45 research outputs found
Disruption of reflecting Bose-Einstein condensates due to inter-atomic interactions and quantum noise
We perform fully three-dimensional simulations, using the truncated Wigner
method, to investigate the reflection of Bose-Einstein condensates from abrupt
potential barriers. We show that the inter-atomic interactions can disrupt the
internal structure of a cigar-shaped cloud with a high atom density at low
approach velocities, damping the center-of-mass motion and generating vortices.
Furthermore, by incorporating quantum noise we show that scattering halos form
at high approach velocities, causing an associated condensate depletion. We
compare our results to recent experimental observations.Comment: 5 figure
Integrated tunneling sensor for nanoelectromechanical systems
Transducers based on quantum mechanical tunneling provide an extremely sensitive sensor principle, especially for nanoelectromechanical systems. For proper operation a gap between the electrodes of below 1nm is essential, requiring the use of structures with a mobile electrode. At such small distances, attractive van der Waals and capillary forces become sizable, possibly resulting in snap-in of the electrodes. The authors present a comprehensive analysis and evaluation of the interplay between the involved forces and identify requirements for the design of tunnelingsensors. Based on this analysis, a tunnelingsensor is fabricated by Si micromachiningtechnology and its proper operation is demonstrated
Magnetic interactions of cold atoms with anisotropic conductors
We analyze atom-surface magnetic interactions on atom chips where the
magnetic trapping potentials are produced by current carrying wires made of
electrically anisotropic materials. We discuss a theory for time dependent
fluctuations of the magnetic potential, arising from thermal noise originating
from the surface. It is shown that using materials with a large electrical
anisotropy results in a considerable reduction of heating and decoherence rates
of ultra-cold atoms trapped near the surface, of up to several orders of
magnitude. The trap loss rate due to spin flips is expected to be significantly
reduced upon cooling the surface to low temperatures. In addition, the
electrical anisotropy significantly suppresses the amplitude of static spatial
potential corrugations due to current scattering within imperfect wires. Also
the shape of the corrugation pattern depends on the electrical anisotropy: the
preferred angle of the scattered current wave fronts can be varied over a wide
range. Materials, fabrication, and experimental issues are discussed, and
specific candidate materials are suggested.Comment: Selected as a Highlight paper in the European Physical Journal
Teleportation of a quantum state of a spatial mode with a single massive particle
Mode entanglement exists naturally between regions of space in ultra-cold
atomic gases. It has, however, been debated whether this type of entanglement
is useful for quantum protocols. This is due to a particle number
superselection rule that restricts the operations that can be performed on the
modes. In this paper, we show how to exploit the mode entanglement of just a
single particle for the teleportation of an unknown quantum state of a spatial
mode. We detail how to overcome the superselection rule to create any initial
quantum state and how to perform Bell state analysis on two of the modes. We
show that two of the four Bell states can always be reliably distinguished,
while the other two have to be grouped together due to an unsatisfied phase
matching condition. The teleportation of an unknown state of a quantum mode
thus only succeeds half of the time.Comment: 12 pages, 1 figure, this paper was presented at TQC 2010 and extends
the work of Phys. Rev. Lett. 103, 200502 (2009
Measurement of the CP-violating phase phi_s in the decay Bs->J/psi phi
We present a measurement of the time-dependent CP-violating asymmetry in B_s
-> J/psi phi decays, using data collected with the LHCb detector at the LHC.
The decay time distribution of B_s -> J/psi phi is characterized by the decay
widths Gamma_H and Gamma_L of the heavy and light mass eigenstates of the
B_s-B_s-bar system and by a CP-violating phase phi_s. In a sample of about 8500
B_s -> J/psi phi events isolated from 0.37 fb^-1 of pp collisions at sqrt(s)=7
TeV we measure phi_s = 0.15 +/- 0.18 (stat) +/- 0.06 (syst) rad. We also find
an average B_s decay width Gamma_s == (Gamma_L + Gamma_H)/2 = 0.657 +/- 0.009
(stat) +/- 0.008 (syst) ps^-1 and a decay width difference Delta Gamma_s ==
Gamma_L - Gamma_H} = 0.123 +/- 0.029 (stat) +/- 0.011 (syst) ps^-1. Our
measurement is insensitive to the transformation (phi_s,DeltaGamma_s --> pi -
phi_s, - Delta Gamma_s.Comment: 9 pages, 3 figure
Effect of hygroscopic growth on the aerosol light-scattering coefficient: A review of measurements, techniques and error sources
Knowledge of the scattering enhancement factor, f(RH), is important for an accurate description of direct
aerosol radiative forcing. This factor is defined as the ratio between the scattering coefficient at enhanced
relative humidity, RH, to a reference (dry) scattering coefficient. Here, we review the different experimental
designs used to measure the scattering coefficient at dry and humidified conditions as well as the
procedures followed to analyze the measurements. Several empirical parameterizations for the relationship
between f(RH) and RH have been proposed in the literature. These parameterizations have been
reviewed and tested using experimental data representative of different hygroscopic growth behavior
and a new parameterization is presented. The potential sources of error in f(RH) are discussed. A Monte
Carlo method is used to investigate the overall measurement uncertainty, which is found to be around 20
e40% for moderately hygroscopic aerosols. The main factors contributing to this uncertainty are the
uncertainty in RH measurement, the dry reference state and the nephelometer uncertainty. A literature
survey of nephelometry-based f(RH) measurements is presented as a function of aerosol type. In general,
the highest f(RH) values were measured in clean marine environments, with pollution having a major
influence on f(RH). Dust aerosol tended to have the lowest reported hygroscopicity of any of the aerosol
types studied. Major open questions and suggestions for future research priorities are outlined.This work was supported by the Andalusia Regional Government through projects P10-RNM-6299 and P12-RNM-2409; by the Spanish Ministry of Economy and Competitiveness and FEDER through project CGL2013_45410-R; and by European Unionâs Horizon 2020 research and innovation programme under grant agreement No 654109, ACTRIS-2. G. Titos was partially funded by Programa del Plan Propio de InvestigaciĂłn âContrato Puenteâ of the University of Granada. We thank the Stockholm International Meteorological Institute (IMI) for travel support of G. Titos
Study of the relative humidity dependence of aerosol light-scattering in southern Spain
This investigation focuses on the characterisation of the aerosol particle hygroscopicity. Aerosol particle optical
properties were measured at Granada, Spain, during winter and spring seasons in 2013. Measured optical
properties included particle light-absorption coefficient (sap) and particle light-scattering coefficient (ssp) at dry
conditions and at relative humidity (RH) of 85 +/- 10%. The scattering enhancement factor, f(RH=85%), had a
mean value of 1.5 +/- 0.2 and 1.6 +/- 0.3 for winter and spring campaigns, respectively. Cases of high scattering
enhancement were more frequent during the spring campaign with 27% of the f(RH=85%) values above
1.8, while during the winter campaign only 8% of the data were above 1.8. A Saharan dust event (SDE), which
occurred during the spring campaign, was characterised by a predominance of large particles with low
hygroscopicity. For the day when the SDE was more intense, a mean daily value of f(RH=85%)=1.3 +/- 0.2 was
calculated. f(RH=85%) diurnal cycle showed two minima during the morning and afternoon traffic rush hours
due to the increase in non-hygroscopic particles such as black carbon and road dust. This was confirmed by
small values of the single-scattering albedo and the scattering Angstrom exponent. A significant correlation
between f(RH=85%) and the fraction of particulate organic matter and sulphate was obtained. Finally, the
impact of ambient RH in the aerosol radiative forcing was found to be very small due to the low ambient RH.
For high RH values, the hygroscopic effect should be taken into account since the aerosol forcing efficiency
changed from -13W/m2 at dry conditions to -17W/m2 at RH=85%.This work was supported by the Andalusia Regional Government through projects P10-RNM-6299 and P12-RNM-2409; by the Spanish Ministry of Economy and Competitiveness through projects CGL2010-18782, CSD2007-00067, CGL2011-13580-E/CLI and CGL2011-16124-E; and by EU through ACTRIS project (EU INFRA-2010-1.1.16-262254).G. Titos was funded by the program FPI of the Spanish Ministry of Economy and Competitiveness â Secretariat of Science, Innovation and Development under grant BES-2011-043721
Search for the lepton number violating decays and
A search is performed for the lepton number violating decay , where represents a or a , using data from the
LHCb detector corresponding to an integrated luminosity of . The
decay is forbidden in the Standard Model but allowed in models with a Majorana
neutrino. No signal is observed in either channel and limits of and are set at the 95% confidence level. These improve the
previous best limits by factors of 40 and 30, respectively
Measurement of the cross-section ratio for prompt production at TeV
The prompt production of the charmonium and mesons
has been studied in proton-proton collisions at the Large Hadron Collider at a
centre-of-mass energy of TeV. The mesons are identified
through their decays with
using 36 of data collected by the LHCb detector in 2010. The
ratio of the prompt production cross-sections for the two spin states,
, has been determined as a function of the
transverse momentum, , in the range from 2 to
15 GeV/. The results are in agreement with the next-to-leading order
non-relativistic QCD model at high and lie
consistently above the pure leading-order colour singlet prediction.Comment: 13 pages, 3 figure
Measurement of b hadron production fractions in 7 TeV pp collisions
Measurements of hadron production ratios in proton-proton collisions at a
centre-of-mass energy of 7 TeV with an integrated luminosity of 3 pb are
presented. We study the ratios of strange meson to light meson
production and baryon to light meson
production as a function of the charmed hadron-muon
pair transverse momentum and the hadron pseudorapidity , for
between 0 and 14 GeV and between 2 and 5. We find that
is consistent with being independent of and ,
and we determine = 0.134 0.004 , where
the first error is statistical and the second systematic. The corresponding
ratio is found to be dependent upon the transverse
momentum of the charmed hadron-muon pair, , where Br reflects an absolute scale
uncertainty due to the poorly known branching fraction Br(\Lambda_c^+ \to
pK^-\pi^+)BBf_s/f_d\bar{B}_s \to
D_S^+ \pi ^-\bar{B}^0 \to D^+K^-\bar{B}^0 \to D^+\pi^-f_s/f_d=0.267^{+0.021}_{-0.020}$.Comment: 28 pages, 12 figures, version accepted for publication in Physical
Review D, few more detailed explanations on analysis methods adde