596 research outputs found
Mode-selective quantization and multimodal effective models for spherically layered systems
We propose a geometry-specific, mode-selective quantization scheme in coupled
field-emitter systems which makes it easy to include material and geometrical
properties, intrinsic losses as well as the positions of an arbitrary number of
quantum emitters. The method is presented through the example of a spherically
symmetric, non-magnetic, arbitrarily layered system. We follow it up by a
framework to project the system on simpler, effective cavity QED models.
Maintaining a well-defined connection to the original quantization, we derive
the emerging effective quantities from the full, mode-selective model in a
mathematically consistent way. We discuss the uses and limitations of these
effective models
Transmon in a semi-infinite high-impedance transmission line: Appearance of cavity modes and Rabi oscillations
In this paper, we investigate the dynamics of a single superconducting artificial atom capacitively coupled to a transmission line with a characteristic impedance comparable to or larger than the quantum resistance. In this regime, microwaves are reflected from the atom also at frequencies far from the atom\u27s transition frequency. Adding a single mirror in the transmission line then creates cavity modes between the atom and the mirror. Investigating the spontaneous emission from the atom, we then find Rabi oscillations, where the energy oscillates between the atom and one of the cavity modes
Quantum Plasmonics with multi-emitters: Application to adiabatic control
We construct mode-selective effective models describing the interaction of N
quantum emitters (QEs) with the localised surface plasmon polaritons (LSPs)
supported by a spherical metal nanoparticle (MNP) in an arbitrary geometric
arrangement of the QEs. We develop a general formulation in which the field
response in the presence of the nanosystem can be decomposed into orthogonal
modes with the spherical symmetry as an example. We apply the model in the
context of quantum information, investigating on the possibility of using the
LSPs as mediators of an efficient control of population transfer between two
QEs. We show that a Stimulated Raman Adiabatic Passage configuration allows
such a transfer via a decoherence-free dark state when the QEs are located on
the same side of the MNP and very closed to it, whereas the transfer is blocked
when the emitters are positioned at the opposite sides of the MNP. We explain
this blockade by the destructive superposition of all the interacting plasmonic
modes
Production of photon states from Λ-atoms in a cavity
We analyse the system of Λ-atoms in a cavity QED of semi-transparent mirror and driven by laser fields. We derive effective models and connect concepts (photonic flux, input-output operators, photonic state) characterizing the propagation of the resulting leaking photons. We propose an atom-cavity non-resonant scheme for single-and 2-photons generation. The pulse shapes of outgoing single photons are tailored using a specifically designed driving field envelope. For the production of 2-photon states, two trapped atoms are used with two driving pulses. Their pulse shapes are characterized and it is shown that the multiphoton outgoing photonic states cannot be Fock states, since the photons are not generated strictly simultaneously
Horizon effects with surface waves on moving water
Surface waves on a stationary flow of water are considered, in a linear model
that includes the surface tension of the fluid. The resulting gravity-capillary
waves experience a rich array of horizon effects when propagating against the
flow. In some cases three horizons (points where the group velocity of the wave
reverses) exist for waves with a single laboratory frequency. Some of these
effects are familiar in fluid mechanics under the name of wave blocking, but
other aspects, in particular waves with negative co-moving frequency and the
Hawking effect, were overlooked until surface waves were investigated as
examples of analogue gravity [Sch\"utzhold R and Unruh W G 2002 Phys. Rev. D 66
044019]. A comprehensive presentation of the various horizon effects for
gravity-capillary waves is given, with emphasis on the deep water/short
wavelength case kh>>1 where many analytical results can be derived. A
similarity of the state space of the waves to that of a thermodynamic system is
pointed out.Comment: 30 pages, 15 figures. Minor change
Hawking Radiation on an Ion Ring in the Quantum Regime
This paper discusses a recent proposal for the simulation of acoustic black
holes with ions. The ions are rotating on a ring with an inhomogeneous, but
stationary velocity profile. Phonons cannot leave a region, in which the ion
velocity exceeds the group velocity of the phonons, as light cannot escape from
a black hole. The system is described by a discrete field theory with a
nonlinear dispersion relation. Hawking radiation is emitted by this acoustic
black hole, generating entanglement between the inside and the outside of the
black hole. We study schemes to detect the Hawking effect in this setup.Comment: 42 pages (one column), 17 figures, published revised versio
Physical activity and sedentary behavior from 6 to 11 years
OBJECTIVES: Physical activity (PA) is presumed to decline during childhood and adolescence, but only few long-term studies about PA development during this period of life exist. We assessed PA and sedentary behavior (SB) over a 5-year period to gain a better understanding of the extent of change in activity and potential influencing factors. METHODS: PA and SB of 600 children from the Childhood Obesity Project were objectively measured with the SenseWear Armband 2 at the ages of 6, 8, and 11 years, resulting in 1254 observations. Longitudinal changes of total PA, moderate-to-vigorous physical activity (MVPA), light physical activity (LPA), and SB were modeled with mixed-effects models. RESULTS: Total PA revealed a significant quadratic decline with age (P < .001), resulting in a change of total PA by -75.3 minutes per day from 6 to 11 years. LPA linearly declined (P < .001) by 44.6 minutes per day, MVPA quadratically declined (P < .001) by an overall 30.7 minutes, whereas SB increased significantly (+107 minutes; P = .001). Boys showed a steeper decline in LPA (P = .003) and MVPA (P < .001) than did girls. Higher fat mass index and BMI z scores were associated with lower levels of total PA and MVPA and higher levels of SB (all P < .001). CONCLUSIONS: We showed that PA decreased, and SB increased in earlier years than previously thought. MVPA remained relatively stable until 8 years, but revealed a drop-off at 11 years, identifying this period as a crucial time for intervention
On the robustness of entanglement in analogue gravity systems
We investigate the possibility of generating quantum-correlated quasi-particles utilizing analogue gravity systems. The quantumness of these correlations is a key aspect of analogue gravity effects and their presence allows for a clear separation between classical and quantum analogue gravity effects. However, experiments in analogue systems, such as Bose–Einstein condensates (BECs) and shallow water waves, are always conducted at non-ideal conditions, in particular, one is dealing with dispersive media at non-zero temperatures. We analyse the influence of the initial temperature on the entanglement generation in analogue gravity phenomena. We lay out all the necessary steps to calculate the entanglement generated between quasi-particle modes and we analytically derive an upper bound on the maximal temperature at which given modes can still be entangled. We further investigate a mechanism to enhance the quantum correlations. As a particular example, we analyse the robustness of the entanglement creation against thermal noise in a sudden quench of an ideally homogeneous BEC, taking into account the super-sonic dispersion relations
Modeling atmospheric effects of the September 1859 Solar Flare
We have modeled atmospheric effects, especially ozone depletion, due to a
solar proton event which probably accompanied the extreme magnetic storm of 1-2
September 1859. We use an inferred proton fluence for this event as estimated
from nitrate levels in Greenland ice cores. We present results showing
production of odd nitrogen compounds and their impact on ozone. We also compute
rainout of nitrate in our model and compare to values from ice core data.Comment: Revised version including improved figures; Accepted for publication
in Geophys. Res. Lett, chosen to be highlighted by AG
Earthworm management in tropical agroecosystems
Collaborative research in the Macrofauna project has enabled development of some techniques that presently are at different stages of advancement, from promising pilot experiments (tomato production and inoculation in plant nursery bags at Yurimaguas and in India) to the fully developed technique of massive worm production and biofertilization of tea gardens in Tamil Nadu (India) (patent deposited). Failures have also helped to gain better insight into the potential feasibility of techniques that had been considered in the objectives of this project. Endogeic earthworms (#Pontoscolex corethrurus$) may be produced in large quantities, i.e.about 12000 worms (1.6-2.8 kg live wt)/m2/year in specific culture beds using either sawdust (Yurimaguas, Peru) or a mixture of high and low quality materials (Tamil Nadu, India) mixed into soil as substrates. Cost of production of 1 kg of earthworm biomass through bed culture is about 3.6 Euro, much lower than the cost of hand collection of worms from pastures/grasslands where these species are abundant (6-125 Euro depending on the cost of labour and earthworm density). The theorical value of an active earthworm community with an average biomass of 400 kg live wt has been estimated at 1400 Euro, the price that it would cost to reintroduce an equivalent biomass produced in our culture units, indicating the cost of land restoration. Direct inoculation of earthworms in the field to improve production may only affect plant growth positively if a large biomass (greater than 30 g live wt/m2) is inoculated from the beginning. An alternative may be to concentrate the inoculum in small areas regularly distributed across the field... (D'après résumé d'auteur
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