1,028 research outputs found
On the consequences of the fact that atomic levels have a certain width
This note presents two ideas. The first one is that quantum theory has a
fundamentally perturbative basis but leads to nonperturbative states which it
would seem natural to take into account in the foundation of a theory of
quantum phenomena. The second one consists in questioning the validity of the
present notion of time. Both matters are related to the fact that atomic levels
have a certain width. This note is presented qualitatively so as to evidence
its main points, independently of the models on which these have been tested.Comment: 8 page
Frequency stability of maser oscillators operated with cavity Q
The short term frequency stability of masers equipped with an external feedback loop to increase the cavity quality factor was studied. The frequency stability of a hydrogen and a rubidium maser were measured and compared with theoretical evaluation. It is shown that the frequency stability passes through an optimum when the cavity Q is varied. Long term fluctuations are discussed and the optimum mid term frequency stability achievably by small size active and passive H-masers is considered
Influence of modulation frequency in rubidium cell frequency standards
The error signal which is used to control the frequency of the quartz crystal oscillator of a passive rubidium cell frequency standard is considered. The value of the slope of this signal, for an interrogation frequency close to the atomic transition frequency is calculated and measured for various phase (or frequency) modulation waveforms, and for several values of the modulation frequency. A theoretical analysis is made using a model which applies to a system in which the optical pumping rate, the relaxation rates and the RF field are homogeneous. Results are given for sine-wave phase modulation, square-wave frequency modulation and square-wave phase modulation. The influence of the modulation frequency on the slope of the error signal is specified. It is shown that the modulation frequency can be chosen as large as twice the non-saturated full-width at half-maximum without a drastic loss of the sensitivity to an offset of the interrogation frequency from center line, provided that the power saturation factor and the amplitude of modulation are properly adjusted
Prospects for atomic frequency standards
The potentialities of different atomic frequency standards which are not yet into field operation, for most of them, but for which preliminary data, obtained in laboratory experiments, give confidence that they may improve greatly the present state of the art are described. The review will mainly cover the following devices: (1) cesium beam frequency standards with optical pumping and detection; (2) optically pumped rubidium cells; (3) magnesium beam; (4) cold hydrogen masers; and (5) traps with stored and cooled ions
The Equivalence Principle as a Stepping Stone from Special to General Relativity: A Socratic Dialog
In this paper we show how the student can be led to an understanding of the
connection between special relativity and general relativity by considering the
time dilation effect of clocks placed on the surface of the Earth. This paper
is written as a Socratic dialog between a lecturer Sam and a student Kim.Comment: 8 pages, 1 figure, uses the revtex4 documentclass. Submitted to the
American Journal of Physics. Minor modification and corrections following
referees' comment
Robust two-dimensional subrecoil Raman cooling by adiabatic transfer in a tripod atomic system
We demonstrate two-dimensional robust Raman cooling in a four-level tripod
system, in which velocity-selective population transfer is achieved by a STIRAP
pulse. In contrast to basic 2D Raman cooling with square envelope pulses [Phys.
Rev. A 83, 023407 (2011)], the technique presented here allows for a wide
variation in the pulse duration and amplitude once the adiabaticity criterion
is satisfied. An efficient population transfer together with attaining of a
narrow spread of the resonant-velocity group leads to the narrowing of the
velocity-distribution spread down to , corresponding to an
effective temperature equal to . This robust method opens
new possibilities for cooling of neutral atoms.Comment: 8 pages, 3 figure
Creation and manipulation of Feshbach resonances with radio-frequency radiation
We present a simple technique for studying collisions of ultracold atoms in
the presence of a magnetic field and radio-frequency radiation (rf). Resonant
control of scattering properties can be achieved by using rf to couple a
colliding pair of atoms to a bound state. We show, using the example of 6Li,
that in some ranges of rf frequency and magnetic field this can be done without
giving rise to losses. We also show that halo molecules of large spatial extent
require much less rf power than deeply bound states. Another way to exert
resonant control is with a set of rf-coupled bound states, linked to the
colliding pair through the molecular interactions that give rise to
magnetically tunable Feshbach resonances. This was recently demonstrated for
87Rb [Kaufman et al., Phys. Rev. A 80:050701(R), 2009]. We examine the
underlying atomic and molecular physics which made this possible. Lastly, we
consider the control that may be exerted over atomic collisions by placing
atoms in superpositions of Zeeman states, and suggest that it could be useful
where small changes in scattering length are required. We suggest other species
for which rf and magnetic field control could together provide a useful tuning
mechanism.Comment: 21 pages, 8 figures, submitted to New Journal of Physic
Anthropologie historique du combat et de la violence de guerre au XXe siècle
Stéphane Audoin-Rouzeau, directeur d’études Guerre et paix : porosités Le séminaire s’était donné pour objectif, au cours de cette année, de commencer d’examiner les situations de contiguïté et de porosité entre l’activité guerrière et les activités sociales du temps de paix, activités banales, licites, voire encouragées dans le cadre des sociétés « à haut niveau de pacification » évoquées en son temps par Norbert Elias. Le sport, et en particulier le football, a retenu tout d’abord notre att..
Anthropologie historique du combat et de la violence de guerre au XXe siècle
Stéphane Audoin-Rouzeau, directeur d’études Moyens et difficultés d’une approche Au cours de l’année écoulée, le séminaire entendait se concentrer sur l’inventaire des moyens et des difficultés d’approche d’un sujet comme celui du combat et de la violence de guerre au sein de l’aire occidentale au XXe siècle. Après avoir posé la problématique générale du séminaire, dont le travail sur ce point précis est destiné à s’étendre sur deux années, puis après avoir tenté de faire l’inventaire des obs..
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