91 research outputs found
How Colors Influence Numbers: Photon Statistics of Parametric Downconversion
Parametric downconversion (PDC) is a technique of ubiquitous experimental
significance in the production of non-classical, photon-number correlated twin
beams. Standard theory of PDC as a two-mode squeezing process predicts and
homodyne measurements observe a thermal photon number distribution per beam.
Recent experiments have obtained conflicting distributions. In this paper, we
explain the observation by an a-priori theoretical model solely based on
directly accessible physical quantities. We compare our predictions with
experimental data and find excellent agreement.Comment: 4 {pages, figures
A proposed testbed for detector tomography
Measurement is the only part of a general quantum system that has yet to be
characterized experimentally in a complete manner. Detector tomography provides
a procedure for doing just this; an arbitrary measurement device can be fully
characterized, and thus calibrated, in a systematic way without access to its
components or its design. The result is a reconstructed POVM containing the
measurement operators associated with each measurement outcome. We consider two
detectors, a single-photon detector and a photon-number counter, and propose an
easily realized experimental apparatus to perform detector tomography on them.
We also present a method of visualizing the resulting measurement operators.Comment: 9 pages, 4 figure
Characterization of Spectral Entanglement of Spontaneous Parametric-Down Conversion Biphotons
We verified operational approach based on direct measurement of entanglement
degree for bipartite systems. In particular spectral distributions of single
counts and coincidence for pure biphoton states generated by train of short
pump pulses have been measured and entanglement quantifier calculated. The
approach gives upper bound of entanglement stored in total biphoton states,
which can reach extremely high value up to
Photon Number Statistics of Multimode Parametric Down-Conversion
We experimentally analyze the complete photon number statistics of parametric
downconversion and ascertain the influence of multimode effects. Our results
clearly reveal a difference between single mode theoretical description and the
measured distributions. Further investigations assure the applicability of
loss-tolerant photon number reconstruction and prove strict photon number
correlation between signal and idler modes.Comment: 5 pages, 3 figure
Fast quantum key distribution with decoy number states
We investigate the use of photon number states to identify eavesdropping
attacks on quantum key distribution (QKD) schemes. The technique is based on
the fact that different photon numbers traverse a channel with different
transmittivity. We then describe two QKD schemes that utilize this method, one
of which overcomes the upper limit on the key generation rate imposed by the
dead time of detectors when using a heralded source of photons.Comment: 15 pages, 6 figures; Accepted to J. Mod. Op
Spectral structure and decompositions of optical states, and their applications
We discuss the spectral structure and decomposition of multi-photon states.
Ordinarily `multi-photon states' and `Fock states' are regarded as synonymous.
However, when the spectral degrees of freedom are included this is not the
case, and the class of `multi-photon' states is much broader than the class of
`Fock' states. We discuss the criteria for a state to be considered a Fock
state. We then address the decomposition of general multi-photon states into
bases of orthogonal eigenmodes, building on existing multi-mode theory, and
introduce an occupation number representation that provides an elegant
description of such states that in many situations simplifies calculations.
Finally we apply this technique to several example situations, which are highly
relevant for state of the art experiments. These include Hong-Ou-Mandel
interference, spectral filtering, finite bandwidth photo-detection, homodyne
detection and the conditional preparation of Schr\"odinger Kitten and Fock
states. Our techniques allow for very simple descriptions of each of these
examples.Comment: 12 page
Optimised generation of heralded Fock states using parametric down conversion
The generation of heralded pure Fock states via spontaneous parametric down
conversion (PDC) relies on perfect photon-number correlations in the output
modes. Correlations in any other degree of freedom, however, degrade the purity
of the heralded state. In this paper, we investigate spectral entanglement
between the two output modes of a periodically poled waveguide. With the intent
of generating heralded 1- and 2-photon Fock states, we expand the output state
of the PDC to second order in photon number. We explore the effects of spectral
filtering and inefficient detection, of the heralding mode, on the count rate,
g(2) and purity of the heralded state, as well as the fidelity between the
resulting state and an ideal Fock state. We find that filtering can decrease
spectral correlations, however, at the expense of the count rate and increased
photon-number mixedness in the heralded output state. As a physical example, we
model a type II PP-KTP waveguide pumped by lasers at wavelengths of 400 nm, 788
nm and 1930 nm. The latter two allow the fulfillment of extended phase matching
conditions in an attempt to eliminate spectral correlations in the PDC output
state without the use of filtering, however, we find that even in these cases,
some filtering is needed to achieve states of very high purity.Comment: 28 pages, 25 figures, revised expressions for two-photon fidelit
Type 2 Diabetes Is Associated with Reduced ATP-Binding Cassette Transporter A1 Gene Expression, Protein and Function
Objective
Increasing plasma glucose levels are associated with increasing risk of vascular disease. We tested the hypothesis that there is a glycaemia-mediated impairment of reverse cholesterol transport (RCT). We studied the influence of plasma glucose on expression and function of a key mediator in RCT, the ATP binding cassette transporter-A1 (ABCA1) and expression of its regulators, liver X receptor-α (LXRα) and peroxisome proliferator-activated receptor–γ (PPARγ).
Methods and Results
Leukocyte ABCA1, LXRα and PPARγ expression was measured by polymerase chain reaction in 63 men with varying degrees of glucose homeostasis. ABCA1 protein concentrations were measured in leukocytes. In a sub-group of 25 men, ABCA1 function was quantified as apolipoprotein-A1-mediated cholesterol efflux from 2–3 week cultured skin fibroblasts. Leukocyte ABCA1 expression correlated negatively with circulating HbA1c and glucose (rho = −0.41, p<0.001; rho = −0.34, p = 0.006 respectively) and was reduced in Type 2 diabetes (T2DM) (p = 0.03). Leukocyte ABCA1 protein was lower in T2DM (p = 0.03) and positively associated with plasma HDL cholesterol (HDL-C) (rho = 0.34, p = 0.02). Apolipoprotein-A1-mediated cholesterol efflux correlated negatively with fasting glucose (rho = −0.50, p = 0.01) and positively with HDL-C (rho = 0.41, p = 0.02). It was reduced in T2DM compared with controls (p = 0.04). These relationships were independent of LXRα and PPARγ expression.
Conclusions
ABCA1 expression and protein concentrations in leukocytes, as well as function in cultured skin fibroblasts, are reduced in T2DM. ABCA1 protein concentration and function are associated with HDL-C levels. These findings indicate a glycaemia- related, persistent disruption of a key component of RCT
Renal cell carcinoma induces interleukin 10 and prostaglandin E2 production by monocytes
Immunotherapy with interleukin 2 (IL-2) is not an effective anti-cancer treatment in the majority of patients with renal cell carcinoma (RCC), suggesting that the activation of cytotoxic T cells or NK cells may be impaired in vivo in these patients. The production of immunosuppressive factors by RCC was investigated. Using immunohistochemistry, IL-10 was detectable in 10 of 21 tumour samples tested. IL-10 was undetectable in the supernatant of cell lines derived from these RCCs. However, these cell lines or their conditioned medium (RCC CM), but not normal renal epithelial cells adjacent to the RCC or breastcarcinoma cell lines, were found to induce IL-10, as well as prostaglandin E2 (PGE2) and tumour necrosis factor (TNF)α production by autologous or allogeneic peripheral blood mononuclear cells (PBMCs) and monocytes. IL-10 production induced by RCC CM was found to be dependent on TNF-α and PGE2 since an anti-TNF-α antibody (Ab) inhibited 40–70% of IL-10 production by monocytes, and the combination of anti-TNF-α Ab and indomethacin, an inhibitor of PGE2 production, inhibited 80–94% of RCC CM-induced IL-10 production by monocytes. The RCC CM of the five cell lines tested were found to induce a down-regulation of the expression of HLA-DR and CD86, as well as a strong inhibition of mannose receptor-dependent endocytosis by monocytes. The blockade of HLA-DR and CD86 expression was partially abrogated by indomethacin and anti-IL-10 Ab respectively, and completely abrogated by an anti-TNF-α Ab. The inhibition of mannose receptor-dependent endocytosis was partially abrogated by an anti-IL-10 Ab and completely abrogated by an anti-TNF-α Ab. These esults indicate that RCCs induce IL-10, PGE2 and TNF-α production by monocytes, which down-regulate the expression of cell-surface molecules involved in antigen presentation as well as their endocytic capacity. © 1999 Cancer Research Campaig
- …