5,415 research outputs found
Entangled light pulses from single cold atoms
The coherent interaction between a laser-driven single trapped atom and an
optical high-finesse resonator allows to produce entangled multi-photon light
pulses on demand. The mechanism is based on the mechanical effect of light. The
degree of entanglement can be controlled through the parameters of the laser
excitation. Experimental realization of the scheme is within reach of current
technology. A variation of the technique allows for controlled generation of
entangled subsequent pulses, with the atomic motion serving as intermediate
memory of the quantum state.Comment: 4 pages, 3 figures, revised version (new scheme for generation of
subsequent pairs of entangled pulses included). Accepted for publication in
Phys. Rev. Let
Inelastic scattering of light by a cold trapped atom: Effects of the quantum center-of-mass motion
The light scattered by a cold trapped ion, which is in the stationary state
of laser cooling, presents features due to the mechanical effects of
atom-photon interaction. These features appear as additional peaks (sidebands)
in the spectrum of resonance fluorescence. Among these sidebands the literature
has discussed the Stokes and anti-Stokes components, namely the sidebands of
the elastic peak. In this manuscript we show that the motion also gives rise to
sidebands of the inelastic peaks. These are not always visible, but, as we
show, can be measured in parameter regimes which are experimentally accessible.Comment: 10 pages, 4 figures, submitted to Phys. Rev.
Erratum to: Sexual Mixing in Shanghai: Are Heterosexual Contact Patterns Compatible With an HIV/AIDS Epidemic?
In the middle of the paragraph just above Figure 6, there is the following sentence: âThe range of the mean of the distribution of the proportion infected generated by the simulations is narrow, between 0.5 % and 0.2 % of all nodes.â This should read âbetween 0.05 % and 0.2 % of all nodes.
Thermal and quantum fluctuations in chains of ultracold polar molecules
Ultracold polar molecules, in highly anisotropic traps and interacting via a
repulsive dipolar potential, may form one-dimensional chains at high densities.
According to classical theory, at low temperatures there exists a critical
value of the density at which a second order phase transition from a linear to
a zigzag chain occurs. We study the effect of thermal and quantum fluctuations
on these self-organized structures using classical and quantum Monte Carlo
methods, by means of which we evaluate the pair correlation function and the
static structure factor. Depending on the parameters, these functions exhibit
properties typical of a crystalline or of a liquid system. We compare the
thermal and the quantum results, identifying analogies and differences.
Finally, we discuss experimental parameter regimes where the effects of quantum
fluctuations on the linear - zigzag transition can be observed.Comment: Submitted to the Special issue on modern applications of trapped
ions, J. Phys. B: At. Mol. Opt. Phy
Influence of hepatitis delta virus infection on morbidity and mortality in compensated cirrhosis type B
BACKGROUNDâThe effect of hepatitis delta virus (HDV) infection on the clinical course of cirrhosis type B is poorly defined.âšAIMSâTo investigate the impact of HDV status on morbidity and mortality in cirrhosis type B.âšPATIENTS/METHODSâRetrospective cohort study of 200 Western European patients with compensated cirrhosis type B followed for a median period of 6.6( )years.âšRESULTSâAt diagnosis, 20% of patients had antibodies to HDV (anti-HDV); median age was lower in anti-HDV positive cirrhotics (34 v 48 years respectively). Kaplan-Meier five year probability of hepatocellular carcinoma (HCC) was 6, 10, and 9% in anti-HDV positive/HBeAg negative, anti-HDV negative/HBeAg negative, and anti-HDV negative/HBeAg positive cirrhotics respectively; the corresponding figures for decompensation were 22, 16, and 19% and for survival they were 92, 89, and 83% respectively. Cox regression analysis identified age, albumin concentration, Îł-globulin concentration, and HDV status as significant independent prognostic variables. After adjustment for clinical and serological differences at baseline, the risk (95% confidence interval) for HCC, decompensation, and mortality was increased by a factor of 3.2 (1.0 to 10), 2.2 (0.8( )to 5.7), and 2.0 (0.7 to 5.7) respectively in anti-HDV positive relative to HDV negative cirrhotic patients. The adjusted estimated five year risk for HCC was 13, 4, and 2% for anti-HDV positive/HBeAg negative, anti-HDV negative/HBeAg negative, and anti-HDV negative/HBeAg positive cirrhotics respectively; the corresponding figures for decompensation were 18, 8, and 14% and for survival 90, 95, and 93% respectively.âšCONCLUSIONSâHDV infection increases the risk for HCC threefold and for mortality twofold in patients with cirrhosis type B.âšâšâšKeywords: delta hepatitis; prognosis; hepatocellular carcinoma; decompensation; surviva
Cryogenic R&D at the CERN Central Cryogenic Laboratory
The Central Cryogenic Laboratory operates since many years at CERN in the framework of cryogenic R&D for accelerators and experiments. The laboratory hosts several experimental posts for small cryogen ic tests, all implemented with pumping facility for GHe and vacuum, and is equipped with a He liquefier producing 6.105 l/year, which is distributed in dewars. Tests include thermomechanical qualifica tion of structural materials, cryogenic and vacuum qualification of prototypes, evaluation of thermal losses of components. Some of the most relevant results obtained at the laboratory in the last yea rs are outlined in this paper
Unified Treatment of Heterodyne Detection: the Shapiro-Wagner and Caves Frameworks
A comparative study is performed on two heterodyne systems of photon
detectors expressed in terms of a signal annihilation operator and an image
band creation operator called Shapiro-Wagner and Caves' frame, respectively.
This approach is based on the introduction of a convenient operator
which allows a unified formulation of both cases. For the Shapiro-Wagner
scheme, where , quantum phase and amplitude
are exactly defined in the context of relative number state (RNS)
representation, while a procedure is devised to handle suitably and in a
consistent way Caves' framework, characterized by , within the approximate simultaneous measurements of
noncommuting variables. In such a case RNS phase and amplitude make sense only
approximately.Comment: 25 pages. Just very minor editorial cosmetic change
Physical realization of a quantum spin liquid based on a novel frustration mechanism
Unlike conventional magnets where the magnetic moments are partially or
completely static in the ground state, in a quantum spin liquid they remain in
collective motion down to the lowest temperatures. The importance of this state
is that it is coherent and highly entangled without breaking local symmetries.
Such phenomena is usually sought in simple lattices where antiferromagnetic
interactions and/or anisotropies that favor specific alignments of the magnetic
moments are "frustrated" by lattice geometries incompatible with such order
e.g. triangular structures. Despite an extensive search among such compounds,
experimental realizations remain very few. Here we describe the investigation
of a novel, unexplored magnetic system consisting of strong ferromagnetic and
weaker antiferromagnetic isotropic interactions as realized by the compound
CaCrO. Despite its exotic structure we show both
experimentally and theoretically that it displays all the features expected of
a quantum spin liquid including coherent spin dynamics in the ground state and
the complete absence of static magnetism.Comment: Modified version accepted in Nature Physic
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