are able to
form a bridge between comparable and incomparable classes of states through the
linear superposition of states. For example, if we consider two pairs of
incomparable states, then their superposition may result into a comparable pair
of states. We investigate many such cases and provide some of the results in
tabular form. We also investigate the entanglement behavior of such classes of
states, specifically their monotone nature. Finally we provide some bounds of
different measures of entanglement based on the idea of comparability and
incomparability under deterministic LOCC.Comment: 9 pages, pdflatex, no figure, to appear in the journal Quantum
Information Processin
Liquid crystals and their defects
These lecture notes discuss classical models of liquid crystals, and the
different ways in which defects are described according to the different
models.Comment: CIME lecture course, Cetraro, 201
Association analyses of East Asian individuals and trans-ancestry analyses with European individuals reveal new loci associated with cholesterol and triglyceride levels
Large-scale meta-analyses of genome-wide association studies (GWAS) have identified >175 loci associated with fasting cholesterol levels, including total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglycerides (TG). With differences in linkage disequilibrium (LD) structure and allele frequencies between ancestry groups, studies in additional large samples may detect new associations. We conducted staged GWAS meta-analyses in up to 69,414 East Asian individuals from 24 studies with participants from Japan, the Philippines, Korea, China, Singapore, and Taiwan. These meta-analyses identified (P < 5 × 10-8) three novel loci associated with HDL-C near CD163-APOBEC1 (P = 7.4 × 10-9), NCOA2 (P = 1.6 × 10-8), and NID2-PTGDR (P = 4.2 × 10-8), and one novel locus associated with TG near WDR11-FGFR2 (P = 2.7 × 10-10). Conditional analyses identified a second signal near CD163-APOBEC1. We then combined results from the East Asian meta-analysis with association results from up to 187,365 European individuals from the Global Lipids Genetics Consortium in a trans-ancestry meta-analysis. This analysis identified (log10Bayes Factor ≥6.1) eight additional novel lipid loci. Among the twelve total loci identified, the index variants at eight loci have demonstrated at least nominal significance with other metabolic traits in prior studies, and two loci exhibited coincident eQTLs (P < 1 × 10-5) in subcutaneous adipose tissue for BPTF and PDGFC. Taken together, these analyses identified multiple novel lipid loci, providing new potential therapeutic targets
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