2,109 research outputs found
Competing many-body interactions in systems of trapped ions
We propose and theoretically analyse an experimental configuration in which
lasers induce 3-spin interactions between trapped ions.By properly choosing the
intensities and frequencies of the lasers, 3-spin couplings may be dominant or
comparable to 2-spin terms and magnetic fields. In this way, trapped ions can
be used to study exotic quantum phases which do not have a counterpart in
nature. We study the conditions for the validity of the effective 3-spin
Hamiltonian, and predict qualitatively the quantum phase diagram of the system.Comment: RevTex4 file, color figure
Zeno dynamics in wave-packet diffraction spreading
We analyze a simple and feasible practical scheme displaying Zeno, anti-Zeno,
and inverse-Zeno effects in the observation of wave-packet spreading caused by
free evolution. The scheme is valid both in spatial diffraction of classical
optical waves and in time diffraction of a quantum wave packet. In the optical
realization, diffraction spreading is observed by placing slits between a light
source and a light-power detector. We show that the occurrence of Zeno or
anti-Zeno effects depends just on the frequency of observations between the
source and detector. These effects are seen to be related to the diffraction
mode theory in Fabry-Perot resonators.Comment: 7 pages, 8 figure
The three-dimensional carrier-envelope-phase map of focused few-cycle pulsed Gaussian beams
We derive an analytical expression that describes the complete
three-dimensional carrier-envelope phase (CEP) distribution of in the focal
volume of ultrashort pulsed Gaussian beams focused by spherical mirrors or
lenses. The focal CEP map depends on the so-called factor specifying the
frequency-dependence of the beam width of the source few-cycle pulse, on its
chirp and on the small chromatic aberration introduced by a lens without
appreciably distorting or broadening the few-cycle pulse. We show how to tailor
the CEP map of mirror-focused and lens-focused few-cycle pulses in order to
produce negligible transversal and axial CEP variations in specific regions of
the focal volume for phase-sensitive interactions of light with matter taking
place in a volume or on a surface. We propose a quasi-achromatic doublet lens
that can implement in practice these tailored CEP distributions.Comment: 9 pages, 6 figure
OH+ in Diffuse Molecular Clouds
Near ultraviolet observations of OH+ and OH in diffuse molecular clouds
reveal a preference for different environments. The dominant absorption feature
in OH+ arises from a main component seen in CH+ (that with the highest CH+/CH
column density ratio), while OH follows CN absorption. This distinction
provides new constraints on OH chemistry in these clouds. Since CH+ detections
favor low-density gas with small fractions of molecular hydrogen, this must be
true for OH+ as well, confirming OH+ and H2O+ observations with the Herschel
Space Telescope. Our observed correspondence indicates that the cosmic ray
ionization rate derived from these measurements pertains to mainly atomic gas.
The association of OH absorption with gas rich in CN is attributed to the need
for high enough density and molecular fraction before detectable amounts are
seen. Thus, while OH+ leads to OH production, chemical arguments suggest that
their abundances are controlled by different sets of conditions and that they
coexist with different sets of observed species. Of particular note is that
non-thermal chemistry appears to play a limited role in the synthesis of OH in
diffuse molecular clouds.Comment: 15 pages, 4 figures, to appear in ApJ Letter
Mesoscopic mean-field theory for spin-boson chains in quantum optical systems
We present a theoretical description of a system of many spins strongly coupled to a bosonic chain. We rely on the use of a spin-wave theory describing the Gaussian fluctuations around the mean-field solution, and focus on spin-boson chains arising as a generalization of the Dicke Hamiltonian. Our model is motivated by experimental setups such as trapped ions, or atoms/qubits coupled to cavity arrays. This situation corresponds to the cooperative (E⊗β) Jahn-Teller distortion studied in solid-state physics. However, the ability to tune the parameters of the model in quantum optical setups opens up a variety of novel intriguing situations. The main focus of this paper is to review the spin-wave theoretical description of this problem as well as to test the validity of mean-field theory. Our main result is that deviations from mean-field effects are determined by the interplay between magnetic order and mesoscopic cooperativity effects, being the latter strongly size-dependent
Microwave energy supplied by a prototype oven prevents the spread of Fusarium wilt during the propagation of melon plantlets by seed
The re-use of propagation trays in nursery greenhouses is one of the main ways in which fusarium wilt is spread in melon crops (Cucumis melo). The causal agent of the disease is the fungus Fusarium oxysporum f. sp. melonis. This paper reports that exposing these seed trays to the energy produced by a prototype microwave oven during the commercial production of melon plantlets can prevent the spread of this pathogen with only a very small increase in production costs
Coherent Modulation of the YBa2Cu3O6+x Atomic Structure by Displacive Stimulated Ionic Raman Scattering
We discuss the mechanism of coherent phonon generation by Stimulated Ionic
Raman Scattering, a process different from conventional excitation with near
visible optical pulses. Ionic Raman scattering is driven by anharmonic coupling
between a directly excited infrared-active phonon mode and other Raman modes.
We experimentally study the response of YBa2Cu3O6+x to the resonant excitation
of apical oxygen motions at 20 THz by mid-infrared pulses, which has been shown
in the past to enhance the interlayer superconducting coupling. We find
coherent oscillations of four totally symmetric (Ag) Raman modes and make a
critical assessment of the role of these oscillatory motions in the enhancement
of superconductivity.Comment: 12 pages, 4 figure
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