4,732 research outputs found
Real-Time Cavity QED with Single Atoms
The combination of cold atoms and large coherent coupling enables investigations in a new regime in cavity QED with single-atom trajectories monitored in real time with high signal-to-noise ratio. The underlying âvacuum-Rabiâ splitting is clearly reflected in the frequency dependence of atomic transit signals recorded atom by atom, with evidence for mechanical light forces for intracavity photon number <1. The nonlinear optical response of one atom in a cavity is observed to be in accord with the one-atom quantum theory but at variance with semiclassical predictions
Real-time cavity QED with single atoms
We report the first measurement of the real-time evolution of the complex field amplitude brought on by single atom transits. We show the variation in time of both quadrature amplitudes (simultaneously recorded) of the light transmitted through the cavity, as well the resultant optical phase for a single atom transit event. In this particular measurement, the cavity and laser were both detuned by 10 MHz from the Cs resonance
Assessment of the variability of airborne contamination levels in an intensive care unit over a 24 hour period
Introduction: The objective of this study was to evaluate the variability in the dynamics and levels of airborne contamination within a hospital ICU in order to establish an improved understanding of the extent to which airborne bioburden contributes to cross-infection of patients. Microorganisms from the respiratory tract or skin can become airborne by coughing, sneezing and periods of increased activity such as bed changes and staff rounds. Current knowledge of the clinical microflora is limited however it is estimated that 10-33% of nosocomial infections are transmitted via air. Methods: Environmental air monitoring was conducted in Glasgow Royal Infirmary ICU, in the open ward and in patient isolation rooms. A sieve impactor air sampler was used to collect 500 L air samples every 15 minutes over 10 hour (08:00-18:00 h) and 24 hour (08:00-08:00 h) periods. Samples were collected, room activity logged and the bacterial contamination levels were recorded as CFU/m3 of air. Results: A high degree of variability in levels of airborne contamination was observed over the course of a 10 hour day and a 24 period in a hospital ICU. Counts ranged from 12-510 CFU/m3 over 24 hours in an isolation room occupied for 10 days by a patient with C. difficile infection. Contamination levels were found to be lowest during the night and in unoccupied rooms, with an average value of 20 CFU/m3. Peaks in airborne contamination showed a direct relation to an increase in room activity. Conclusions: This study demonstrates the degree of airborne contamination that can occur in an ICU over a 24 hour period. Numerous factors were found to contribute to microbial air contamination and consideration should be given to potential improved infection control strategies and decontamination technologies which could be deployed within the clinical environment to reduce the airborne contamination levels, with the ultimate aim of reducing healthcare-associated infections from environmental sources
Polariton Analysis of a Four-Level Atom Strongly Coupled to a Cavity Mode
We present a complete analytical solution for a single four-level atom
strongly coupled to a cavity field mode and driven by external coherent laser
fields. The four-level atomic system consists of a three-level subsystem in an
EIT configuration, plus an additional atomic level; this system has been
predicted to exhibit a photon blockade effect. The solution is presented in
terms of polaritons. An effective Hamiltonian obtained by this procedure is
analyzed from the viewpoint of an effective two-level system, and the dynamic
Stark splitting of dressed states is discussed. The fluorescence spectrum of
light exiting the cavity mode is analyzed and relevant transitions identified.Comment: 12 pages, 9 figure
Petrogenesis of diachronous mixed siliciclastic-carbonate megafacies in the cool-water Oligocene Tikorangi Formation, Taranaki Basin, New Zealand
The Oligocene (Whaingaroan-Waitakian) Tikorangi Formation is a totally subsurface, lithostratigraphically complex, mixed siliciclastic-limestone-rich sequence forming an important fracture reservoir within Taranaki Basin, New Zealand. Petrographically the formation comprises a spectrum of interbedded rock types ranging from calcareous mudstone to wackestone to packstone to clean sparry grainstone. Skeletal and textural varieties within these rock types have aided in the identification of three environmentally distinctive megafacies for the Tikorangi Formation rocks-shelfal, foredeep, and basinal. Data from these megafacies have been used to detail previous conclusions on the petrogenesis and to further refine depositional paleoenvironmental models for the Tikorangi Formation in the central eastern Taranaki Basin margin.Shelfal Megafacies 1 rocks (reference well Hu Road-1A) are latest Oligocene (early Waitakian) in age and formed on or proximal to the Patea-Tongaporutu-Herangi basement high. They are characterised by coarse, skeletal-rich, pure sparry grainstone comprising shallow water, high energy taxa (bryozoans, barnacles, red algae) and admixtures of coarse well-rounded lithic sand derived from Mesozoic basement greywacke. This facies type has previously gone unrecorded in the Tikorangi Formation. Megafacies 2 is a latest Oligocene (early Waitakian) foredeep megafacies (formerly named shelfal facies) formed immediately basinward and west of the shelfal basement platform. It accumulated relatively rapidly (>20 cm/ka) from redeposition of shelfal megafacies biota that became intermixed with bathyal taxa to produce a spectrum of typically mudstone through to sparry grainstone. The resulting skeletal mix (bivalve, echinoderm, planktic and benthic foraminiferal, red algal, bryozoan, nannofossil) is unlike that in any of the age-equivalent limestone units in neighbouring onland King Country Basin. Megafacies 3 is an Oligocene (Whaingaroan-Waitakian) offshore basinal megafacies (formerly termed bathyal facies) of planktic foraminiferal-nannofossil-siliciclastic wackestone and mudstone formed away from redepositional influences. The siliciclastic input in this distal basinal setting (sedimentation rates <7 mm/ka) was probably sourced mainly from oceanic currents carrying suspended sediment from South Island provenances exposed at this time.Tikorangi Formation rocks record the Taranaki Basinâs only period of carbonate-dominated sedimentation across a full range of shelfal, foredeep, and basinal settings. Depositional controls on the three contrasting megafacies were fundamentally the interplay of an evolving and complex plate tectonic setting, including development of a carbonate foredeep, changes in relative sea level within an overall transgressive regime, and changing availability, sources, and modes of deposition of both bioclastic and siliciclastic sediments. The mixed siliciclastic-carbonate nature of the formation, and its skeletal assemblages, low-Mg calcite mineralogy, and delayed deep burial diagenetic history, are features consistent with formation in temperate-latitude cool waters
Trapping of Single Atoms with Single Photons in Cavity QED
Two recent experiments have reported the trapping of individual atoms inside
optical resonators by the mechanical forces associated with single photons
[Hood et al., Science 287, 1447 (2000) and Pinkse et al., Nature 404, 365
(2000)]. Here we analyze the trapping dynamics in these settings, focusing on
two points of interest. Firstly, we investigate the extent to which
light-induced forces in these experiments are distinct from their free-space
counterparts. Secondly, we explore the quantitative features of the resulting
atomic motion and how these dynamics are mapped onto variations of the
intracavity field. Not surprisingly, qualitatively distinct atomic dynamics
arise as the coupling and dissipative rates are varied. For the experiment of
Hood et al., we show that atomic motion is largely conservative and is
predominantly in radial orbits transverse to the cavity axis. A comparison with
the free-space theory demonstrates that the fluctuations of the dipole force
are suppressed by an order of magnitude. This effect is based upon the
Jaynes-Cummings eigenstates of the atom-cavity system and represents
qualitatively new physics for optical forces at the single-photon level. By
contrast, even in a regime of strong coupling in the experiment of Pinkse et
al., there are only small quantitative distinctions between the free-space
theory and the quantum theory, so it is not clear that description of this
experiment as a novel single-quantum trapping effect is necessary. The atomic
motion is strongly diffusive, leading to an average localization time
comparable to the time for an atom to transit freely through the cavity and to
a reduction in the ability to infer aspects of the atomic motion from the
intracavity photon number.Comment: 19 pages, 22 figure files, REVTEX, corrected spelling, LaTeX now
produces postscript which includes figures, minor changes to figures. Final
version to be published in Physical Review A, expanded summary of results in
introduction, minor changes to figures and tex
Resonator-Enhanced Optical Dipole Trap for Fermionic Lithium Atoms
We demonstrate a novel optical dipole trap which is based on the enhancement
of the optical power density of a Nd:YAG laser beam in a resonator. The trap is
particularly suited for experiments with ultracold gases, as it combines a
potential depth of order 1 mK with storage times of several tens of seconds. We
study the interactions in a gas of fermionic lithium atoms in our trap and
observe the influence of spin-changing collisions and off-resonant photon
scattering. A key element in reaching long storage times is an ultra-low noise
laser. The dependence of the storage time on laser noise is investigated.Comment: 4 pages 3 figures Revised 17.07.2001; Corrected calibration of noise
measm
Quantum description of light pulse scattering on a single atom in waveguides
We present a time dependent quantum calculation of the scattering of a
few-photon pulse on a single atom. The photon wave packet is assumed to
propagate in a transversely strongly confined geometry, which ensures strong
atom-light coupling and allows a quasi 1D treatment. The amplitude and phase of
the transmitted, reflected and transversely scattered part of the wave packet
strongly depend on the pulse length (bandwidth) and energy. For a transverse
mode size of the order of , we find nonlinear behavior for a few
photons already, or even for a single photon. In a second step we study the
collision of two such wave packets at the atomic site and find striking
differences between Fock state and coherent state wave packets of the same
photon number.Comment: to appear in Phys. Rev.
Two-atom dark states in electromagnetic cavities
The center-of-mass motion of two two-level atoms coupled to a single damped
mode of an electromagnetic resonator is investigated. For the case of one atom
being initially excited and the cavity mode in the vacuum state it is shown
that the atomic time evolution is dominated by the appearance of dark states.
These states, in which the initial excitation is stored in the internal atomic
degrees of freedom and the atoms become quantum mechanically entangled, are
almost immune against photon loss from the cavity. Various properties of the
dark states within and beyond the Raman-Nath approximation of atom optics are
worked out.Comment: 8 pages, 4 figure
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